src/lib-index/mail-cache.c

	mail-cache.c revision 5bd1c1d4fe3265d5e6b6054044fd6d78e42c9d0a
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi/* Copyright (c) 2003-2016 Dovecot authors, see the included COPYING file */
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "lib.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "array.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "buffer.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "hash.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "nfs-workarounds.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "file-cache.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "mmap-util.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "read-full.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include "write-full.h"
28f2ab26ea78e929253e38c6e87bb0e3c05112f2KATOH Yasufumi#include "mail-cache-private.h"
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi#include <unistd.h>
b0e26ca77b3bb9908dda4a27504e805f1b8b5ee0KATOH Yasufumi
3220ecebfc2822a55b9848b002a5495d30f479b9KATOH Yasufumi#define MAIL_CACHE_MIN_HEADER_READ_SIZE 4096
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
842948e4162d89ffce0e8cd292702598d736489aKATOH Yasufumivoid mail_cache_set_syscall_error(struct mail_cache *cache,
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi                  const char *function)
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi{
da1f8f26b5bb2393c9dcd36b7761f3cfa1204e36Stéphane Graber    mail_index_file_set_syscall_error(cache->index, cache->filepath,
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi                      function);
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi}
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
94891ea3e44961f4369a7cc67d38c3a98a0e4c54Stéphane Graberstatic void mail_cache_unlink(struct mail_cache *cache)
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi{
ebe0aeb19cff9539bd749107d245874774d8a371KATOH Yasufumi    if (!cache->index->readonly)
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi        i_unlink(cache->filepath);
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi}
be54cb1c55806073b5a08a99b991b1f9a2a2cef0KATOH Yasufumi
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumivoid mail_cache_reset(struct mail_cache *cache)
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi{
07ece60087c22f03fac080edad21a2620d5737efKATOH Yasufumi    mail_cache_unlink(cache);
755d8d03b148a0ada1ec93e4701edea0a92a4705KATOH Yasufumi    /* mark the cache as unusable */
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    cache->hdr = NULL;
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi}
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
fb261f53fcad6a04473172c9c9b68ae1cc5afc7bKATOH Yasufumivoid mail_cache_set_corrupted(struct mail_cache *cache, const char *fmt, ...)
fb261f53fcad6a04473172c9c9b68ae1cc5afc7bKATOH Yasufumi{
07ece60087c22f03fac080edad21a2620d5737efKATOH Yasufumi    va_list va;
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    mail_cache_reset(cache);
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
d0a6bd39400a6d14cfec94ad647f3af1bda1e321Christian Brauner    va_start(va, fmt);
d0a6bd39400a6d14cfec94ad647f3af1bda1e321Christian Brauner    T_BEGIN {
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi        mail_index_set_error(cache->index,
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi                     "Corrupted index cache file %s: %s",
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi                     cache->filepath,
d0a6bd39400a6d14cfec94ad647f3af1bda1e321Christian Brauner                     t_strdup_vprintf(fmt, va));
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    } T_END;
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    va_end(va);
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi}
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumivoid mail_cache_file_close(struct mail_cache *cache)
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi{
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    if (cache->mmap_base != NULL) {
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi        if (munmap(cache->mmap_base, cache->mmap_length) < 0)
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi            mail_cache_set_syscall_error(cache, "munmap()");
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    }
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    if (cache->file_cache != NULL)
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi        file_cache_set_fd(cache->file_cache, -1);
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    if (cache->read_buf != NULL)
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi        buffer_set_used_size(cache->read_buf, 0);
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    cache->mmap_base = NULL;
57da8c32f85c0255efa61ee32e260068afdaa565KATOH Yasufumi    cache->hdr = NULL;
    cache->mmap_length = 0;
    cache->last_field_header_offset = 0;

    if (cache->file_lock != NULL)
        file_lock_free(&cache->file_lock);
    cache->locked = FALSE;

    if (cache->fd != -1) {
        if (close(cache->fd) < 0)
            mail_cache_set_syscall_error(cache, "close()");
        cache->fd = -1;
    }
}

static void mail_cache_init_file_cache(struct mail_cache *cache)
{
    struct stat st;

    if (cache->file_cache != NULL)
        file_cache_set_fd(cache->file_cache, cache->fd);

    if (fstat(cache->fd, &st) == 0) {
        if (cache->file_cache != NULL)
            (void)file_cache_set_size(cache->file_cache, st.st_size);
    } else if (!ESTALE_FSTAT(errno)) {
        mail_cache_set_syscall_error(cache, "fstat()");
    }

    cache->st_ino = st.st_ino;
    cache->st_dev = st.st_dev;
}

static int mail_cache_try_open(struct mail_cache *cache)
{
    const void *data;

    cache->opened = TRUE;

    if (MAIL_INDEX_IS_IN_MEMORY(cache->index))
        return 0;

    cache->fd = nfs_safe_open(cache->filepath,
                  cache->index->readonly ? O_RDONLY : O_RDWR);
    if (cache->fd == -1) {
        if (errno == ENOENT) {
            cache->need_compress_file_seq = 0;
            return 0;
        }

        mail_cache_set_syscall_error(cache, "open()");
        return -1;
    }

    mail_cache_init_file_cache(cache);

    if (mail_cache_map(cache, 0, 0, &data) < 0)
        return -1;
    return 1;
}

static bool mail_cache_need_reopen(struct mail_cache *cache)
{
    struct stat st;

    if (MAIL_CACHE_IS_UNUSABLE(cache)) {
        if (cache->need_compress_file_seq != 0) {
            /* we're waiting for compression */
            return FALSE;
        }
        if (MAIL_INDEX_IS_IN_MEMORY(cache->index)) {
            /* disabled */
            return FALSE;
        }
    }

    if (cache->fd == -1)
        return TRUE;

    /* see if the file has changed */
    if ((cache->index->flags & MAIL_INDEX_OPEN_FLAG_NFS_FLUSH) != 0) {
        i_assert(!cache->locked);
        nfs_flush_file_handle_cache(cache->filepath);
    }
    if (nfs_safe_stat(cache->filepath, &st) < 0) {
        mail_cache_set_syscall_error(cache, "stat()");
        return TRUE;
    }

    if (st.st_ino != cache->st_ino ||
        !CMP_DEV_T(st.st_dev, cache->st_dev)) {
        /* file changed */
        return TRUE;
    }

    if ((cache->index->flags & MAIL_INDEX_OPEN_FLAG_NFS_FLUSH) != 0) {
        /* if the old file has been deleted, the new file may have
           the same inode as the old one. we'll catch this here by
           checking if fstat() fails with ESTALE */
        if (fstat(cache->fd, &st) < 0) {
            if (ESTALE_FSTAT(errno))
                return TRUE;
            mail_cache_set_syscall_error(cache, "fstat()");
            return FALSE;
        }
    }
    return FALSE;
}

static int mail_cache_reopen_now(struct mail_cache *cache)
{
    struct mail_index_view *view;
    const struct mail_index_ext *ext;

    mail_cache_file_close(cache);

    if (mail_cache_try_open(cache) <= 0)
        return -1;

    if (mail_cache_header_fields_read(cache) < 0)
        return -1;

    view = mail_index_view_open(cache->index);
    ext = mail_index_view_get_ext(view, cache->ext_id);
    if (ext == NULL || cache->hdr->file_seq != ext->reset_id) {
        /* still different - maybe a race condition or maybe the
           file_seq really is corrupted. either way, this shouldn't
           happen often so we'll just mark cache to be compressed
           later which fixes this. */
        cache->need_compress_file_seq = cache->hdr->file_seq;
        mail_index_view_close(&view);
        return 0;
    }

    mail_index_view_close(&view);
    i_assert(!MAIL_CACHE_IS_UNUSABLE(cache));
    return 1;
}

int mail_cache_reopen(struct mail_cache *cache)
{
    i_assert(!cache->locked);

    if (!mail_cache_need_reopen(cache)) {
        /* reopening does no good */
        return 0;
    }
    return mail_cache_reopen_now(cache);
}

static void mail_cache_update_need_compress(struct mail_cache *cache)
{
    const struct mail_cache_header *hdr = cache->hdr;
    struct stat st;
    unsigned int msg_count;
    unsigned int records_count, cont_percentage, delete_percentage;
    bool want_compress = FALSE;

    if (hdr->minor_version == 0) {
        /* compress to get ourself into the new header version */
        cache->need_compress_file_seq = hdr->file_seq;
        return;
    }

    msg_count = cache->index->map->rec_map->records_count;
    if (msg_count == 0)
        records_count = 1;
    else if (hdr->record_count == 0 || hdr->record_count > msg_count*2) {
        /* probably not the real record_count, but hole offset that
           Dovecot <=v2.1 versions used to use in this position.
           we already checked that minor_version>0, but this could
           happen if old Dovecot was used to access mailbox after
           it had been updated. */
        records_count = I_MAX(msg_count, 1);
        cache->hdr_copy.record_count = msg_count;
        cache->hdr_modified = TRUE;
    } else {
        records_count = hdr->record_count;
    }

    cont_percentage = hdr->continued_record_count * 100 / records_count;
    if (cont_percentage >= MAIL_CACHE_COMPRESS_CONTINUED_PERCENTAGE) {
        /* too many continued rows, compress */
        want_compress = TRUE;
    }

    delete_percentage = hdr->deleted_record_count * 100 /
        (records_count + hdr->deleted_record_count);
    if (delete_percentage >= MAIL_CACHE_COMPRESS_DELETE_PERCENTAGE) {
        /* too many deleted records, compress */
        want_compress = TRUE;
    }

    if (want_compress) {
        if (fstat(cache->fd, &st) < 0) {
            if (!ESTALE_FSTAT(errno))
                mail_cache_set_syscall_error(cache, "fstat()");
            return;
        }
        if (st.st_size >= MAIL_CACHE_COMPRESS_MIN_SIZE)
            cache->need_compress_file_seq = hdr->file_seq;
    }

}

static bool mail_cache_verify_header(struct mail_cache *cache,
                     const struct mail_cache_header *hdr)
{
    /* check that the header is still ok */
    if (cache->mmap_length < sizeof(struct mail_cache_header)) {
        mail_cache_set_corrupted(cache, "File too small");
        return FALSE;
    }

    if (hdr->major_version != MAIL_CACHE_MAJOR_VERSION) {
        /* version changed - upgrade silently */
        mail_cache_unlink(cache);
        return FALSE;
    }
    if (hdr->compat_sizeof_uoff_t != sizeof(uoff_t)) {
        /* architecture change - handle silently(?) */
        mail_cache_unlink(cache);
        return FALSE;
    }

    if (hdr->indexid != cache->index->indexid) {
        /* index id changed - handle silently */
        mail_cache_unlink(cache);
        return FALSE;
    }
    if (hdr->file_seq == 0) {
        mail_cache_set_corrupted(cache, "file_seq is 0");
        return FALSE;
    }
    return TRUE;
}

static int
mail_cache_map_finish(struct mail_cache *cache, uoff_t offset, size_t size,
              const void *hdr_data, bool copy_hdr)
{
    const struct mail_cache_header *hdr = hdr_data;

    if (offset == 0) {
        /* verify the header validity only with offset=0. this way
           we won't waste time re-verifying it all the time */
        if (!mail_cache_verify_header(cache, hdr)) {
            cache->need_compress_file_seq =
                !MAIL_CACHE_IS_UNUSABLE(cache) &&
                cache->hdr->file_seq != 0 ?
                cache->hdr->file_seq : 0;
            cache->hdr = NULL;
            return -1;
        }
    }
    if (hdr_data != NULL) {
        if (!copy_hdr)
            cache->hdr = hdr;
        else {
            memcpy(&cache->hdr_ro_copy, hdr,
                   sizeof(cache->hdr_ro_copy));
            cache->hdr = &cache->hdr_ro_copy;
        }
        mail_cache_update_need_compress(cache);
    } else {
        i_assert(cache->hdr != NULL);
    }
    i_assert(cache->hdr->file_seq != 0);

    if (offset + size > cache->mmap_length)
        return 0;
    return 1;
}

static int
mail_cache_map_with_read(struct mail_cache *cache, size_t offset, size_t size,
             const void **data_r)
{
    const void *hdr_data;
    void *data;
    ssize_t ret;

    if (cache->read_buf == NULL) {
        cache->read_buf =
            buffer_create_dynamic(default_pool, size);
    } else if (cache->read_offset <= offset &&
           cache->read_offset + cache->read_buf->used >= offset+size) {
        /* already mapped */
        *data_r = CONST_PTR_OFFSET(cache->read_buf->data,
                       offset - cache->read_offset);
        hdr_data = offset == 0 ? *data_r : NULL;
        return mail_cache_map_finish(cache, offset, size, hdr_data, TRUE);
    } else {
        buffer_set_used_size(cache->read_buf, 0);
    }
    if (offset == 0 && size < MAIL_CACHE_MIN_HEADER_READ_SIZE) {
        /* we can usually read the fields header after the cache
           header. we need them both, so try to read them all with one
           pread() call. */
        size = MAIL_CACHE_MIN_HEADER_READ_SIZE;
    }

    data = buffer_append_space_unsafe(cache->read_buf, size);
    ret = pread(cache->fd, data, size, offset);
    if (ret < 0) {
        if (errno != ESTALE)
            mail_cache_set_syscall_error(cache, "read()");

        buffer_set_used_size(cache->read_buf, 0);
        cache->hdr = NULL;
        cache->mmap_length = 0;
        return -1;
    }
    buffer_set_used_size(cache->read_buf, ret);

    cache->read_offset = offset;
    cache->mmap_length = offset + cache->read_buf->used;

    *data_r = data;
    hdr_data = offset == 0 ? *data_r : NULL;
    return mail_cache_map_finish(cache, offset,
                     cache->read_buf->used, hdr_data, TRUE);
}

int mail_cache_map(struct mail_cache *cache, size_t offset, size_t size,
           const void **data_r)
{
    struct stat st;
    const void *data;
    ssize_t ret;

    if (size == 0)
        size = sizeof(struct mail_cache_header);

    /* verify offset + size before trying to allocate a huge amount of
       memory due to them. note that we may be prefetching more than we
       actually need, so don't fail too early. */
    if ((size > cache->mmap_length || offset + size > cache->mmap_length) &&
        (offset > 0 || size > sizeof(struct mail_cache_header))) {
        if (fstat(cache->fd, &st) < 0) {
            i_error("fstat(%s) failed: %m", cache->filepath);
            return -1;
        }
        if (offset >= (uoff_t)st.st_size) {
            *data_r = NULL;
            return 0;
        }
        if (offset + size > (uoff_t)st.st_size)
            size = st.st_size - offset;
    }

    cache->remap_counter++;
    if (cache->map_with_read)
        return mail_cache_map_with_read(cache, offset, size, data_r);

    if (cache->file_cache != NULL) {
        ret = file_cache_read(cache->file_cache, offset, size);
        if (ret < 0) {
                        /* In case of ESTALE we'll simply fail without error
                           messages. The caller will then just have to
                           fallback to generating the value itself.

                           We can't simply reopen the cache flie, because
                           using it requires also having updated file
                           offsets. */
                        if (errno != ESTALE)
                                mail_cache_set_syscall_error(cache, "read()");
            cache->hdr = NULL;
            return -1;
        }

        data = file_cache_get_map(cache->file_cache,
                      &cache->mmap_length);
        *data_r = offset > cache->mmap_length ? NULL :
            CONST_PTR_OFFSET(data, offset);
        return mail_cache_map_finish(cache, offset, size,
                         offset == 0 ? data : NULL, TRUE);
    }

    if (offset < cache->mmap_length &&
        size <= cache->mmap_length - offset) {
        /* already mapped */
        i_assert(cache->mmap_base != NULL);
        *data_r = CONST_PTR_OFFSET(cache->mmap_base, offset);
        return 1;
    }

    if (cache->mmap_base != NULL) {
        if (munmap(cache->mmap_base, cache->mmap_length) < 0)
            mail_cache_set_syscall_error(cache, "munmap()");
    } else {
        if (cache->fd == -1) {
            /* unusable, waiting for compression or
               index is in memory */
            i_assert(cache->need_compress_file_seq != 0 ||
                 MAIL_INDEX_IS_IN_MEMORY(cache->index));
            return -1;
        }
    }

    /* map the whole file */
    cache->hdr = NULL;
    cache->mmap_length = 0;
    if (cache->read_buf != NULL)
        buffer_set_used_size(cache->read_buf, 0);

    cache->mmap_base = mmap_ro_file(cache->fd, &cache->mmap_length);
    if (cache->mmap_base == MAP_FAILED) {
        cache->mmap_base = NULL;
        cache->mmap_length = 0;
        mail_cache_set_syscall_error(cache, "mmap()");
        return -1;
    }
    *data_r = offset > cache->mmap_length ? NULL :
        CONST_PTR_OFFSET(cache->mmap_base, offset);
    return mail_cache_map_finish(cache, offset, size,
                     cache->mmap_base, FALSE);
}

int mail_cache_open_and_verify(struct mail_cache *cache)
{
    int ret;

    ret = mail_cache_try_open(cache);
    if (ret > 0)
        ret = mail_cache_header_fields_read(cache);
    if (ret < 0) {
        /* failed for some reason - doesn't really matter,
           it's disabled for now. */
        mail_cache_file_close(cache);
    }
    return ret;
}

static struct mail_cache *mail_cache_alloc(struct mail_index *index)
{
    struct mail_cache *cache;

    cache = i_new(struct mail_cache, 1);
    cache->index = index;
    cache->fd = -1;
    cache->filepath =
        i_strconcat(index->filepath, MAIL_CACHE_FILE_SUFFIX, NULL);
    cache->field_pool = pool_alloconly_create("Cache fields", 2048);
    hash_table_create(&cache->field_name_hash, cache->field_pool, 0,
              strcase_hash, strcasecmp);

    cache->dotlock_settings.use_excl_lock =
        (index->flags & MAIL_INDEX_OPEN_FLAG_DOTLOCK_USE_EXCL) != 0;
    cache->dotlock_settings.nfs_flush =
        (index->flags & MAIL_INDEX_OPEN_FLAG_NFS_FLUSH) != 0;
    cache->dotlock_settings.timeout =
        I_MIN(MAIL_CACHE_LOCK_TIMEOUT, index->max_lock_timeout_secs);
    cache->dotlock_settings.stale_timeout = MAIL_CACHE_LOCK_CHANGE_TIMEOUT;

    if (!MAIL_INDEX_IS_IN_MEMORY(index) &&
        (index->flags & MAIL_INDEX_OPEN_FLAG_MMAP_DISABLE) != 0)
        cache->file_cache = file_cache_new(-1);
    cache->map_with_read =
        (cache->index->flags & MAIL_INDEX_OPEN_FLAG_SAVEONLY) != 0;

    cache->ext_id =
        mail_index_ext_register(index, "cache", 0,
                    sizeof(uint32_t), sizeof(uint32_t));
    mail_index_register_expunge_handler(index, cache->ext_id, FALSE,
                        mail_cache_expunge_handler, cache);
    return cache;
}

struct mail_cache *mail_cache_open_or_create(struct mail_index *index)
{
    struct mail_cache *cache;

    cache = mail_cache_alloc(index);
    return cache;
}

void mail_cache_free(struct mail_cache **_cache)
{
    struct mail_cache *cache = *_cache;

    *_cache = NULL;
    if (cache->file_cache != NULL)
        file_cache_free(&cache->file_cache);

    mail_index_unregister_expunge_handler(cache->index, cache->ext_id);
    mail_cache_file_close(cache);

    if (cache->read_buf != NULL)
        buffer_free(&cache->read_buf);
    hash_table_destroy(&cache->field_name_hash);
    pool_unref(&cache->field_pool);
    i_free(cache->field_file_map);
    i_free(cache->file_field_map);
    i_free(cache->fields);
    i_free(cache->filepath);
    i_free(cache);
}

static int mail_cache_lock_file(struct mail_cache *cache, bool nonblock)
{
    unsigned int timeout_secs;
    int ret;

    if (cache->last_lock_failed) {
        /* previous locking failed. don't waste time waiting on it
           again, just try once to see if it's available now. */
        nonblock = TRUE;
    }

    if (cache->index->lock_method != FILE_LOCK_METHOD_DOTLOCK) {
        i_assert(cache->file_lock == NULL);
        timeout_secs = I_MIN(MAIL_CACHE_LOCK_TIMEOUT,
                     cache->index->max_lock_timeout_secs);

        ret = mail_index_lock_fd(cache->index, cache->filepath,
                     cache->fd, F_WRLCK,
                     nonblock ? 0 : timeout_secs,
                     &cache->file_lock);
    } else {
        enum dotlock_create_flags flags =
            nonblock ? DOTLOCK_CREATE_FLAG_NONBLOCK : 0;

        i_assert(cache->dotlock == NULL);
        ret = file_dotlock_create(&cache->dotlock_settings,
                      cache->filepath, flags,
                      &cache->dotlock);
        if (ret < 0) {
            mail_cache_set_syscall_error(cache,
                             "file_dotlock_create()");
        }
    }
    cache->last_lock_failed = ret <= 0;

    /* don't bother warning if locking failed due to a timeout. since cache
       updating isn't all that important we're using a very short timeout
       so it can be triggered sometimes on heavy load */
    if (ret <= 0)
        return ret;

    mail_index_flush_read_cache(cache->index, cache->filepath, cache->fd,
                    TRUE);
    return 1;
}

static void mail_cache_unlock_file(struct mail_cache *cache)
{
    if (cache->index->lock_method != FILE_LOCK_METHOD_DOTLOCK)
        file_unlock(&cache->file_lock);
    else
        file_dotlock_delete(&cache->dotlock);
}

static int
mail_cache_lock_full(struct mail_cache *cache, bool nonblock)
{
    const struct mail_index_ext *ext;
    const void *data;
    struct mail_index_view *iview;
    uint32_t reset_id;
    int i;

    i_assert(!cache->locked);

    if (!cache->opened)
        (void)mail_cache_open_and_verify(cache);

    if (MAIL_CACHE_IS_UNUSABLE(cache) ||
        MAIL_INDEX_IS_IN_MEMORY(cache->index) ||
        cache->index->readonly)
        return 0;

    for (;;) {
        if (mail_cache_lock_file(cache, nonblock) <= 0)
            return -1;
        i_assert(!MAIL_CACHE_IS_UNUSABLE(cache));
        if (!mail_cache_need_reopen(cache)) {
            /* locked the latest file */
            break;
        }
        if (mail_cache_reopen_now(cache) <= 0) {
            i_assert(cache->file_lock == NULL);
            return -1;
        }
        i_assert(cache->file_lock == NULL);
        /* okay, so it was just compressed. try again. */
    }

    /* now verify that the index reset_id matches the cache's file_seq */
    for (i = 0; ; i++) {
        iview = mail_index_view_open(cache->index);
        ext = mail_index_view_get_ext(iview, cache->ext_id);
        reset_id = ext == NULL ? 0 : ext->reset_id;
        mail_index_view_close(&iview);

        if (cache->hdr->file_seq == reset_id)
            break;
        /* mismatch. try refreshing index once. if that doesn't help,
           we can't use the cache. */
        if (i > 0 || cache->index->mapping) {
            mail_cache_unlock_file(cache);
            return 0;
        }
        if (mail_index_refresh(cache->index) < 0) {
            mail_cache_unlock_file(cache);
            return -1;
        }
    }

    /* successfully locked - make sure our header is up to date */
    cache->locked = TRUE;
    cache->hdr_modified = FALSE;

    if (cache->file_cache != NULL) {
        file_cache_invalidate(cache->file_cache, 0,
                      sizeof(struct mail_cache_header));
    }
    if (cache->read_buf != NULL)
        buffer_set_used_size(cache->read_buf, 0);
    if (mail_cache_map(cache, 0, 0, &data) <= 0) {
        (void)mail_cache_unlock(cache);
        return -1;
    }
    cache->hdr_copy = *cache->hdr;
    return 1;
}

int mail_cache_lock(struct mail_cache *cache)
{
    return mail_cache_lock_full(cache, FALSE);
}

int mail_cache_try_lock(struct mail_cache *cache)
{
    return mail_cache_lock_full(cache, TRUE);
}

int mail_cache_unlock(struct mail_cache *cache)
{
    int ret = 0;

    i_assert(cache->locked);

    if (cache->field_header_write_pending)
                ret = mail_cache_header_fields_update(cache);

    if (MAIL_CACHE_IS_UNUSABLE(cache)) {
        /* we found it to be broken during the lock. just clean up. */
        cache->hdr_modified = FALSE;
        cache->locked = FALSE;
        return -1;
    }

    if (cache->hdr_modified) {
        cache->hdr_modified = FALSE;
        if (mail_cache_write(cache, &cache->hdr_copy,
                     sizeof(cache->hdr_copy), 0) < 0)
            ret = -1;
        cache->hdr_ro_copy = cache->hdr_copy;
        mail_cache_update_need_compress(cache);
    }

    if (cache->index->fsync_mode == FSYNC_MODE_ALWAYS) {
        if (fdatasync(cache->fd) < 0)
            mail_cache_set_syscall_error(cache, "fdatasync()");
    }

    cache->locked = FALSE;
    mail_cache_unlock_file(cache);
    return ret;
}

int mail_cache_write(struct mail_cache *cache, const void *data, size_t size,
             uoff_t offset)
{
    i_assert(cache->locked);

    if (pwrite_full(cache->fd, data, size, offset) < 0) {
        mail_cache_set_syscall_error(cache, "pwrite_full()");
        return -1;
    }

    if (cache->file_cache != NULL)
        file_cache_write(cache->file_cache, data, size, offset);
    if (cache->read_buf != NULL)
        buffer_set_used_size(cache->read_buf, 0);
    return 0;
}

int mail_cache_append(struct mail_cache *cache, const void *data, size_t size,
              uint32_t *offset)
{
    struct stat st;

    if (*offset == 0) {
        if (fstat(cache->fd, &st) < 0) {
            if (!ESTALE_FSTAT(errno))
                mail_cache_set_syscall_error(cache, "fstat()");
            return -1;
        }
        *offset = st.st_size;
    }
    if (*offset > (uint32_t)-1 || (uint32_t)-1 - *offset < size) {
        mail_cache_set_corrupted(cache, "Cache file too large");
        return -1;
    }
    if (mail_cache_write(cache, data, size, *offset) < 0)
        return -1;

    /* FIXME: this is updated only so that older Dovecot versions (<=v2.1)
       can read this file. we can remove this later. */
    cache->hdr_modified = TRUE;
    cache->hdr_copy.backwards_compat_used_file_size = *offset + size;
    return 0;
}

bool mail_cache_exists(struct mail_cache *cache)
{
    return !MAIL_CACHE_IS_UNUSABLE(cache);
}

struct mail_cache_view *
mail_cache_view_open(struct mail_cache *cache, struct mail_index_view *iview)
{
    struct mail_cache_view *view;

    view = i_new(struct mail_cache_view, 1);
    view->cache = cache;
    view->view = iview;
    view->cached_exists_buf =
        buffer_create_dynamic(default_pool,
                      cache->file_fields_count + 10);
    return view;
}

void mail_cache_view_close(struct mail_cache_view **_view)
{
    struct mail_cache_view *view = *_view;

    i_assert(view->trans_view == NULL);

    *_view = NULL;
    if (view->cache->field_header_write_pending &&
        !view->cache->compressing)
                (void)mail_cache_header_fields_update(view->cache);

    buffer_free(&view->cached_exists_buf);
    i_free(view);
}

void mail_cache_view_update_cache_decisions(struct mail_cache_view *view,
                        bool update)
{
    view->no_decision_updates = !update;
}

uint32_t mail_cache_get_first_new_seq(struct mail_index_view *view)
{
    const struct mail_index_header *idx_hdr;
    uint32_t first_new_seq, message_count;

    idx_hdr = mail_index_get_header(view);
    if (idx_hdr->day_first_uid[7] == 0)
        return 1;

    if (!mail_index_lookup_seq_range(view, idx_hdr->day_first_uid[7],
                     (uint32_t)-1, &first_new_seq,
                     &message_count)) {
        /* all messages are too old */
        return message_count+1;
    }
    return first_new_seq;
}