fs_backing_store.c

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/*
 * Copyright 2014 Vincent Sanders <vince@netsurf-browser.org>
 *
 * This file is part of NetSurf, http://www.netsurf-browser.org/
 *
 * NetSurf is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * NetSurf is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
/**
 * \file
 * Low-level resource cache persistent storage implementation.
 *
 * file based backing store.
 *
 * \todo Consider improving eviction sorting to include objects size
 *         and remaining lifetime and other cost metrics.
 *
 * \todo Implement mmap retrieval where supported.
 *
 * \todo Implement static retrieval for metadata objects as their heap
 *         lifetime is typically very short, though this may be obsoleted
 *         by a small object storage strategy.
 *
 */
 
#include <unistd.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <errno.h>
#include <time.h>
#include <stdlib.h>
#include <nsutils/unistd.h>
 
#include "netsurf/inttypes.h"
#include "utils/filepath.h"
#include "utils/file.h"
#include "utils/nsurl.h"
#include "utils/log.h"
#include "utils/messages.h"
#include "utils/hashmap.h"
#include "desktop/gui_internal.h"
#include "netsurf/misc.h"
 
#include "content/backing_store.h"
 
/** Backing store file format version */
#define CONTROL_VERSION 202
 
/**
 * Number of milliseconds after a update before control data
 * maintenance is performed
 */
#define CONTROL_MAINT_TIME 10000
 
/** Filename of serialised entries */
#define ENTRIES_FNAME "entries"
 
/** Filename of block file index */
#define BLOCKS_FNAME "blocks"
 
/** log2 block data address length (64k) */
#define BLOCK_ADDR_LEN 16
 
/** log2 number of entries per block file(1024) */
#define BLOCK_ENTRY_COUNT 10
 
/** log2 number of data block files */
#define BLOCK_FILE_COUNT (BLOCK_ADDR_LEN - BLOCK_ENTRY_COUNT)
 
/** log2 size of data blocks (8k) */
#define BLOCK_DATA_SIZE 13
 
/** log2 size of metadata blocks (8k) */
#define BLOCK_META_SIZE 13
 
/** length in bytes of a block files use map */
#define BLOCK_USE_MAP_SIZE (1 << (BLOCK_ENTRY_COUNT - 3))
 
/**
 * The type used as a binary identifier for each entry derived from
 * the URL. A larger identifier will have fewer collisions but
 * requires proportionately more storage.
 */
typedef uint32_t entry_ident_t;
 
/**
 * The type used to store block file index values. If this is changed
 * it will affect the entry storage/alignment and BLOCK_ADDR_LEN must
 * also be updated.
 */
typedef uint16_t block_index_t;
 
 
/**
 * Entry element index values.
 */
enum store_entry_elem_idx {
        ENTRY_ELEM_DATA = 0, /**< entry element is data */
        ENTRY_ELEM_META = 1,  /**< entry element is metadata */
        ENTRY_ELEM_COUNT = 2, /**< count of elements on an entry */
};
 
/**
 * flags that indicate what additional information is contained within
 * an entry element.
 */
enum store_entry_elem_flags {
        /** store not managing any allocation on entry */
        ENTRY_ELEM_FLAG_NONE = 0,
        /** entry data allocation is on heap */
        ENTRY_ELEM_FLAG_HEAP = 0x1,
        /** entry data allocation is mmaped */
        ENTRY_ELEM_FLAG_MMAP = 0x2,
        /** entry data allocation is in small object pool */
        ENTRY_ELEM_FLAG_SMALL = 0x4,
};
 
 
enum store_entry_flags {
        /** entry is normal */
        ENTRY_FLAGS_NONE = 0,
        /** entry has been invalidated but something still holding a reference */
        ENTRY_FLAGS_INVALID = 1,
};
 
/**
 * Backing store entry element.
 *
 * An element keeps data about:
 *  - the current memory allocation
 *  - the number of outstanding references to the memory
 *  - the size of the element data
 *  - flags controlling how the memory and element are handled
 *
 * @note Order is important to avoid excessive structure packing overhead.
 */
struct store_entry_element {
        uint8_t* data; /**< data allocated */
        uint32_t size; /**< size of entry element on disc */
        block_index_t block; /**< small object data block */
        uint8_t ref; /**< element data reference count */
        uint8_t flags; /**< entry flags */
};
 
/**
 * Backing store object index entry.
 *
 * An entry in the backing store contains two elements for the actual
 * data and the metadata. The two elements are treated identically for
 * storage lifetime but as a collective whole for expiration and
 * indexing.
 *
 * @note Order is important to avoid excessive structure packing overhead.
 */
struct store_entry {
        nsurl *url; /**< The URL for this entry */
        int64_t last_used; /**< UNIX time the entry was last used */
        uint16_t use_count; /**< number of times this entry has been accessed */
        uint8_t flags; /**< entry flags */
        /** Entry element (data or meta) specific information */
        struct store_entry_element elem[ENTRY_ELEM_COUNT];
};
 
/**
 * Small block file.
 */
struct block_file {
        /** file descriptor of the block file */
        int fd;
        /** map of used and unused entries within the block file */
        uint8_t use_map[BLOCK_USE_MAP_SIZE];
};
 
/**
 * log2 of block size.
 */
static const unsigned int log2_block_size[ENTRY_ELEM_COUNT] = {
        BLOCK_DATA_SIZE, /**< Data block size */
        BLOCK_META_SIZE  /**< Metadata block size */
};
 
/**
 * Parameters controlling the backing store.
 */
struct store_state {
        /* store config */
        char *path; /**< The path to the backing store */
        size_t limit; /**< The backing store upper bound target size */
        size_t hysteresis; /**< The hysteresis around the target size */
 
        /**
         * The cache object hash
         */
        hashmap_t *entries;
 
        /** flag indicating if the entries have been made persistent
         * since they were last changed.
         */
        bool entries_dirty;
 
        /** small block indexes */
        struct block_file blocks[ENTRY_ELEM_COUNT][BLOCK_FILE_COUNT];
 
        /** flag indicating if the block file use maps have been made
         * persistent since they were last changed.
         */
        bool blocks_dirty;
 
        /** flag indicating if a block file has been opened for update
         * since maintenance was previously done.
         */
        bool blocks_opened;
 
 
        /* stats */
        uint64_t total_alloc; /**< total size of all allocated storage. */
 
        size_t hit_count; /**< number of cache hits */
        uint64_t hit_size; /**< size of storage served */
        size_t miss_count; /**< number of cache misses */
 
};
 
/**
 * Global storage state.
 *
 * @todo Investigate if there is a way to have a context rather than
 * use a global.
 */
struct store_state *storestate;
 
/* Entries hashmap parameters
 *
 * Our hashmap has nsurl keys and store_entry values
 */
 
static bool
entries_hashmap_key_eq(void *key1, void *key2)
{
        return nsurl_compare((nsurl *)key1, (nsurl *)key2, NSURL_COMPLETE);
}
 
static void *
entries_hashmap_value_alloc(void *key)
{
        struct store_entry *ent = calloc(1, sizeof(struct store_entry));
        if (ent != NULL) {
                ent->url = nsurl_ref(key);
        }
        return ent;
}
 
static void
entries_hashmap_value_destroy(void *value)
{
        struct store_entry *ent = value;
        /** \todo Do we need to do any disk cleanup here?  if so, meep! */
        nsurl_unref(ent->url);
        free(ent);
}
 
static hashmap_parameters_t entries_hashmap_parameters = {
        .key_clone = (hashmap_key_clone_t)nsurl_ref,
        .key_destroy = (hashmap_key_destroy_t)nsurl_unref,
        .key_hash = (hashmap_key_hash_t)nsurl_hash,
        .key_eq = entries_hashmap_key_eq,
        .value_alloc = entries_hashmap_value_alloc,
        .value_destroy = entries_hashmap_value_destroy,
};
 
/**
 * Generate a filename for an object.
 *
 * this generates the filename for an object on disc. It is necessary
 * for this to generate a filename which conforms to the limitations
 * of all the filesystems the cache can be placed upon.
 *
 * From http://en.wikipedia.org/wiki/Comparison_of_file_systems#Limits
 * the relevant subset is:
 *  - path elements no longer than 8 characters
 *  - acceptable characters are A-Z, 0-9
 *  - short total path lengths (255 or less)
 *  - no more than 77 entries per directory (6bits worth)
 *
 * The short total path lengths mean the encoding must represent as
 * much data as possible in the least number of characters.
 *
 * To achieve all these goals we use RFC4648 base32 encoding which
 * packs 5bits into each character of the filename. To represent a 32
 * bit ident this requires a total path length of between 17 and 22
 * bytes (including directory separators) BA/BB/BC/BD/BE/ABCDEFG
 *
 * @note Version 1.00 of the cache implementation used base64 to
 * encode this, however that did not meet the requirement for only
 * using uppercase characters.
 *
 * @note Versions prior to 1.30 only packed 5 bits per directory level
 * A/B/C/D/E/F/ABCDEFG which only required 19 characters to represent
 * but resulted in requiring an extra level of directory which is less
 * desirable than the three extra characters using six bits.
 *
 * @param state The store state to use.
 * @param ident The identifier to use.
 * @param elem_idx The element index.
 * @return The filename string or NULL on allocation error.
 */
static char *
store_fname(struct store_state *state,
            entry_ident_t ident,
            int elem_idx)
{
        char *fname = NULL;
        uint8_t b32u_i[8]; /* base32 encoded ident */
        const uint8_t *b32u_d[6]; /* base32 ident as separate components */
 
        /* directories used to separate elements */
        const char *base_dir_table[] = {
                "d", "m", "dblk", "mblk"
        };
 
        /* RFC4648 base32 encoding table (six bits) */
        const uint8_t encoding_table[64][3] = {
                { 'A',   0, 0 }, { 'B',   0, 0 }, /*  0 */
                { 'C',   0, 0 }, { 'D',   0, 0 }, /*  2 */
                { 'E',   0, 0 }, { 'F',   0, 0 }, /*  4 */
                { 'G',   0, 0 }, { 'H',   0, 0 }, /*  6 */
                { 'I',   0, 0 }, { 'J',   0, 0 }, /*  8 */
                { 'K',   0, 0 }, { 'L',   0, 0 }, /* 10 */
                { 'M',   0, 0 }, { 'N',   0, 0 }, /* 12 */
                { 'O',   0, 0 }, { 'P',   0, 0 }, /* 14 */
                { 'Q',   0, 0 }, { 'R',   0, 0 }, /* 16 */
                { 'S',   0, 0 }, { 'T',   0, 0 }, /* 18 */
                { 'U',   0, 0 }, { 'V',   0, 0 }, /* 20 */
                { 'W',   0, 0 }, { 'X',   0, 0 }, /* 22 */
                { 'Y',   0, 0 }, { 'Z',   0, 0 }, /* 24 */
                { '2',   0, 0 }, { '3',   0, 0 }, /* 26 */
                { '4',   0, 0 }, { '5',   0, 0 }, /* 28 */
                { '6',   0, 0 }, { '7',   0, 0 }, /* 30 */
                { 'B', 'A', 0 }, { 'B', 'B', 0 }, /* 32 */
                { 'B', 'C', 0 }, { 'B', 'D', 0 }, /* 34 */
                { 'B', 'E', 0 }, { 'B', 'F', 0 }, /* 36 */
                { 'B', 'G', 0 }, { 'B', 'H', 0 }, /* 38 */
                { 'B', 'I', 0 }, { 'B', 'J', 0 }, /* 40 */
                { 'B', 'K', 0 }, { 'B', 'L', 0 }, /* 42 */
                { 'B', 'M', 0 }, { 'B', 'N', 0 }, /* 44 */
                { 'B', 'O', 0 }, { 'B', 'P', 0 }, /* 46 */
                { 'B', 'Q', 0 }, { 'B', 'R', 0 }, /* 48 */
                { 'B', 'S', 0 }, { 'B', 'T', 0 }, /* 50 */
                { 'B', 'U', 0 }, { 'B', 'V', 0 }, /* 52 */
                { 'B', 'W', 0 }, { 'B', 'X', 0 }, /* 54 */
                { 'B', 'Y', 0 }, { 'B', 'Z', 0 }, /* 56 */
                { 'B', '2', 0 }, { 'B', '3', 0 }, /* 58 */
                { 'B', '4', 0 }, { 'B', '5', 0 }, /* 60 */
                { 'B', '6', 0 }, { 'B', '7', 0 }  /* 62 */
        };
 
        /* base32 encode ident */
        b32u_i[0] = encoding_table[(ident      ) & 0x1f][0];
        b32u_i[1] = encoding_table[(ident >>  5) & 0x1f][0];
        b32u_i[2] = encoding_table[(ident >> 10) & 0x1f][0];
        b32u_i[3] = encoding_table[(ident >> 15) & 0x1f][0];
        b32u_i[4] = encoding_table[(ident >> 20) & 0x1f][0];
        b32u_i[5] = encoding_table[(ident >> 25) & 0x1f][0];
        b32u_i[6] = encoding_table[(ident >> 30) & 0x1f][0];
        b32u_i[7] = 0; /* null terminate ident string */
 
        /* base32 encode directory separators */
        b32u_d[0] = (uint8_t*)base_dir_table[elem_idx];
        b32u_d[1] = &encoding_table[(ident      ) & 0x3f][0];
        b32u_d[2] = &encoding_table[(ident >>  6) & 0x3f][0];
        b32u_d[3] = &encoding_table[(ident >> 12) & 0x3f][0];
        b32u_d[4] = &encoding_table[(ident >> 18) & 0x3f][0];
        b32u_d[5] = &encoding_table[(ident >> 24) & 0x3f][0];
 
        switch (elem_idx) {
        case ENTRY_ELEM_DATA:
        case ENTRY_ELEM_META:
                netsurf_mkpath(&fname, NULL, 8,
                               state->path, b32u_d[0], b32u_d[1], b32u_d[2],
                               b32u_d[3], b32u_d[4], b32u_d[5], b32u_i);
                break;
 
        case (ENTRY_ELEM_COUNT + ENTRY_ELEM_META):
        case (ENTRY_ELEM_COUNT + ENTRY_ELEM_DATA):
                netsurf_mkpath(&fname, NULL, 3,
                               state->path, b32u_d[0], b32u_d[1]);
                break;
 
        default:
                assert("bad element index" == NULL);
                break;
        }
 
        return fname;
}
 
/**
 * invalidate an element of an entry
 *
 * @param state The store state to use.
 * @param bse The entry to invalidate.
 * @param elem_idx The element index to invalidate.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
invalidate_element(struct store_state *state,
                   struct store_entry *bse,
                   int elem_idx)
{
        if (bse->elem[elem_idx].block != 0) {
                block_index_t bf;
                block_index_t bi;
 
                /* block file block resides in */
                bf = (bse->elem[elem_idx].block >> BLOCK_ENTRY_COUNT) &
                        ((1 << BLOCK_FILE_COUNT) - 1);
 
                /* block index in file */
                bi = bse->elem[elem_idx].block & ((1U << BLOCK_ENTRY_COUNT) -1);
 
                /* clear bit in use map */
                state->blocks[elem_idx][bf].use_map[bi >> 3] &= ~(1U << (bi & 7));
        } else {
                char *fname;
 
                /* unlink the file from disc */
                fname = store_fname(state, nsurl_hash(bse->url), elem_idx);
                if (fname == NULL) {
                        return NSERROR_NOMEM;
                }
                unlink(fname);
                free(fname);
        }
 
        state->total_alloc -= bse->elem[elem_idx].size;
 
        return NSERROR_OK;
}
 
/**
 * Remove the entry and files associated with an identifier.
 *
 * @param state The store state to use.
 * @param bse The entry to invalidate.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
invalidate_entry(struct store_state *state, struct store_entry *bse)
{
        nserror ret;
 
        /* mark entry as invalid */
        bse->flags |= ENTRY_FLAGS_INVALID;
 
        /* check if the entry has storage already allocated */
        if (((bse->elem[ENTRY_ELEM_DATA].flags &
             (ENTRY_ELEM_FLAG_HEAP | ENTRY_ELEM_FLAG_MMAP)) != 0) ||
            ((bse->elem[ENTRY_ELEM_META].flags &
              (ENTRY_ELEM_FLAG_HEAP | ENTRY_ELEM_FLAG_MMAP)) != 0)) {
                /*
                 * This entry cannot be immediately removed as it has
                 * associated allocation so wait for allocation release.
                 */
                NSLOG(netsurf, DEBUG,
                      "invalidating entry with referenced allocation");
                return NSERROR_OK;
        }
 
        NSLOG(netsurf, VERBOSE, "Removing entry for %s", nsurl_access(bse->url));
 
        ret = invalidate_element(state, bse, ENTRY_ELEM_META);
        if (ret != NSERROR_OK) {
                NSLOG(netsurf, ERROR, "Error invalidating metadata element");
        }
 
        ret = invalidate_element(state, bse, ENTRY_ELEM_DATA);
        if (ret != NSERROR_OK) {
                NSLOG(netsurf, ERROR, "Error invalidating data element");
        }
 
        /* As our final act we remove bse from the cache */
        hashmap_remove(state->entries, bse->url);
        /* From now, bse is invalid memory */
 
        return NSERROR_OK;
}
 
 
/**
 * Quick sort comparison.
 */
static int compar(const void *va, const void *vb)
{
        const struct store_entry *a = *(const struct store_entry **)va;
        const struct store_entry *b = *(const struct store_entry **)vb;
 
        /* consider the allocation flags - if an entry has an
         * allocation it is considered more valuable as it cannot be
         * freed.
         */
        if ((a->elem[ENTRY_ELEM_DATA].flags == ENTRY_ELEM_FLAG_NONE) &&
            (b->elem[ENTRY_ELEM_DATA].flags != ENTRY_ELEM_FLAG_NONE)) {
                return -1;
        } else if ((a->elem[ENTRY_ELEM_DATA].flags != ENTRY_ELEM_FLAG_NONE) &&
                   (b->elem[ENTRY_ELEM_DATA].flags == ENTRY_ELEM_FLAG_NONE)) {
                return 1;
        }
 
        if ((a->elem[ENTRY_ELEM_META].flags == ENTRY_ELEM_FLAG_NONE) &&
            (b->elem[ENTRY_ELEM_META].flags != ENTRY_ELEM_FLAG_NONE)) {
                return -1;
        } else if ((a->elem[ENTRY_ELEM_META].flags != ENTRY_ELEM_FLAG_NONE) &&
                   (b->elem[ENTRY_ELEM_META].flags == ENTRY_ELEM_FLAG_NONE)) {
                return 1;
        }
 
        if (a->use_count < b->use_count) {
                return -1;
        } else if (a->use_count > b->use_count) {
                return 1;
        }
        /* use count is the same - now consider last use time */
 
        if (a->last_used < b->last_used) {
                return -1;
        } else if (a->last_used > b->last_used) {
                return 1;
        }
 
        /* they are the same */
        return 0;
}
 
typedef struct {
        struct store_entry **elist;
        size_t ent_count;
} eviction_state_t;
 
/**
 * Iterator for gathering entries to compute eviction order
 */
static bool
entry_eviction_iterator_cb(void *key, void *value, void *ctx)
{
        eviction_state_t *estate = ctx;
        struct store_entry *ent = value;
        estate->elist[estate->ent_count++] = ent;
        return false;
}
 
/**
 * Evict entries from backing store as per configuration.
 *
 * Entries are evicted to ensure the cache remains within the
 * configured limits on size and number of entries.
 *
 * The approach is to check if the cache limits have been exceeded and
 * if so build and sort list of entries to evict. The list is sorted
 * by use count and then by age, so oldest object with least number of uses
 * get evicted first.
 *
 * @param state The store state to use.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror store_evict(struct store_state *state)
{
        size_t ent = 0;
        size_t removed = 0; /* size of removed entries */
        nserror ret = NSERROR_OK;
        size_t old_count;
        eviction_state_t estate;
 
        /* check if the cache has exceeded configured limit */
        if (state->total_alloc < state->limit) {
                /* cache within limits */
                return NSERROR_OK;
        }
 
        NSLOG(netsurf, INFO,
              "Evicting entries to reduce %"PRIu64" by %"PRIsizet,
              state->total_alloc,
              state->hysteresis);
 
        /* allocate storage for the list */
        old_count = hashmap_count(state->entries);
        estate.ent_count = 0;
        estate.elist = malloc(sizeof(struct state_entry*) * old_count);
        if (estate.elist == NULL) {
                return NSERROR_NOMEM;
        }
 
        if (hashmap_iterate(state->entries, entry_eviction_iterator_cb, &estate)) {
                NSLOG(netsurf, WARNING, "Unexpected termination of eviction iterator");
                free(estate.elist);
                return NSERROR_UNKNOWN;
        }
 
        if (old_count != estate.ent_count) {
                NSLOG(netsurf, WARNING, "Incorrect entry count after eviction iterator");
                free(estate.elist);
                return NSERROR_UNKNOWN;
        }
 
        qsort(estate.elist, estate.ent_count, sizeof(struct state_entry*), compar);
 
        /* evict entries in listed order */
        removed = 0;
        for (ent = 0; ent < estate.ent_count; ent++) {
                struct store_entry *bse = estate.elist[ent];
 
                removed += bse->elem[ENTRY_ELEM_DATA].size;
                removed += bse->elem[ENTRY_ELEM_META].size;
 
                ret = invalidate_entry(state, bse);
                if (ret != NSERROR_OK) {
                        break;
                }
 
                if (removed > state->hysteresis) {
                        break;
                }
        }
 
        free(estate.elist);
 
        NSLOG(netsurf, INFO,
              "removed %"PRIsizet" in %"PRIsizet" entries, %"PRIu64" remaining in %"PRIsizet" entries",
              removed, ent, state->total_alloc, old_count - ent);
 
        return ret;
}
 
/**
 * Write a single store entry to disk
 *
 * To serialise a single store entry for now we write out a 32bit int
 * which is the length of the url, then that many bytes of the url.
 * Then we write out the full store entry struct as-is, which includes
 * a useless nsurl pointer.
 */
static nserror
write_entry(struct store_entry *ent, int fd)
{
        uint32_t len = strlen(nsurl_access(ent->url));
        if (write(fd, &len, sizeof(len)) != sizeof(len))
                return NSERROR_SAVE_FAILED;
        if (write(fd, nsurl_access(ent->url), len) != (ssize_t)len)
                return NSERROR_SAVE_FAILED;
        if (write(fd, ent, sizeof(*ent)) != sizeof(*ent))
                return NSERROR_SAVE_FAILED;
 
        return NSERROR_OK;
}
 
typedef struct {
        int fd;
        size_t written;
} write_entry_iteration_state;
 
/**
 * Callback for iterating the entries hashmap
 */
static bool
write_entry_iterator(void *key, void *value, void *ctx)
{
        /* We ignore the key */
        struct store_entry *ent = value;
        write_entry_iteration_state *state = ctx;
        state->written++;
        /* We stop early if we fail to write this entry */
        return write_entry(ent, state->fd) != NSERROR_OK;
}
 
/**
 * Write filesystem entries to file.
 *
 * Serialise entry index out to storage.
 *
 * @param state The backing store state to serialise.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror write_entries(struct store_state *state)
{
        char *tname = NULL; /* temporary file name for atomic replace */
        char *fname = NULL; /* target filename */
        write_entry_iteration_state weistate;
        nserror ret;
 
        memset(&weistate, 0, sizeof(weistate));
 
        if (state->entries_dirty == false) {
                /* entries have not been updated since last write */
                return NSERROR_OK;
        }
 
        ret = netsurf_mkpath(&tname, NULL, 2, state->path, "t"ENTRIES_FNAME);
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        weistate.fd = open(tname, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
        if (weistate.fd == -1) {
                free(tname);
                return NSERROR_SAVE_FAILED;
        }
 
        if (hashmap_iterate(state->entries, write_entry_iterator, &weistate)) {
                /* The iteration ended early, so we failed */
                close(weistate.fd);
                unlink(tname);
                free(tname);
                return NSERROR_SAVE_FAILED;
        }
 
        close(weistate.fd);
 
        ret = netsurf_mkpath(&fname, NULL, 2, state->path, ENTRIES_FNAME);
        if (ret != NSERROR_OK) {
                unlink(tname);
                free(tname);
                return ret;
        }
 
        /* remove() call is to handle non-POSIX rename() implementations */
        (void)remove(fname);
        if (rename(tname, fname) != 0) {
                unlink(tname);
                free(tname);
                free(fname);
                return NSERROR_SAVE_FAILED;
        }
 
        NSLOG(netsurf, INFO, "Wrote out %"PRIsizet" entries", weistate.written);
 
        return NSERROR_OK;
}
 
/**
 * Write block file use map to file.
 *
 * Serialise block file use map out to storage.
 *
 * \param state The backing store state to serialise.
 * \return NSERROR_OK on success or error code on failure.
 */
static nserror write_blocks(struct store_state *state)
{
        int fd;
        char *tname = NULL; /* temporary file name for atomic replace */
        char *fname = NULL; /* target filename */
        size_t blocks_size;
        size_t written = 0;
        size_t wr;
        nserror ret;
        int bfidx; /* block file index */
        int elem_idx;
 
        if (state->blocks_dirty == false) {
                /* blocks use maps have not been updated since last write */
                return NSERROR_OK;
        }
 
        ret = netsurf_mkpath(&tname, NULL, 2, state->path, "t"BLOCKS_FNAME);
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        fd = open(tname, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
        if (fd == -1) {
                free(tname);
                return NSERROR_SAVE_FAILED;
        }
 
        blocks_size = (BLOCK_FILE_COUNT * ENTRY_ELEM_COUNT) * BLOCK_USE_MAP_SIZE;
 
        for (elem_idx = 0; elem_idx < ENTRY_ELEM_COUNT; elem_idx++) {
                for (bfidx = 0; bfidx < BLOCK_FILE_COUNT; bfidx++) {
                        wr = write(fd,
                                   &state->blocks[elem_idx][bfidx].use_map[0],
                                   BLOCK_USE_MAP_SIZE);
                        if (wr != BLOCK_USE_MAP_SIZE) {
                                NSLOG(netsurf, DEBUG,
                                      "writing block file %d use index on file number %d failed",
                                      elem_idx,
                                      bfidx);
                                goto wr_err;
                        }
                        written += wr;
                }
        }
wr_err:
        close(fd);
 
        /* check all data was written */
        if (written != blocks_size) {
                unlink(tname);
                free(tname);
                return NSERROR_SAVE_FAILED;
        }
 
        ret = netsurf_mkpath(&fname, NULL, 2, state->path, BLOCKS_FNAME);
        if (ret != NSERROR_OK) {
                unlink(tname);
                free(tname);
                return ret;
        }
 
        /* remove() call is to handle non-POSIX rename() implementations */
        (void)remove(fname);
        if (rename(tname, fname) != 0) {
                unlink(tname);
                free(tname);
                free(fname);
                return NSERROR_SAVE_FAILED;
        }
 
        return NSERROR_OK;
}
 
/**
 * Ensures block files are of the correct extent
 *
 * block files have their extent set to their maximum size to ensure
 * subsequent reads and writes do not need to extend the file and are
 * therefore faster.
 *
 * \param state The backing store state to set block extent for.
 * \return NSERROR_OK on success or error code on failure.
 */
static nserror set_block_extents(struct store_state *state)
{
        int bfidx; /* block file index */
        int elem_idx;
        int ftr;
 
        if (state->blocks_opened == false) {
                /* no blocks have been opened since last write */
                return NSERROR_OK;
        }
 
        NSLOG(netsurf, DEBUG, "Starting");
        for (elem_idx = 0; elem_idx < ENTRY_ELEM_COUNT; elem_idx++) {
                for (bfidx = 0; bfidx < BLOCK_FILE_COUNT; bfidx++) {
                        if (state->blocks[elem_idx][bfidx].fd != -1) {
                                /* ensure block file is correct extent */
                                ftr = ftruncate(state->blocks[elem_idx][bfidx].fd, 1U << (log2_block_size[elem_idx] + BLOCK_ENTRY_COUNT));
                                if (ftr == -1) {
                                        NSLOG(netsurf, ERROR,
                                              "Truncate failed errno:%d",
                                              errno);
                                }
                        }
                }
        }
        NSLOG(netsurf, DEBUG, "Complete");
 
        state->blocks_opened = false;
 
        return NSERROR_OK;
}
 
/**
 * maintenance of control structures.
 *
 * callback scheduled when control data has been update. Currently
 * this is for when the entries table is dirty and requires
 * serialising.
 *
 * \param s store state to maintain.
 */
static void control_maintenance(void *s)
{
        struct store_state *state = s;
 
        write_entries(state);
        write_blocks(state);
        set_block_extents(state);
}
 
 
/**
 * Lookup a backing store entry in the entry table from a url.
 *
 * This finds the store entry associated with the given
 * key. Additionally if an entry is found it updates the usage data
 * about the entry.
 *
 * @param state The store state to use.
 * @param url The value used as the unique key to search entries for.
 * @param bse Pointer used to return value.
 * @return NSERROR_OK and bse updated on success or NSERROR_NOT_FOUND
 *         if no entry corresponds to the url.
 */
static nserror
get_store_entry(struct store_state *state, nsurl *url, struct store_entry **bse)
{
        struct store_entry *ent;
 
        ent = hashmap_lookup(state->entries, url);
 
        if (ent == NULL) {
                return NSERROR_NOT_FOUND;
        }
 
        *bse = ent;
 
        ent->last_used = time(NULL);
        ent->use_count++;
 
        state->entries_dirty = true;
 
        guit->misc->schedule(CONTROL_MAINT_TIME, control_maintenance, state);
 
        return NSERROR_OK;
}
 
/**
 * Find next available small block.
 */
static block_index_t alloc_block(struct store_state *state, int elem_idx)
{
        int bf;
        int idx;
        int bit;
        uint8_t *map;
 
        for (bf = 0; bf < BLOCK_FILE_COUNT; bf++) {
                map = &state->blocks[elem_idx][bf].use_map[0];
 
                for (idx = 0; idx < BLOCK_USE_MAP_SIZE; idx++) {
                        if (*(map + idx) != 0xff) {
                                /* located an unused block */
                                for (bit = 0; bit < 8;bit++) {
                                        if (((*(map + idx)) & (1U << bit)) == 0) {
                                                /* mark block as used */
                                                *(map + idx) |= 1U << bit;
                                                state->blocks_dirty = true;
                                                return (((bf * BLOCK_USE_MAP_SIZE) + idx) * 8) + bit;
                                        }
                                }
                        }
                }
        }
 
        return 0;
}
 
/**
 * Set a backing store entry in the entry table from a url.
 *
 * This creates a backing store entry in the entry table for a url.
 *
 * @param state The store state to use.
 * @param url The value used as the unique key to search entries for.
 * @param elem_idx The index of the entry element to use.
 * @param data The data to store
 * @param datalen The length of data in \a data
 * @param bse Pointer used to return value.
 * @return NSERROR_OK and \a bse updated on success or NSERROR_NOT_FOUND
 *         if no entry corresponds to the url.
 */
static nserror
set_store_entry(struct store_state *state,
                nsurl *url,
                int elem_idx,
                uint8_t *data,
                const size_t datalen,
                struct store_entry **bse)
{
        struct store_entry *se;
        nserror ret;
        struct store_entry_element *elem;
 
        NSLOG(netsurf, DEBUG, "url:%s", nsurl_access(url));
 
        /* evict entries as required and ensure there is at least one
         * new entry available.
         */
        ret = store_evict(state);
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        se = hashmap_lookup(state->entries, url);
        if (se == NULL) {
                se = hashmap_insert(state->entries, url);
        }
        if (se == NULL) {
                return NSERROR_NOMEM;
        }
 
        /* the entry element */
        elem = &se->elem[elem_idx];
 
        /* check if the element has storage already allocated */
        if ((elem->flags & (ENTRY_ELEM_FLAG_HEAP | ENTRY_ELEM_FLAG_MMAP)) != 0) {
                /* this entry cannot be removed as it has associated
                 * allocation.
                 */
                NSLOG(netsurf, ERROR,
                      "attempt to overwrite entry with in use data");
                return NSERROR_PERMISSION;
        }
 
        /* set the common entry data */
        se->use_count = 1;
        se->last_used = time(NULL);
 
        /* store the data in the element */
        elem->flags |= ENTRY_ELEM_FLAG_HEAP;
        elem->data = data;
        elem->ref = 1;
 
        /* account for size of entry element */
        state->total_alloc -= elem->size;
        elem->size = datalen;
        state->total_alloc += elem->size;
 
        /* if the element will fit in a small block attempt to allocate one */
        if (elem->size <= (1U << log2_block_size[elem_idx])) {
                elem->block = alloc_block(state, elem_idx);
        }
 
        /* ensure control maintenance scheduled. */
        state->entries_dirty = true;
        guit->misc->schedule(CONTROL_MAINT_TIME, control_maintenance, state);
 
        *bse = se;
 
        return NSERROR_OK;
}
 
 
/**
 * Open a file using a store ident.
 *
 * @param state The store state to use.
 * @param ident The identifier to open file for.
 * @param elem_idx The element within the store entry to open. The
 *                 value should be be one of the values in the
 *                 store_entry_elem_idx enum. Additionally it may have
 *                 ENTRY_ELEM_COUNT added to it to indicate block file
 *                 names.
 * @param openflags The flags used with the open call.
 * @return An fd from the open call or -1 on error.
 */
static int
store_open(struct store_state *state,
           entry_ident_t ident,
           int elem_idx,
           int openflags)
{
        char *fname;
        nserror ret;
        int fd;
 
        fname = store_fname(state, ident, elem_idx);
        if (fname == NULL) {
                NSLOG(netsurf, ERROR, "filename error");
                return -1;
        }
 
        /* ensure all path elements to file exist if creating file */
        if (openflags & O_CREAT) {
                ret = netsurf_mkdir_all(fname);
                if (ret != NSERROR_OK) {
                        NSLOG(netsurf, WARNING,
                              "file path \"%s\" could not be created", fname);
                        free(fname);
                        return -1;
                }
        }
 
        NSLOG(netsurf, DEBUG, "opening %s", fname);
        fd = open(fname, openflags, S_IRUSR | S_IWUSR);
 
        free(fname);
 
        return fd;
}
 
 
/**
 * Unlink entries file
 *
 * @param state The backing store state.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
unlink_entries(struct store_state *state)
{
        char *fname = NULL;
        nserror ret;
 
        ret = netsurf_mkpath(&fname, NULL, 2, state->path, ENTRIES_FNAME);
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        unlink(fname);
 
        free(fname);
        return NSERROR_OK;
}
 
/**
 * Read description entries into memory.
 *
 * @param state The backing store state to put the loaded entries in.
 * @return NSERROR_OK on success or error code on faliure.
 */
static nserror
read_entries(struct store_state *state)
{
        char *fname = NULL;
        char *url;
        nsurl *nsurl;
        nserror ret;
        size_t read_entries = 0;
        struct store_entry *ent;
        int fd;
 
        ret = netsurf_mkpath(&fname, NULL, 2, state->path, ENTRIES_FNAME);
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        state->entries = hashmap_create(&entries_hashmap_parameters);
        if (state->entries == NULL) {
                free(fname);
                return NSERROR_NOMEM;
        }
 
        fd = open(fname, O_RDWR);
        if (fd != -1) {
                uint32_t urllen;
                while (read(fd, &urllen, sizeof(urllen)) == sizeof(urllen)) {
                        url = calloc(1, urllen+1);
                        if (url == NULL) {
                                close(fd);
                                free(fname);
                                return NSERROR_NOMEM;
                        }
                        if (read(fd, url, urllen) != (ssize_t)urllen) {
                                free(url);
                                close(fd);
                                free(fname);
                                return NSERROR_INIT_FAILED;
                        }
                        ret = nsurl_create(url, &nsurl);
                        if (ret != NSERROR_OK) {
                                free(url);
                                close(fd);
                                free(fname);
                                return ret;
                        }
                        free(url);
                        /* We have to be careful here about nsurl refs */
                        ent = hashmap_insert(state->entries, nsurl);
                        if (ent == NULL) {
                                nsurl_unref(nsurl);
                                close(fd);
                                free(fname);
                                return NSERROR_NOMEM;
                        }
                        /* At this point, ent actually owns a ref of nsurl */
                        if (read(fd, ent, sizeof(*ent)) != sizeof(*ent)) {
                                /* The read failed, so reset the ptr */
                                ent->url = nsurl; /* It already had a ref */
                                nsurl_unref(nsurl);
                                close(fd);
                                free(fname);
                                return NSERROR_INIT_FAILED;
                        }
                        ent->url = nsurl; /* It already owns a ref */
                        nsurl_unref(nsurl);
                        NSLOG(netsurf, DEBUG, "Successfully read entry for %s", nsurl_access(ent->url));
                        read_entries++;
                        /* Note the size allocation */
                        state->total_alloc += ent->elem[ENTRY_ELEM_DATA].size;
                        state->total_alloc += ent->elem[ENTRY_ELEM_META].size;
                        /* And ensure we don't pretend to have this in memory yet */
                        ent->elem[ENTRY_ELEM_DATA].flags &= ~(ENTRY_ELEM_FLAG_HEAP | ENTRY_ELEM_FLAG_MMAP);
                        ent->elem[ENTRY_ELEM_META].flags &= ~(ENTRY_ELEM_FLAG_HEAP | ENTRY_ELEM_FLAG_MMAP);
 
                }
                close(fd);
        }
 
        NSLOG(netsurf, INFO, "Read %"PRIsizet" entries from cache", read_entries);
 
        free(fname);
        return NSERROR_OK;
}
 
 
/**
 * Read block file usage bitmaps.
 *
 * @param state The backing store state to put the loaded entries in.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
read_blocks(struct store_state *state)
{
        int bfidx; /* block file index */
        int elem_idx;
        int fd;
        ssize_t rd;
        char *fname = NULL;
        nserror ret;
 
        ret = netsurf_mkpath(&fname, NULL, 2, state->path, BLOCKS_FNAME);
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        NSLOG(netsurf, INFO, "Initialising block use map from %s", fname);
 
        fd = open(fname, O_RDWR);
        free(fname);
        if (fd != -1) {
                /* initialise block file use array */
                for (elem_idx = 0; elem_idx < ENTRY_ELEM_COUNT; elem_idx++) {
                        for (bfidx = 0; bfidx < BLOCK_FILE_COUNT; bfidx++) {
                                rd = read(fd,
                                          &state->blocks[elem_idx][bfidx].use_map[0],
                                          BLOCK_USE_MAP_SIZE);
                                if (rd <= 0) {
                                        NSLOG(netsurf, ERROR,
                                              "reading block file %d use index on file number %d failed",
                                              elem_idx,
                                              bfidx);
                                        goto rd_err;
                                }
                        }
                }
        rd_err:
                close(fd);
 
        } else {
                NSLOG(netsurf, INFO, "Initialising block use map to defaults");
                /* ensure block 0 (invalid sentinel) is skipped */
                state->blocks[ENTRY_ELEM_DATA][0].use_map[0] = 1;
                state->blocks[ENTRY_ELEM_META][0].use_map[0] = 1;
        }
 
        /* initialise block file file descriptors */
        for (bfidx = 0; bfidx < BLOCK_FILE_COUNT; bfidx++) {
                state->blocks[ENTRY_ELEM_DATA][bfidx].fd = -1;
                state->blocks[ENTRY_ELEM_META][bfidx].fd = -1;
        }
 
        return NSERROR_OK;
}
 
/**
 * Write the cache tag file.
 *
 * @param state The cache state.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
write_cache_tag(struct store_state *state)
{
        FILE *fcachetag;
        nserror ret;
        char *fname = NULL;
 
        ret = netsurf_mkpath(&fname, NULL, 2, state->path, "CACHEDIR.TAG");
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        fcachetag = fopen(fname, "wb");
 
        free(fname);
 
        if (fcachetag == NULL) {
                return NSERROR_NOT_FOUND;
        }
 
        fprintf(fcachetag,
                "Signature: 8a477f597d28d172789f06886806bc55\n"
                "# This file is a cache directory tag created by NetSurf.\n"
                "# For information about cache directory tags, see:\n"
                "#      http://www.brynosaurus.com/cachedir/\n");
 
        fclose(fcachetag);
 
        return NSERROR_OK;
}
 
/**
 * Write the control file for the current state.
 *
 * @param state The state to write to the control file.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
write_control(struct store_state *state)
{
        FILE *fcontrol;
        nserror ret;
        char *fname = NULL;
 
        ret = netsurf_mkpath(&fname, NULL, 2, state->path, "control");
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        NSLOG(netsurf, INFO, "writing control file \"%s\"", fname);
 
        ret = netsurf_mkdir_all(fname);
        if (ret != NSERROR_OK) {
                free(fname);
                return ret;
        }
 
        fcontrol = fopen(fname, "wb");
 
        free(fname);
 
        if (fcontrol == NULL) {
                return NSERROR_NOT_FOUND;
        }
 
        fprintf(fcontrol, "%u%c", CONTROL_VERSION, 0);
 
        fclose(fcontrol);
 
        return NSERROR_OK;
}
 
 
/**
 * Read and parse the control file.
 *
 * @param state The state to read from the control file.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
read_control(struct store_state *state)
{
        nserror ret;
        FILE *fcontrol;
        unsigned int ctrlversion;
        char *fname = NULL;
 
        ret = netsurf_mkpath(&fname, NULL, 2, state->path, "control");
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        NSLOG(netsurf, INFO, "opening control file \"%s\"", fname);
 
        fcontrol = fopen(fname, "rb");
 
        free(fname);
 
        if (fcontrol == NULL) {
                /* unable to open control file */
                if (errno == ENOENT) {
                        return NSERROR_NOT_FOUND;
                } else {
                        return NSERROR_INIT_FAILED;
                }
        }
 
        /* read control and setup new state */
 
        /* first line is version */
        if (fscanf(fcontrol, "%u", &ctrlversion) != 1) {
                goto control_error;
        }
 
        if (ctrlversion != CONTROL_VERSION) {
                goto control_error;
        }
 
        if (fgetc(fcontrol) != 0) {
                goto control_error;
        }
 
        fclose(fcontrol);
 
        return NSERROR_OK;
 
control_error: /* problem with the control file */
 
        fclose(fcontrol);
 
        return NSERROR_INIT_FAILED;
}
 
 
 
 
/* Functions exported in the backing store table */
 
/**
 * Initialise the backing store.
 *
 * @param parameters to configure backing store.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
initialise(const struct llcache_store_parameters *parameters)
{
        struct store_state *newstate;
        nserror ret;
 
        /* check backing store is not already initialised */
        if (storestate != NULL) {
                return NSERROR_INIT_FAILED;
        }
 
        /* if we are not allowed any space simply give up on init */
        if (parameters->limit == 0) {
                return NSERROR_OK;
        }
 
        /* if the path to the cache directory is not set do not init */
        if (parameters->path == NULL) {
                return NSERROR_OK;
        }
 
        /* allocate new store state and set defaults */
        newstate = calloc(1, sizeof(struct store_state));
        if (newstate == NULL) {
                return NSERROR_NOMEM;
        }
 
        newstate->path = strdup(parameters->path);
        newstate->limit = parameters->limit;
        newstate->hysteresis = parameters->hysteresis;
 
        /* read store control and create new if required */
        ret = read_control(newstate);
        if (ret != NSERROR_OK) {
                if (ret == NSERROR_NOT_FOUND) {
                        NSLOG(netsurf, INFO, "cache control file not found, making fresh");
                } else {
                        NSLOG(netsurf, ERROR, "read control failed %s",
                              messages_get_errorcode(ret));
                        ret = netsurf_recursive_rm(newstate->path);
                        if (ret != NSERROR_OK) {
                                NSLOG(netsurf, WARNING, "Error `%s` while removing `%s`",
                                      messages_get_errorcode(ret), newstate->path);
                                NSLOG(netsurf, WARNING, "Unable to clean up partial cache state.");
                                NSLOG(netsurf, WARNING, "Funky behaviour may ensue.");
                        } else {
                                NSLOG(netsurf, INFO, "Successfully removed old cache from `%s`",
                                      newstate->path);
                        }
                }
                ret = write_control(newstate);
                if (ret == NSERROR_OK) {
                        unlink_entries(newstate);
                        write_cache_tag(newstate);
                }
        }
        if (ret != NSERROR_OK) {
                /* that went well obviously */
                free(newstate->path);
                free(newstate);
                return ret;
        }
 
        /* read filesystem entries */
        ret = read_entries(newstate);
        if (ret != NSERROR_OK) {
                /* that went well obviously */
                free(newstate->path);
                free(newstate);
                return ret;
        }
 
        /* read blocks */
        ret = read_blocks(newstate);
        if (ret != NSERROR_OK) {
                /* oh dear */
                hashmap_destroy(newstate->entries);
                free(newstate->path);
                free(newstate);
                return ret;
        }
 
        storestate = newstate;
 
        NSLOG(netsurf, INFO, "FS backing store init successful");
 
        NSLOG(netsurf, INFO,
              "path:%s limit:%"PRIsizet" hyst:%"PRIsizet,
              newstate->path,
              newstate->limit,
              newstate->hysteresis);
        NSLOG(netsurf, INFO, "Using %"PRIu64"/%"PRIsizet,
              newstate->total_alloc, newstate->limit);
 
        return NSERROR_OK;
}
 
 
/**
 * Finalise the backing store.
 *
 * \todo This will cause the backing store to leak any outstanding memory
 * allocations. This will probably best be done by a global use count.
 *
 * @return NSERROR_OK on success.
 */
static nserror
finalise(void)
{
        int bf; /* block file index */
        unsigned int op_count;
 
        if (storestate != NULL) {
                guit->misc->schedule(-1, control_maintenance, storestate);
                write_entries(storestate);
                write_blocks(storestate);
 
                /* ensure all block files are closed */
                for (bf = 0; bf < BLOCK_FILE_COUNT; bf++) {
                        if (storestate->blocks[ENTRY_ELEM_DATA][bf].fd != -1) {
                                close(storestate->blocks[ENTRY_ELEM_DATA][bf].fd);
                        }
                        if (storestate->blocks[ENTRY_ELEM_META][bf].fd != -1) {
                                close(storestate->blocks[ENTRY_ELEM_META][bf].fd);
                        }
                }
 
                op_count = storestate->hit_count + storestate->miss_count;
 
                /* avoid division by zero */
                if (op_count > 0) {
                        NSLOG(netsurf, INFO,
                              "Cache total/hit/miss/fail (counts) %d/%"PRIsizet"/%"PRIsizet"/%d (100%%/%"PRIsizet"%%/%"PRIsizet"%%/%d%%)",
                              op_count,
                              storestate->hit_count,
                              storestate->miss_count,
                              0,
                              (storestate->hit_count * 100) / op_count,
                              (storestate->miss_count * 100) / op_count,
                              0);
                }
 
                hashmap_destroy(storestate->entries);
                free(storestate->path);
                free(storestate);
                storestate = NULL;
        }
        return NSERROR_OK;
}
 
 
/**
 * Write an element of an entry to backing storage in a small block file.
 *
 * \param state The backing store state to use.
 * \param bse The entry to store
 * \param elem_idx The element index within the entry.
 * \return NSERROR_OK on success or error code.
 */
static nserror store_write_block(struct store_state *state,
                         struct store_entry *bse,
                         int elem_idx)
{
        block_index_t bf = (bse->elem[elem_idx].block >> BLOCK_ENTRY_COUNT) &
                ((1 << BLOCK_FILE_COUNT) - 1); /* block file block resides in */
        block_index_t bi = bse->elem[elem_idx].block & ((1U << BLOCK_ENTRY_COUNT) -1); /* block index in file */
        ssize_t wr;
        off_t offst;
 
        /* ensure the block file fd is good */
        if (state->blocks[elem_idx][bf].fd == -1) {
                state->blocks[elem_idx][bf].fd = store_open(state, bf,
                                elem_idx + ENTRY_ELEM_COUNT, O_CREAT | O_RDWR);
                if (state->blocks[elem_idx][bf].fd == -1) {
                        NSLOG(netsurf, ERROR, "Open failed errno %d", errno);
                        return NSERROR_SAVE_FAILED;
                }
 
                /* flag that a block file has been opened */
                state->blocks_opened = true;
        }
 
        offst = (unsigned int)bi << log2_block_size[elem_idx];
 
        wr = nsu_pwrite(state->blocks[elem_idx][bf].fd,
                        bse->elem[elem_idx].data,
                        bse->elem[elem_idx].size,
                        offst);
        if (wr != (ssize_t)bse->elem[elem_idx].size) {
                NSLOG(netsurf, ERROR,
                      "Write failed %"PRIssizet" of %"PRId32" bytes from %p at %"PRIsizet" block %"PRIu16" errno %d",
                      wr,
                      bse->elem[elem_idx].size,
                      bse->elem[elem_idx].data,
                      (size_t)offst,
                      bse->elem[elem_idx].block,
                      errno);
                return NSERROR_SAVE_FAILED;
        }
 
        NSLOG(netsurf, INFO,
              "Wrote %"PRIssizet" bytes from %p at %"PRIsizet" block %d", wr,
              bse->elem[elem_idx].data, (size_t)offst,
              bse->elem[elem_idx].block);
 
        return NSERROR_OK;
}
 
/**
 * Write an element of an entry to backing storage as an individual file.
 *
 * \param state The backing store state to use.
 * \param bse The entry to store
 * \param elem_idx The element index within the entry.
 * \return NSERROR_OK on success or error code.
 */
static nserror store_write_file(struct store_state *state,
                         struct store_entry *bse,
                         int elem_idx)
{
        ssize_t wr;
        int fd;
        int err;
 
        fd = store_open(state, nsurl_hash(bse->url), elem_idx, O_CREAT | O_WRONLY);
        if (fd < 0) {
                perror("");
                NSLOG(netsurf, ERROR, "Open failed %d errno %d", fd, errno);
                return NSERROR_SAVE_FAILED;
        }
 
        wr = write(fd, bse->elem[elem_idx].data, bse->elem[elem_idx].size);
        err = errno; /* close can change errno */
 
        close(fd);
        if (wr != (ssize_t)bse->elem[elem_idx].size) {
                NSLOG(netsurf, ERROR,
                      "Write failed %"PRIssizet" of %"PRId32" bytes from %p errno %d",
                      wr,
                      bse->elem[elem_idx].size,
                      bse->elem[elem_idx].data,
                      err);
 
                /** @todo Delete the file? */
                return NSERROR_SAVE_FAILED;
        }
 
        NSLOG(netsurf, VERBOSE, "Wrote %"PRIssizet" bytes from %p", wr,
              bse->elem[elem_idx].data);
 
        return NSERROR_OK;
}
 
/**
 * Place an object in the backing store.
 *
 * takes ownership of the heap block passed in.
 *
 * @param url The url is used as the unique primary key for the data.
 * @param bsflags The flags to control how the object is stored.
 * @param data The objects source data.
 * @param datalen The length of the \a data.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
store(nsurl *url,
      enum backing_store_flags bsflags,
      uint8_t *data,
      const size_t datalen)
{
        nserror ret;
        struct store_entry *bse;
        int elem_idx;
 
        /* check backing store is initialised */
        if (storestate == NULL) {
                return NSERROR_INIT_FAILED;
        }
 
        /* calculate the entry element index */
        if ((bsflags & BACKING_STORE_META) != 0) {
                elem_idx = ENTRY_ELEM_META;
        } else {
                elem_idx = ENTRY_ELEM_DATA;
        }
 
        /* set the store entry up */
        ret = set_store_entry(storestate, url, elem_idx, data, datalen, &bse);
        if (ret != NSERROR_OK) {
                NSLOG(netsurf, ERROR, "store entry setting failed");
                return ret;
        }
 
        if (bse->elem[elem_idx].block != 0) {
                /* small block storage */
                ret = store_write_block(storestate, bse, elem_idx);
        } else {
                /* separate file in backing store */
                ret = store_write_file(storestate, bse, elem_idx);
        }
 
        return ret;
}
 
/**
 * release any allocation for an entry
 */
static nserror entry_release_alloc(struct store_entry_element *elem)
{
        if ((elem->flags & ENTRY_ELEM_FLAG_HEAP) != 0) {
                elem->ref--;
                if (elem->ref == 0) {
                        NSLOG(netsurf, DEEPDEBUG, "freeing %p", elem->data);
                        free(elem->data);
                        elem->flags &= ~ENTRY_ELEM_FLAG_HEAP;
                }
        }
        return NSERROR_OK;
}
 
 
/**
 * Read an element of an entry from a small block file in the backing storage.
 *
 * \param state The backing store state to use.
 * \param bse The entry to read.
 * \param elem_idx The element index within the entry.
 * \return NSERROR_OK on success or error code.
 */
static nserror store_read_block(struct store_state *state,
                         struct store_entry *bse,
                         int elem_idx)
{
        block_index_t bf = (bse->elem[elem_idx].block >> BLOCK_ENTRY_COUNT) &
                ((1 << BLOCK_FILE_COUNT) - 1); /* block file block resides in */
        block_index_t bi = bse->elem[elem_idx].block & ((1 << BLOCK_ENTRY_COUNT) -1); /* block index in file */
        ssize_t rd;
        off_t offst;
 
        /* ensure the block file fd is good */
        if (state->blocks[elem_idx][bf].fd == -1) {
                state->blocks[elem_idx][bf].fd = store_open(state, bf,
                                elem_idx + ENTRY_ELEM_COUNT, O_CREAT | O_RDWR);
                if (state->blocks[elem_idx][bf].fd == -1) {
                        NSLOG(netsurf, ERROR, "Open failed errno %d", errno);
                        return NSERROR_SAVE_FAILED;
                }
 
                /* flag that a block file has been opened */
                state->blocks_opened = true;
        }
 
        offst = (unsigned int)bi << log2_block_size[elem_idx];
 
        rd = nsu_pread(state->blocks[elem_idx][bf].fd,
                       bse->elem[elem_idx].data,
                       bse->elem[elem_idx].size,
                       offst);
        if (rd != (ssize_t)bse->elem[elem_idx].size) {
                NSLOG(netsurf, ERROR,
                      "Failed reading %"PRIssizet" of %"PRId32" bytes into %p from %"PRIsizet" block %"PRIu16" errno %d",
                      rd,
                      bse->elem[elem_idx].size,
                      bse->elem[elem_idx].data,
                      (size_t)offst,
                      bse->elem[elem_idx].block,
                      errno);
                return NSERROR_SAVE_FAILED;
        }
 
        NSLOG(netsurf, DEEPDEBUG,
              "Read %"PRIssizet" bytes into %p from %"PRIsizet" block %d", rd,
              bse->elem[elem_idx].data, (size_t)offst,
              bse->elem[elem_idx].block);
 
        return NSERROR_OK;
}
 
/**
 * Read an element of an entry from an individual file in the backing storage.
 *
 * \param state The backing store state to use.
 * \param bse The entry to read.
 * \param elem_idx The element index within the entry.
 * \return NSERROR_OK on success or error code.
 */
static nserror store_read_file(struct store_state *state,
                         struct store_entry *bse,
                         int elem_idx)
{
        int fd;
        ssize_t rd; /* return from read */
        int ret = NSERROR_OK;
        size_t tot = 0; /* total size */
 
        /* separate file in backing store */
        fd = store_open(storestate, nsurl_hash(bse->url), elem_idx, O_RDONLY);
        if (fd < 0) {
                NSLOG(netsurf, ERROR, "Open failed %d errno %d", fd, errno);
                /** @todo should this invalidate the entry? */
                return NSERROR_NOT_FOUND;
        }
 
        while (tot < bse->elem[elem_idx].size) {
                rd = read(fd,
                          bse->elem[elem_idx].data + tot,
                          bse->elem[elem_idx].size - tot);
                if (rd <= 0) {
                        NSLOG(netsurf, ERROR,
                              "read error returned %"PRIssizet" errno %d",
                              rd,
                              errno);
                        ret = NSERROR_NOT_FOUND;
                        break;
                }
                tot += rd;
        }
 
        close(fd);
 
        NSLOG(netsurf, DEEPDEBUG, "Read %"PRIsizet" bytes into %p", tot,
              bse->elem[elem_idx].data);
 
        return ret;
}
 
/**
 * Retrieve an object from the backing store.
 *
 * @param[in] url The url is used as the unique primary key for the data.
 * @param[in] bsflags The flags to control how the object is retrieved.
 * @param[out] data_out The objects data.
 * @param[out] datalen_out The length of the \a data retrieved.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
fetch(nsurl *url,
      enum backing_store_flags bsflags,
      uint8_t **data_out,
      size_t *datalen_out)
{
        nserror ret;
        struct store_entry *bse;
        struct store_entry_element *elem;
        int elem_idx;
 
        /* check backing store is initialised */
        if (storestate == NULL) {
                return NSERROR_INIT_FAILED;
        }
 
        /* fetch store entry */
        ret = get_store_entry(storestate, url, &bse);
        if (ret != NSERROR_OK) {
                NSLOG(netsurf, DEBUG, "Entry for %s not found", nsurl_access(url));
                storestate->miss_count++;
                return ret;
        }
        storestate->hit_count++;
 
        NSLOG(netsurf, DEBUG, "retrieving cache data for url:%s",
              nsurl_access(url));
 
        /* calculate the entry element index */
        if ((bsflags & BACKING_STORE_META) != 0) {
                elem_idx = ENTRY_ELEM_META;
        } else {
                elem_idx = ENTRY_ELEM_DATA;
        }
        elem = &bse->elem[elem_idx];
 
        /* if an allocation already exists return it */
        if ((elem->flags & ENTRY_ELEM_FLAG_HEAP) != 0) {
                /* use the existing allocation and bump the ref count. */
                elem->ref++;
 
                NSLOG(netsurf, DEEPDEBUG,
                      "Using existing entry (%p) allocation %p refs:%d", bse,
                      elem->data, elem->ref);
 
        } else {
                /* allocate from the heap */
                elem->data = malloc(elem->size);
                if (elem->data == NULL) {
                        NSLOG(netsurf, ERROR,
                              "Failed to create new heap allocation");
                        return NSERROR_NOMEM;
                }
                NSLOG(netsurf, DEEPDEBUG, "Created new heap allocation %p",
                      elem->data);
 
                /* mark the entry as having a valid heap allocation */
                elem->flags |= ENTRY_ELEM_FLAG_HEAP;
                elem->ref = 1;
 
                /* fill the new block */
                if (elem->block != 0) {
                        ret = store_read_block(storestate, bse, elem_idx);
                } else {
                        ret = store_read_file(storestate, bse, elem_idx);
                }
        }
 
        /* free the allocation if there is a read error */
        if (ret != NSERROR_OK) {
                entry_release_alloc(elem);
        } else {
                /* update stats and setup return pointers */
                storestate->hit_size += elem->size;
 
                *data_out = elem->data;
                *datalen_out = elem->size;
        }
 
        return ret;
}
 
 
/**
 * release a previously fetched or stored memory object.
 *
 * @param[in] url The url is used as the unique primary key to invalidate.
 * @param[in] bsflags The flags to control how the object data is released.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror release(nsurl *url, enum backing_store_flags bsflags)
{
        nserror ret;
        struct store_entry *bse;
        struct store_entry_element *elem;
 
        /* check backing store is initialised */
        if (storestate == NULL) {
                return NSERROR_INIT_FAILED;
        }
 
        ret = get_store_entry(storestate, url, &bse);
        if (ret != NSERROR_OK) {
                NSLOG(netsurf, WARNING, "entry not found");
                return ret;
        }
 
        /* the entry element */
        if ((bsflags & BACKING_STORE_META) != 0) {
                elem = &bse->elem[ENTRY_ELEM_META];
        } else {
                elem = &bse->elem[ENTRY_ELEM_DATA];
        }
 
        ret = entry_release_alloc(elem);
 
        /* if the entry has previously been invalidated but had
         * allocation it must be invalidated fully now the allocation
         * has been released.
         */
        if ((ret == NSERROR_OK) &&
            ((bse->flags & ENTRY_FLAGS_INVALID) != 0)) {
                ret = invalidate_entry(storestate, bse);
        }
 
        return ret;
}
 
 
/**
 * Invalidate a source object from the backing store.
 *
 * The entry (if present in the backing store) must no longer
 * be returned as a result to the fetch or meta operations.
 *
 * @param url The url is used as the unique primary key to invalidate.
 * @return NSERROR_OK on success or error code on failure.
 */
static nserror
invalidate(nsurl *url)
{
        nserror ret;
        struct store_entry *bse;
 
        /* check backing store is initialised */
        if (storestate == NULL) {
                return NSERROR_INIT_FAILED;
        }
 
        ret = get_store_entry(storestate, url, &bse);
        if (ret != NSERROR_OK) {
                return ret;
        }
 
        return invalidate_entry(storestate, bse);
}
 
 
static struct gui_llcache_table llcache_table = {
        .initialise = initialise,
        .finalise = finalise,
        .store = store,
        .fetch = fetch,
        .invalidate = invalidate,
        .release = release,
};
 
struct gui_llcache_table *filesystem_llcache_table = &llcache_table;