dcache.c 32.6 KB
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/*
 * s3backer - FUSE-based single file backing store via Amazon S3
 * 
 * Copyright 2008-2011 Archie L. Cobbs <archie@dellroad.org>
 * 
 * This program 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; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * In addition, as a special exception, the copyright holders give
 * permission to link the code of portions of this program with the
 * OpenSSL library under certain conditions as described in each
 * individual source file, and distribute linked combinations including
 * the two.
 *
 * You must obey the GNU General Public License in all respects for all
 * of the code used other than OpenSSL. If you modify file(s) with this
 * exception, you may extend this exception to your version of the
 * file(s), but you are not obligated to do so. If you do not wish to do
 * so, delete this exception statement from your version. If you delete
 * this exception statement from all source files in the program, then
 * also delete it here.
 */

#include "s3backer.h"
#include "dcache.h"

/*
 * This file implements a simple on-disk storage area for cached blocks.
 * The file contains a header, a directory, and a data area. Each directory
 * entry indicates which block is stored in the corresponding "data slot"
 * in the data area and that block's MD5 checksum. Note the MD5 checksum is
 * the checksum of the stored data, which will differ from the actual block
 * data's MD5 if the block was compressed, encrypted, etc. when stored.
 *
 * File format:
 *
 *  [ struct file_header ]
 *  directory entry for data slot #0
 *  directory entry for data slot #1
 *  ...
 *  directory entry for data slot #N-1
 *  padding up to getpagesize()
 *  data slot #0
 *  data slot #1
 *  ...
 *  data slot #N-1
 */

/* Definitions */
#define DCACHE_SIGNATURE            0xe496f17b
#define ROUNDUP2(x, y)              (((x) + (y) - 1) & ~((y) - 1))
#define DIRECTORY_READ_CHUNK        1024

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#define HDR_SIZE(flags)             (((flags) & HDRFLG_NEW_FORMAT) == 0 ? sizeof(struct ofile_header) : sizeof(struct file_header))
#define DIR_ENTSIZE(flags)          (((flags) & HDRFLG_NEW_FORMAT) == 0 ? sizeof(struct odir_entry) : sizeof(struct dir_entry))
#define DIR_OFFSET(flags, dslot)    ((off_t)HDR_SIZE(flags) + (off_t)(dslot) * DIR_ENTSIZE(flags))
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#define DATA_OFFSET(priv, dslot)    ((off_t)(priv)->data + (off_t)(dslot) * (priv)->block_size)

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/* Bits for file_header.flags */
#define HDRFLG_NEW_FORMAT           0x00000001
#define HDRFLG_MASK                 0x00000001

/* Bits for dir_entry.flags */
#define ENTFLG_DIRTY                0x00000001
#define ENTFLG_MASK                 0x00000001

/* File header (old format) */
struct ofile_header {
    uint32_t                        signature;
    uint32_t                        header_size;
    uint32_t                        u_int_size;
    uint32_t                        s3b_block_t_size;
    uint32_t                        block_size;
    uint32_t                        data_align;
    uint32_t                        flags;
    u_int                           max_blocks;
} __attribute__ ((packed));

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/* File header */
struct file_header {
    uint32_t                        signature;
    uint32_t                        header_size;
    uint32_t                        u_int_size;
    uint32_t                        s3b_block_t_size;
    uint32_t                        block_size;
    uint32_t                        data_align;
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    uint32_t                        flags;
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    u_int                           max_blocks;
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    int32_t                         mount_token;
    uint32_t                        spare[7];           /* future expansion */
} __attribute__ ((packed));

/* One directory entry (old format) */
struct odir_entry {
    s3b_block_t                     block_num;
    u_char                          md5[MD5_DIGEST_LENGTH];
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} __attribute__ ((packed));

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/* One directory entry (new format) */
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struct dir_entry {
    s3b_block_t                     block_num;
    u_char                          md5[MD5_DIGEST_LENGTH];
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    uint32_t                        flags;
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} __attribute__ ((packed));

/* Private structure */
struct s3b_dcache {
    int                             fd;
    log_func_t                      *log;
    char                            *filename;
    void                            *zero_block;
    u_int                           block_size;
    u_int                           max_blocks;
    u_int                           num_alloc;
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    uint32_t                        flags;              /* copy of file_header.flags */
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    off_t                           data;
    u_int                           free_list_len;
    u_int                           free_list_alloc;
    s3b_block_t                     *free_list;
};

/* Internal functions */
static int s3b_dcache_write_entry(struct s3b_dcache *priv, u_int dslot, const struct dir_entry *entry);
#ifndef NDEBUG
static int s3b_dcache_entry_is_empty(struct s3b_dcache *priv, u_int dslot);
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static int s3b_dcache_entry_write_ok(struct s3b_dcache *priv, u_int dslot, s3b_block_t block_num, u_int dirty);
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static int s3b_dcache_read_entry(struct s3b_dcache *priv, u_int dslot, struct dir_entry *entryp);
#endif
static int s3b_dcache_create_file(struct s3b_dcache *priv, int *fdp, const char *filename, u_int max_blocks,
            struct file_header *headerp);
static int s3b_dcache_resize_file(struct s3b_dcache *priv, const struct file_header *header);
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static int s3b_dcache_init_free_list(struct s3b_dcache *priv, s3b_dcache_visit_t *visitor, void *arg, u_int visit_dirty);
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static int s3b_dcache_push(struct s3b_dcache *priv, u_int dslot);
static void s3b_dcache_pop(struct s3b_dcache *priv, u_int *dslotp);
static int s3b_dcache_read(struct s3b_dcache *priv, off_t offset, void *data, size_t len);
static int s3b_dcache_write(struct s3b_dcache *priv, off_t offset, const void *data, size_t len);
static int s3b_dcache_write2(struct s3b_dcache *priv, int fd, const char *filename, off_t offset, const void *data, size_t len);

/* Internal variables */
static const struct dir_entry zero_entry;

/* Public functions */

int
s3b_dcache_open(struct s3b_dcache **dcachep, log_func_t *log, const char *filename,
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  u_int block_size, u_int max_blocks, s3b_dcache_visit_t *visitor, void *arg, u_int visit_dirty)
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{
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    struct ofile_header oheader;
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    struct file_header header;
    struct s3b_dcache *priv;
    struct stat sb;
    int r;

    /* Sanity check */
    if (max_blocks == 0)
        return EINVAL;

    /* Initialize private structure */
    if ((priv = malloc(sizeof(*priv))) == NULL)
        return errno;
    memset(priv, 0, sizeof(*priv));
    priv->fd = -1;
    priv->log = log;
    priv->block_size = block_size;
    priv->max_blocks = max_blocks;
    if ((priv->filename = strdup(filename)) == NULL) {
        r = errno;
        goto fail1;
    }
    if ((priv->zero_block = calloc(1, block_size)) == NULL) {
        r = errno;
        goto fail2;
    }

    /* Create cache file if it doesn't already exist */
    if (stat(priv->filename, &sb) == -1 && errno == ENOENT) {
        (*priv->log)(LOG_NOTICE, "creating new cache file `%s' with capacity %u blocks", priv->filename, priv->max_blocks);
        if ((r = s3b_dcache_create_file(priv, &priv->fd, priv->filename, priv->max_blocks, NULL)) != 0)
            goto fail3;
        (void)close(priv->fd);
        priv->fd = -1;
    }

retry:
    /* Open cache file */
    assert(priv->fd == -1);
    if ((priv->fd = open(priv->filename, O_RDWR, 0)) == -1) {
        r = errno;
        (*priv->log)(LOG_ERR, "can't open cache file `%s': %s", priv->filename, strerror(r));
        goto fail3;
    }

    /* Get file info */
    if (fstat(priv->fd, &sb) == -1) {
        r = errno;
        goto fail4;
    }

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    /* Read in header with backward compatible support for older header format */
    if (sb.st_size < sizeof(oheader)) {
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        (*priv->log)(LOG_ERR, "invalid cache file `%s': file is truncated (size %ju < %u)",
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          priv->filename, (uintmax_t)sb.st_size, (u_int)sizeof(oheader));
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        r = EINVAL;
        goto fail4;
    }
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    if ((r = s3b_dcache_read(priv, (off_t)0, &oheader, sizeof(oheader))) != 0) {
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        (*priv->log)(LOG_ERR, "can't read cache file `%s' header: %s", priv->filename, strerror(r));
        goto fail4;
    }
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    switch (oheader.header_size) {
    case sizeof(oheader):                               /* old format */
        memset(&header, 0, sizeof(header));
        memcpy(&header, &oheader, sizeof(oheader));
        break;
    case sizeof(header):                                /* new format */
        if ((r = s3b_dcache_read(priv, (off_t)0, &header, sizeof(header))) != 0) {
            (*priv->log)(LOG_ERR, "can't read cache file `%s' header: %s", priv->filename, strerror(r));
            goto fail4;
        }
        break;
    default:
        (*priv->log)(LOG_ERR, "invalid cache file `%s': %s %d", priv->filename, "invalid header size", (int)oheader.header_size);
        r = EINVAL;
        goto fail4;
    }
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    /* Verify header - all but number of blocks */
    r = EINVAL;
    if (header.signature != DCACHE_SIGNATURE) {
        (*priv->log)(LOG_ERR, "invalid cache file `%s': wrong signature %08x != %08x",
          priv->filename, header.signature, DCACHE_SIGNATURE);
        goto fail4;
    }
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    if (header.header_size != HDR_SIZE(header.flags)) {
        (*priv->log)(LOG_ERR, "invalid cache file `%s': %s %d != %d",
          priv->filename, "invalid header size", (int)header.header_size, (int)HDR_SIZE(header.flags));
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        goto fail4;
    }
    if (header.u_int_size != sizeof(u_int)) {
        (*priv->log)(LOG_ERR, "invalid cache file `%s': created with sizeof(u_int) %u != %u",
          priv->filename, header.u_int_size, (u_int)sizeof(u_int));
        goto fail4;
    }
    if (header.s3b_block_t_size != sizeof(s3b_block_t)) {
        (*priv->log)(LOG_ERR, "invalid cache file `%s': created with sizeof(s3b_block_t) %u != %u",
          priv->filename, header.s3b_block_t_size, (u_int)sizeof(s3b_block_t));
        goto fail4;
    }
    if (header.block_size != priv->block_size) {
        (*priv->log)(LOG_ERR, "invalid cache file `%s': created with block size %u != %u",
          priv->filename, header.block_size, priv->block_size);
        goto fail4;
    }
    if (header.data_align != getpagesize()) {
        (*priv->log)(LOG_ERR, "invalid cache file `%s': created with alignment %u != %u",
          priv->filename, header.data_align, getpagesize());
        goto fail4;
    }
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    if ((header.flags & ~HDRFLG_MASK) != 0) {
        (*priv->log)(LOG_ERR, "invalid cache file `%s': %s", priv->filename, "unrecognized flags present");
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        goto fail4;
    }
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    priv->flags = header.flags;
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    /* Check number of blocks, shrinking or expanding if necessary */
    if (header.max_blocks != priv->max_blocks) {
        (*priv->log)(LOG_NOTICE, "cache file `%s' was created with capacity %u != %u blocks, automatically %s",
          priv->filename, header.max_blocks, priv->max_blocks, header.max_blocks < priv->max_blocks ?
           "expanding" : "shrinking");
        if ((r = s3b_dcache_resize_file(priv, &header)) != 0)
            goto fail4;
        (*priv->log)(LOG_INFO, "successfully resized cache file `%s' from %u to %u blocks",
          priv->filename, header.max_blocks, priv->max_blocks);
        goto retry;
    }

    /* Verify file's directory is not truncated */
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    if (sb.st_size < DIR_OFFSET(priv->flags, priv->max_blocks)) {
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        (*priv->log)(LOG_ERR, "invalid cache file `%s': file is truncated (size %ju < %ju)",
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          priv->filename, (uintmax_t)sb.st_size, (uintmax_t)DIR_OFFSET(priv->flags, priv->max_blocks));
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        goto fail4;
    }

    /* Compute offset of first data block */
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    priv->data = ROUNDUP2(DIR_OFFSET(priv->flags, priv->max_blocks), header.data_align);
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    /* Read the directory to build the free list and visit allocated blocks */
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    if (visitor != NULL && (r = s3b_dcache_init_free_list(priv, visitor, arg, visit_dirty)) != 0)
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        goto fail4;

    /* Done */
    *dcachep = priv;
    return 0;

fail4:
    close(priv->fd);
fail3:
    free(priv->zero_block);
fail2:
    free(priv->filename);
fail1:
    free(priv->free_list);
    free(priv);
    return r;
}

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int
s3b_dcache_has_mount_token(struct s3b_dcache *priv)
{
    return (priv->flags & HDRFLG_NEW_FORMAT) != 0;
}

int
s3b_dcache_set_mount_token(struct s3b_dcache *priv, int32_t *old_valuep, int32_t new_value)
{
    int r;

    /* Read old value */
    if (old_valuep != NULL) {
        if ((r = s3b_dcache_read(priv, offsetof(struct file_header, mount_token), old_valuep, sizeof(*old_valuep))) != 0)
            return r;
    }

    /* Write new value */
    if (new_value >= 0) {

        /* Update file */
        if ((r = s3b_dcache_write(priv, offsetof(struct file_header, mount_token), &new_value, sizeof(new_value))) != 0)
            return r;

        /* Sync to disk */
        s3b_dcache_fsync(priv);
    }

    /* Done */
    return 0;
}

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void
s3b_dcache_close(struct s3b_dcache *priv)
{
    close(priv->fd);
    free(priv->zero_block);
    free(priv->filename);
    free(priv->free_list);
    free(priv);
}

u_int
s3b_dcache_size(struct s3b_dcache *priv)
{
    return priv->num_alloc;
}

/*
 * Allocate a dslot for a block's data. We don't record this block in the directory yet;
 * that is done by s3b_dcache_record_block().
 */
int
s3b_dcache_alloc_block(struct s3b_dcache *priv, u_int *dslotp)
{
    /* Any free dslots? */
    if (priv->free_list_len == 0)
        return ENOMEM;

    /* Pop off the next free dslot */
    s3b_dcache_pop(priv, dslotp);

    /* Directory entry should be empty */
    assert(s3b_dcache_entry_is_empty(priv, *dslotp));

    /* Done */
    priv->num_alloc++;
    return 0;
}

/*
 * Record a block's dslot in the directory. After this function is called, the block will
 * be visible in the directory and picked up after a restart.
 *
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 * If md5 != NULL, the block is CLEAN; if md5 == NULL, the block is DIRTY.
 *
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 * This should be called AFTER the data for the block has already been written.
 *
 * There MUST NOT be a directory entry for the block.
 */
int
s3b_dcache_record_block(struct s3b_dcache *priv, u_int dslot, s3b_block_t block_num, const u_char *md5)
{
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    const u_int dirty = md5 == NULL;
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    struct dir_entry entry;
    int r;

    /* Sanity check */
    assert(dslot < priv->max_blocks);

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    /* Directory entry should be writable */
    assert(s3b_dcache_entry_write_ok(priv, dslot, block_num, dirty));

    /* If cache file is older format, it doesn't store dirty blocks, so just erase it instead (prior behavior) */
    if (dirty && (priv->flags & HDRFLG_NEW_FORMAT) == 0) {
        s3b_dcache_erase_block(priv, dslot);
        return 0;
    }
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    /* Make sure any new data is written to disk before updating the directory */
    if ((r = s3b_dcache_fsync(priv)) != 0)
        return r;

    /* Update directory */
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    memset(&entry, 0, sizeof(entry));
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    entry.block_num = block_num;
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    entry.flags = dirty ? ENTFLG_DIRTY : 0;
    if (!dirty)
        memcpy(&entry.md5, md5, MD5_DIGEST_LENGTH);
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    if ((r = s3b_dcache_write_entry(priv, dslot, &entry)) != 0)
        return r;

    /* Done */
    return 0;
}

/*
 * Erase the directory entry for a dslot. After this function is called, the block will
 * no longer be visible in the directory after a restart.
 *
 * This should be called BEFORE any new data for the block is written.
 *
 * There MUST be a directory entry for the block.
 */
int
s3b_dcache_erase_block(struct s3b_dcache *priv, u_int dslot)
{
    int r;

    /* Sanity check */
    assert(dslot < priv->max_blocks);

    /* Update directory */
    if ((r = s3b_dcache_write_entry(priv, dslot, &zero_entry)) != 0)
        return r;

    /* Make sure directory entry is written to disk before any new data is written */
    if ((r = s3b_dcache_fsync(priv)) != 0)
        return r;

    /* Done */
    return 0;
}

/*
 * Free a no-longer used dslot.
 *
 * There MUST NOT be a directory entry for the block.
 */
int
s3b_dcache_free_block(struct s3b_dcache *priv, u_int dslot)
{
    int r;

    /* Sanity check */
    assert(dslot < priv->max_blocks);

    /* Directory entry should be empty */
    assert(s3b_dcache_entry_is_empty(priv, dslot));

    /* Push dslot onto free list */
    if ((r = s3b_dcache_push(priv, dslot)) != 0)
        return r;

    /* Done */
    priv->num_alloc--;
    return 0;
}

/*
 * Read data from one dslot.
 */
int
s3b_dcache_read_block(struct s3b_dcache *priv, u_int dslot, void *dest, u_int off, u_int len)
{
    /* Sanity check */
    assert(dslot < priv->max_blocks);
    assert(off <= priv->block_size);
    assert(len <= priv->block_size);
    assert(off + len <= priv->block_size);

    /* Read data */
    return s3b_dcache_read(priv, DATA_OFFSET(priv, dslot) + off, dest, len);
}

/*
 * Write data into one dslot.
 */
int
s3b_dcache_write_block(struct s3b_dcache *priv, u_int dslot, const void *src, u_int off, u_int len)
{
    /* Sanity check */
    assert(dslot < priv->max_blocks);
    assert(off <= priv->block_size);
    assert(len <= priv->block_size);
    assert(off + len <= priv->block_size);

    /* Write data */
    return s3b_dcache_write(priv, DATA_OFFSET(priv, dslot) + off, src != NULL ? src : priv->zero_block, len);
}

/*
 * Synchronize outstanding changes to persistent storage.
 */
int
s3b_dcache_fsync(struct s3b_dcache *priv)
{
    int r;

#if HAVE_DECL_FDATASYNC
    r = fdatasync(priv->fd);
#else
    r = fsync(priv->fd);
#endif
    if (r == -1) {
        r = errno;
        (*priv->log)(LOG_ERR, "error fsync'ing cache file `%s': %s", priv->filename, strerror(r));
    }
    return 0;
}

/* Internal functions */

#ifndef NDEBUG
static int
s3b_dcache_entry_is_empty(struct s3b_dcache *priv, u_int dslot)
{
    struct dir_entry entry;

    (void)s3b_dcache_read_entry(priv, dslot, &entry);
    return memcmp(&entry, &zero_entry, sizeof(entry)) == 0;
}

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static int
s3b_dcache_entry_write_ok(struct s3b_dcache *priv, u_int dslot, s3b_block_t block_num, u_int dirty)
{
    struct dir_entry entry;
    u_int old_dirty;

    if (s3b_dcache_entry_is_empty(priv, dslot))
        return 1;
    (void)s3b_dcache_read_entry(priv, dslot, &entry);
    old_dirty = (entry.flags & ENTFLG_DIRTY) != 0;
    return entry.block_num == block_num && old_dirty != dirty;
}

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static int
s3b_dcache_read_entry(struct s3b_dcache *priv, u_int dslot, struct dir_entry *entry)
{
    assert(dslot < priv->max_blocks);
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    memset(entry, 0, sizeof(*entry));
    return s3b_dcache_read(priv, DIR_OFFSET(priv->flags, dslot), entry, DIR_ENTSIZE(priv->flags));
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}
#endif

/*
 * Write a directory entry.
 */
static int
s3b_dcache_write_entry(struct s3b_dcache *priv, u_int dslot, const struct dir_entry *entry)
{
    assert(dslot < priv->max_blocks);
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    assert((entry->flags & ~((priv->flags & HDRFLG_NEW_FORMAT) != 0 ? ENTFLG_MASK : 0)) == 0);
    return s3b_dcache_write(priv, DIR_OFFSET(priv->flags, dslot), entry, DIR_ENTSIZE(priv->flags));
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}

/*
 * Resize (and compress) an existing cache file. Upon successful return, priv->fd is closed
 * and the cache file must be re-opened.
 */
static int
s3b_dcache_resize_file(struct s3b_dcache *priv, const struct file_header *old_header)
{
    const u_int old_max_blocks = old_header->max_blocks;
    const u_int new_max_blocks = priv->max_blocks;
    struct file_header new_header;
    off_t old_data_base;
    off_t new_data_base;
    u_int base_old_dslot;
    u_int new_dslot = 0;
    u_int num_entries;
    u_char *block_buf = NULL;
    char *tempfile = NULL;
    int new_fd = -1;
    int r;

    /* Create new temporary cache file */
    if (asprintf(&tempfile, "%s.new", priv->filename) == -1) {
        r = errno;
        tempfile = NULL;
        (*priv->log)(LOG_ERR, "can't allocate string: %s", strerror(r));
        goto fail;
    }
    if ((r = s3b_dcache_create_file(priv, &new_fd, tempfile, new_max_blocks, &new_header)) != 0)
        goto fail;

    /* Allocate block data buffer */
    if ((block_buf = malloc(priv->block_size)) == NULL) {
        r = errno;
        (*priv->log)(LOG_ERR, "can't allocate buffer: %s", strerror(r));
        goto fail;
    }

    /* Copy non-empty cache entries from old file to new file */
624 625
    old_data_base = ROUNDUP2(DIR_OFFSET(old_header->flags, old_max_blocks), old_header->data_align);
    new_data_base = ROUNDUP2(DIR_OFFSET(new_header.flags, new_max_blocks), new_header.data_align);
626
    for (base_old_dslot = 0; base_old_dslot < old_max_blocks; base_old_dslot += num_entries) {
627
        char buffer[DIRECTORY_READ_CHUNK * DIR_ENTSIZE(old_header->flags)];
628 629 630 631 632 633
        int i;

        /* Read in the next chunk of old directory entries */
        num_entries = old_max_blocks - base_old_dslot;
        if (num_entries > DIRECTORY_READ_CHUNK)
            num_entries = DIRECTORY_READ_CHUNK;
634 635
        if ((r = s3b_dcache_read(priv, DIR_OFFSET(old_header->flags, base_old_dslot),
          buffer, num_entries * DIR_ENTSIZE(old_header->flags))) != 0) {
636 637 638 639 640 641 642
            (*priv->log)(LOG_ERR, "error reading cache file `%s' directory: %s", priv->filename, strerror(r));
            goto fail;
        }

        /* For each dslot: if not free, copy it to the next slot in the new file */
        for (i = 0; i < num_entries; i++) {
            const u_int old_dslot = base_old_dslot + i;
643
            struct dir_entry entry;
644 645 646
            off_t old_data;
            off_t new_data;

647 648 649 650
            /* Read old entry */
            memset(&entry, 0, sizeof(entry));
            memcpy(&entry, buffer + i * DIR_ENTSIZE(old_header->flags), DIR_ENTSIZE(old_header->flags));

651
            /* Is this entry non-empty? */
652
            if (memcmp(&entry, &zero_entry, sizeof(entry)) == 0)
653 654 655 656 657 658 659 660 661 662
                continue;

            /* Any more space? */
            if (new_dslot == new_max_blocks) {
                (*priv->log)(LOG_INFO, "cache file `%s' contains more than %u blocks; some will be discarded",
                  priv->filename, new_max_blocks);
                goto done;
            }

            /* Copy the directory entry */
663 664 665
            assert(DIR_ENTSIZE(new_header.flags) == sizeof(entry));
            if ((r = s3b_dcache_write2(priv, new_fd, tempfile,
              DIR_OFFSET(new_header.flags, new_dslot), &entry, sizeof(entry))) != 0)
666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697
                goto fail;

            /* Copy the data block */
            old_data = old_data_base + (off_t)old_dslot * priv->block_size;
            new_data = new_data_base + (off_t)new_dslot * priv->block_size;
            if ((r = s3b_dcache_read(priv, old_data, block_buf, priv->block_size)) != 0)
                goto fail;
            if ((r = s3b_dcache_write2(priv, new_fd, tempfile, new_data, block_buf, priv->block_size)) != 0)
                goto fail;

            /* Advance to the next slot */
            new_dslot++;
        }
    }

done:
    /* Close the new file */
    if (close(new_fd) == -1) {
        (*priv->log)(LOG_ERR, "error closing temporary cache file `%s': %s", tempfile, strerror(r));
        goto fail;
    }
    new_fd = -1;

    /* Replace old cache file with new cache file */
    if (rename(tempfile, priv->filename) == -1) {
        r = errno;
        (*priv->log)(LOG_ERR, "error renaming `%s' to `%s': %s", tempfile, priv->filename, strerror(r));
        goto fail;
    }
    free(tempfile);
    tempfile = NULL;

698 699 700
    /* Update flags */
    priv->flags = new_header.flags;

701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727
    /* Close old file to release it and we're done */
    close(priv->fd);
    priv->fd = -1;
    r = 0;

fail:
    /* Clean up */
    if (block_buf != NULL)
        free(block_buf);
    if (new_fd != -1)
        (void)close(new_fd);
    if (tempfile != NULL) {
        (void)unlink(tempfile);
        free(tempfile);
    }
    return r;
}

static int
s3b_dcache_create_file(struct s3b_dcache *priv, int *fdp, const char *filename, u_int max_blocks, struct file_header *headerp)
{
    struct file_header header;
    int r;

    /* Initialize header */
    memset(&header, 0, sizeof(header));
    header.signature = DCACHE_SIGNATURE;
728 729
    header.flags = HDRFLG_NEW_FORMAT;
    header.header_size = HDR_SIZE(header.flags);
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    header.u_int_size = sizeof(u_int);
    header.s3b_block_t_size = sizeof(s3b_block_t);
    header.block_size = priv->block_size;
    header.max_blocks = priv->max_blocks;
    header.data_align = getpagesize();

    /* Create file */
    if ((*fdp = open(filename, O_RDWR|O_CREAT|O_EXCL, 0644)) == -1) {
        r = errno;
        (*priv->log)(LOG_ERR, "can't create file `%s': %s", filename, strerror(r));
        return r;
    }

    /* Write header */
    if ((r = s3b_dcache_write2(priv, *fdp, filename, (off_t)0, &header, sizeof(header))) != 0) {
        (*priv->log)(LOG_ERR, "error initializing cache file `%s': %s", filename, strerror(r));
        goto fail;
    }

    /* Extend the file to the required length; the directory will be filled with zeroes */
750
    if (ftruncate(*fdp, sizeof(header)) == -1 || ftruncate(*fdp, DIR_OFFSET(header.flags, max_blocks)) == -1) {
751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768
        r = errno;
        (*priv->log)(LOG_ERR, "error initializing cache file `%s': %s", filename, strerror(r));
        goto fail;
    }

    /* Done */
    if (headerp != NULL)
        *headerp = header;
    return 0;

fail:
    (void)unlink(filename);
    (void)close(*fdp);
    *fdp = -1;
    return r;
}

static int
769
s3b_dcache_init_free_list(struct s3b_dcache *priv, s3b_dcache_visit_t *visitor, void *arg, u_int visit_dirty)
770 771 772 773 774 775 776 777 778 779 780
{
    off_t required_size;
    struct stat sb;
    u_int num_entries;
    u_int num_dslots_used;
    u_int base_dslot;
    u_int i;
    int r;

    /* Logging */
    (*priv->log)(LOG_INFO, "reading meta-data from cache file `%s'", priv->filename);
781
    assert(visitor != NULL);
782 783 784

    /* Inspect all directory entries */
    for (num_dslots_used = base_dslot = 0; base_dslot < priv->max_blocks; base_dslot += num_entries) {
785
        char buffer[DIRECTORY_READ_CHUNK * DIR_ENTSIZE(priv->flags)];
786 787 788 789 790

        /* Read in the next chunk of directory entries */
        num_entries = priv->max_blocks - base_dslot;
        if (num_entries > DIRECTORY_READ_CHUNK)
            num_entries = DIRECTORY_READ_CHUNK;
791
        if ((r = s3b_dcache_read(priv, DIR_OFFSET(priv->flags, base_dslot), buffer, num_entries * DIR_ENTSIZE(priv->flags))) != 0) {
792 793 794 795
            (*priv->log)(LOG_ERR, "error reading cache file `%s' directory: %s", priv->filename, strerror(r));
            return r;
        }

796
        /* For each dslot: if free, add to the free list, else let visitor decide what to do */
797 798
        for (i = 0; i < num_entries; i++) {
            const u_int dslot = base_dslot + i;
799
            struct dir_entry entry;
800

801 802 803 804 805 806 807 808
            memset(&entry, 0, sizeof(entry));
            memcpy(&entry, buffer + i * DIR_ENTSIZE(priv->flags), DIR_ENTSIZE(priv->flags));
            if (memcmp(&entry, &zero_entry, sizeof(entry)) == 0) {
                if ((r = s3b_dcache_push(priv, dslot)) != 0)
                    return r;
            } else if ((entry.flags & ENTFLG_DIRTY) != 0 && !visit_dirty) {     /* visitor doesn't want dirties, so just nuke it */
                if ((r = s3b_dcache_write_entry(priv, dslot, &zero_entry)) != 0)
                    return r;
809 810 811
                if ((r = s3b_dcache_push(priv, dslot)) != 0)
                    return r;
            } else {
812
                priv->num_alloc++;
813 814
                if (dslot + 1 > num_dslots_used)                    /* keep track of the number of dslots in use */
                    num_dslots_used = dslot + 1;
815
                if ((r = (*visitor)(arg, dslot, entry.block_num, (entry.flags & ENTFLG_DIRTY) == 0 ? entry.md5 : NULL)) != 0)
816 817 818 819 820 821 822 823 824 825 826 827 828 829
                    return r;
            }
        }
    }

    /* Reverse the free list so we allocate lower numbered slots first */
    for (i = 0; i < priv->free_list_len / 2; i++) {
        const s3b_block_t temp = priv->free_list[i];

        priv->free_list[i] = priv->free_list[priv->free_list_len - i - 1];
        priv->free_list[priv->free_list_len - i - 1] = temp;
    }

    /* Verify the cache file is not truncated */
830
    required_size = DIR_OFFSET(priv->flags, priv->max_blocks);
831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969
    if (num_dslots_used > 0) {
        if (required_size < DATA_OFFSET(priv, num_dslots_used))
            required_size = DATA_OFFSET(priv, num_dslots_used);
    }
    if (fstat(priv->fd, &sb) == -1) {
        r = errno;
        (*priv->log)(LOG_ERR, "error reading cache file `%s' length: %s", priv->filename, strerror(r));
        return r;
    }
    if (sb.st_size < required_size) {
        (*priv->log)(LOG_ERR, "cache file `%s' is truncated (has size %ju < %ju bytes)",
          priv->filename, (uintmax_t)sb.st_size, (uintmax_t)required_size);
        return EINVAL;
    }

    /* Discard any unreferenced data beyond the last entry */
    if (sb.st_size > required_size && ftruncate(priv->fd, required_size) == -1) {
        r = errno;
        (*priv->log)(LOG_ERR, "error trimming cache file `%s' to %ju bytes: %s",
          priv->filename, (uintmax_t)required_size, strerror(r));
        return EINVAL;
    }

    /* Report results */
    (*priv->log)(LOG_INFO, "loaded cache file `%s' with %u free and %u used blocks (max index %u)",
      priv->filename, priv->free_list_len, priv->max_blocks - priv->free_list_len, num_dslots_used);

    /* Done */
    return 0;
}

/*
 * Push a dslot onto the free list.
 */
static int
s3b_dcache_push(struct s3b_dcache *priv, u_int dslot)
{
    /* Sanity check */
    assert(dslot < priv->max_blocks);
    assert(priv->free_list_len < priv->max_blocks);

    /* Grow the free list array if necessary */
    if (priv->free_list_alloc == priv->free_list_len) {
        s3b_block_t *new_free_list;
        s3b_block_t new_free_list_alloc;
        int r;

        new_free_list_alloc = priv->free_list_alloc == 0 ? 1024 : 2 * priv->free_list_alloc;
        if ((new_free_list = realloc(priv->free_list, new_free_list_alloc * sizeof(*new_free_list))) == NULL) {
            r = errno;
            (*priv->log)(LOG_ERR, "realloc: %s", strerror(r));
            return r;
        }
        priv->free_list = new_free_list;
        priv->free_list_alloc = new_free_list_alloc;
    }

    /* Add new dslot */
    assert(priv->free_list_len < priv->free_list_alloc);
    priv->free_list[priv->free_list_len++] = dslot;
    return 0;
}

/*
 * Pop the next dslot off of the free list. There must be one.
 */
static void
s3b_dcache_pop(struct s3b_dcache *priv, u_int *dslotp)
{
    /* Sanity check */
    assert(priv->free_list_len > 0);

    /* Pop off dslot at the head of the list */
    *dslotp = priv->free_list[--priv->free_list_len];
    assert(*dslotp < priv->max_blocks);

    /* See if we can give back some memory */
    if (priv->free_list_alloc > 1024 && priv->free_list_len <= priv->free_list_alloc / 4) {
        s3b_block_t *new_free_list;
        s3b_block_t new_free_list_alloc;

        new_free_list_alloc = priv->free_list_alloc / 4;
        if ((new_free_list = realloc(priv->free_list, new_free_list_alloc * sizeof(*new_free_list))) == NULL)
            (*priv->log)(LOG_ERR, "can't shrink dcache free list: realloc: %s (ignored)", strerror(errno));
        else {
            priv->free_list = new_free_list;
            priv->free_list_alloc = new_free_list_alloc;
        }
    }
    assert(priv->free_list_len <= priv->free_list_alloc);
}

static int
s3b_dcache_read(struct s3b_dcache *priv, off_t offset, void *data, size_t len)
{
    size_t sofar;
    ssize_t r;

    for (sofar = 0; sofar < len; sofar += r) {
        const off_t posn = offset + sofar;

        if ((r = pread(priv->fd, (char *)data + sofar, len - sofar, offset + sofar)) == -1) {
            (*priv->log)(LOG_ERR, "error reading cache file `%s' at offset %ju: %s",
              priv->filename, (uintmax_t)posn, strerror(r));
            return r;
        }
        if (r == 0) {           /* truncated input */
            (*priv->log)(LOG_ERR, "error reading cache file `%s' at offset %ju: file is truncated",
              priv->filename, (uintmax_t)posn);
            return EINVAL;
        }
    }
    return 0;
}

static int
s3b_dcache_write(struct s3b_dcache *priv, off_t offset, const void *data, size_t len)
{
    return s3b_dcache_write2(priv, priv->fd, priv->filename, offset, data, len);
}

static int
s3b_dcache_write2(struct s3b_dcache *priv, int fd, const char *filename, off_t offset, const void *data, size_t len)
{
    size_t sofar;
    ssize_t r;

    for (sofar = 0; sofar < len; sofar += r) {
        const off_t posn = offset + sofar;

        if ((r = pwrite(fd, (const char *)data + sofar, len - sofar, offset + sofar)) == -1) {
            (*priv->log)(LOG_ERR, "error writing cache file `%s' at offset %ju: %s",
              filename, (uintmax_t)posn, strerror(r));
            return r;
        }
    }
    return 0;
}