src/lib-index/mail-transaction-log-file.c

	mail-transaction-log-file.c revision 6f90ce01176bd920609d9d12e6419b9ba27c1359
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina/* Copyright (c) 2003-2009 Dovecot authors, see the included COPYING file */
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "lib.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "ioloop.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "buffer.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "file-dotlock.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "nfs-workarounds.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "read-full.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "write-full.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "mmap-util.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "mail-index-private.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "mail-index-modseq.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#include "mail-transaction-log-private.h"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#define LOG_PREFETCH 1024
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina#define MEMORY_LOG_NAME "(in-memory transaction log file)"
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březinavoid
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březinamail_transaction_log_file_set_corrupted(struct mail_transaction_log_file *file,
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina                    const char *fmt, ...)
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina{
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    va_list va;
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    file->corrupted = TRUE;
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    file->hdr.indexid = 0;
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina    if (!MAIL_TRANSACTION_LOG_FILE_IN_MEMORY(file)) {
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina        /* indexid=0 marks the log file as corrupted */
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina        if (pwrite_full(file->fd, &file->hdr.indexid,
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina                sizeof(file->hdr.indexid),
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina                offsetof(struct mail_transaction_log_header,
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina                     indexid)) < 0) {
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina            mail_index_file_set_syscall_error(file->log->index,
c47e9d522f0d87259e5074ea643daaa3dfcb8d92Pavel Březina                file->filepath, "pwrite()");
e5b34f0166ae61468e53f369578e691ddb09cdd0Pavel Březina        }
e5b34f0166ae61468e53f369578e691ddb09cdd0Pavel Březina    }
c47e9d522f0d87259e5074ea643daaa3dfcb8d92Pavel Březina
c47e9d522f0d87259e5074ea643daaa3dfcb8d92Pavel Březina    va_start(va, fmt);
76db25eab9010a33657f35e5afc8477c996df7a3Pavel Březina    T_BEGIN {
76db25eab9010a33657f35e5afc8477c996df7a3Pavel Březina        mail_index_set_error(file->log->index,
76db25eab9010a33657f35e5afc8477c996df7a3Pavel Březina            "Corrupted transaction log file %s seq %u: %s "
76db25eab9010a33657f35e5afc8477c996df7a3Pavel Březina            "(sync_offset=%"PRIuUOFF_T")",
76db25eab9010a33657f35e5afc8477c996df7a3Pavel Březina            file->filepath, file->hdr.file_seq,
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina            t_strdup_vprintf(fmt, va), file->sync_offset);
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    } T_END;
41ef946f3f74a46b9e26118116e4811e259b30efPavel Březina    va_end(va);
41ef946f3f74a46b9e26118116e4811e259b30efPavel Březina}
41ef946f3f74a46b9e26118116e4811e259b30efPavel Březina
41ef946f3f74a46b9e26118116e4811e259b30efPavel Březinastruct mail_transaction_log_file *
c9aab1c04c399ca2d1abef74f6df22ced34983dcPavel Březinamail_transaction_log_file_alloc(struct mail_transaction_log *log,
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina                const char *path)
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina{
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    struct mail_transaction_log_file *file;
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
41ef946f3f74a46b9e26118116e4811e259b30efPavel Březina    file = i_new(struct mail_transaction_log_file, 1);
76db25eab9010a33657f35e5afc8477c996df7a3Pavel Březina    file->log = log;
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina    file->filepath = i_strdup(path);
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina    file->fd = -1;
46d3d2c731e8c7e138462e5b60a39a279dc77d81Pavel Březina    return file;
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina}
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březinavoid mail_transaction_log_file_free(struct mail_transaction_log_file **_file)
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina{
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    struct mail_transaction_log_file *file = *_file;
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina    struct mail_transaction_log_file **p;
5ff1c3c5a12930692cb6284d14f7fda3a974af8ePavel Březina    int old_errno = errno;
20f82655b3a29cf0784ba5c912927d1ada1287dfPavel Březina
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina    *_file = NULL;
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina
5ff1c3c5a12930692cb6284d14f7fda3a974af8ePavel Březina    mail_transaction_log_file_unlock(file);
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    for (p = &file->log->files; *p != NULL; p = &(*p)->next) {
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina        if (*p == file) {
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina            *p = file->next;
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina            break;
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina        }
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    }
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    if (file == file->log->head)
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina        file->log->head = NULL;
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    if (file->buffer != NULL)
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina        buffer_free(&file->buffer);
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina    if (file->mmap_base != NULL) {
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina        if (munmap(file->mmap_base, file->mmap_size) < 0) {
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina            mail_index_file_set_syscall_error(file->log->index,
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina                              file->filepath,
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina                              "munmap()");
b0abb3bfdfd95951a23c9fc223c735805ffd2969Pavel Březina        }
c47e9d522f0d87259e5074ea643daaa3dfcb8d92Pavel Březina    }
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina    if (file->fd != -1) {
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina        if (close(file->fd) < 0) {
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina            mail_index_file_set_syscall_error(file->log->index,
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina                              file->filepath,
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina                              "close()");
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina        }
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina    }
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina
d38ffc9c92daeb62de7d28c409bdaeff98f82775Pavel Březina    i_free(file->filepath);
710472d946f6c337a095699dfd79134fa8b9eab9Pavel Březina        i_free(file);
710472d946f6c337a095699dfd79134fa8b9eab9Pavel Březina
710472d946f6c337a095699dfd79134fa8b9eab9Pavel Březina        errno = old_errno;
5ff1c3c5a12930692cb6284d14f7fda3a974af8ePavel Březina}
710472d946f6c337a095699dfd79134fa8b9eab9Pavel Březina
710472d946f6c337a095699dfd79134fa8b9eab9Pavel Březinastatic void
710472d946f6c337a095699dfd79134fa8b9eab9Pavel Březinamail_transaction_log_file_skip_to_head(struct mail_transaction_log_file *file)
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina{
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek    struct mail_transaction_log *log = file->log;
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek    struct mail_index_map *map = log->index->map;
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek    const struct mail_index_modseq_header *modseq_hdr;
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek    uoff_t head_offset;
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek
3d55c65fbe50074f6a63dcb8ae866c038a9e6b2bStephen Gallagher    if (map == NULL || file->hdr.file_seq != map->hdr.log_file_seq ||
e5b34f0166ae61468e53f369578e691ddb09cdd0Pavel Březina        map->hdr.log_file_head_offset == 0)
5ff1c3c5a12930692cb6284d14f7fda3a974af8ePavel Březina        return;
e5b34f0166ae61468e53f369578e691ddb09cdd0Pavel Březina
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek    /* we can get a valid log offset from index file. initialize
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek       sync_offset from it so we don't have to read the whole log
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek       file from beginning. */
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek    head_offset = map->hdr.log_file_head_offset;
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek    modseq_hdr = mail_index_map_get_modseq_header(map);
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek    if (head_offset < file->hdr.hdr_size) {
3b09b74bf65867d882af87ec60e2a517b15264a6Jakub Hrozek        mail_index_set_error(log->index,
2827b0d03f7b6bafa504d22a5d7ca39cbda048b3Pavel Březina                     "%s: log_file_head_offset too small",
                     log->index->filepath);
        file->sync_offset = file->hdr.hdr_size;
        file->sync_highest_modseq = file->hdr.initial_modseq;
    } else if (modseq_hdr == NULL && file->hdr.initial_modseq == 0) {
        /* modseqs not used yet */
        file->sync_offset = head_offset;
        file->sync_highest_modseq = 0;
    } else if (modseq_hdr == NULL ||
           modseq_hdr->log_seq != file->hdr.file_seq) {
        /* highest_modseq not synced, start from beginning */
        file->sync_offset = file->hdr.hdr_size;
        file->sync_highest_modseq = file->hdr.initial_modseq;
    } else if (modseq_hdr->log_offset > head_offset) {
        mail_index_set_error(log->index,
                     "%s: modseq_hdr.log_offset too large",
                     log->index->filepath);
        file->sync_offset = file->hdr.hdr_size;
        file->sync_highest_modseq = file->hdr.initial_modseq;
    } else {
        /* start from where we last stopped tracking modseqs */
        file->sync_offset = modseq_hdr->log_offset;
        file->sync_highest_modseq = modseq_hdr->highest_modseq;
    }
    if (file->hdr.file_seq == log->index->map->hdr.log_file_seq) {
        file->saved_tail_offset =
            log->index->map->hdr.log_file_tail_offset;
        file->saved_tail_sync_offset = file->saved_tail_offset;
    }
    if (file->saved_tail_offset > file->max_tail_offset)
        file->max_tail_offset = file->saved_tail_offset;
}

static void
mail_transaction_log_file_add_to_list(struct mail_transaction_log_file *file)
{
    struct mail_transaction_log_file **p;

    file->sync_offset = file->hdr.hdr_size;
    file->sync_highest_modseq = file->hdr.initial_modseq;
    mail_transaction_log_file_skip_to_head(file);

    /* insert it to correct position */
    for (p = &file->log->files; *p != NULL; p = &(*p)->next) {
        if ((*p)->hdr.file_seq > file->hdr.file_seq)
            break;
        i_assert((*p)->hdr.file_seq < file->hdr.file_seq);
    }

    file->next = *p;
    *p = file;
}

static int
mail_transaction_log_init_hdr(struct mail_transaction_log *log,
                  struct mail_transaction_log_header *hdr)
{
    struct mail_index *index = log->index;

    memset(hdr, 0, sizeof(*hdr));
    hdr->major_version = MAIL_TRANSACTION_LOG_MAJOR_VERSION;
    hdr->minor_version = MAIL_TRANSACTION_LOG_MINOR_VERSION;
    hdr->hdr_size = sizeof(struct mail_transaction_log_header);
    hdr->indexid = log->index->indexid;
    hdr->create_stamp = ioloop_time;
#ifndef WORDS_BIGENDIAN
    hdr->compat_flags |= MAIL_INDEX_COMPAT_LITTLE_ENDIAN;
#endif

    if (index->fd != -1) {
        /* not creating index - make sure we have latest header */
        if (!index->mapping) {
            if (mail_index_map(index,
                       MAIL_INDEX_SYNC_HANDLER_HEAD) <= 0)
                return -1;
        } else {
            /* if we got here from mapping, the .log file is
               corrupted. use whatever values we got from index
               file */
        }
    }
    if (index->map != NULL) {
        hdr->prev_file_seq = index->map->hdr.log_file_seq;
        hdr->prev_file_offset = index->map->hdr.log_file_head_offset;
        hdr->file_seq = index->map->hdr.log_file_seq + 1;
        hdr->initial_modseq =
            mail_index_map_modseq_get_highest(index->map);
    } else {
        hdr->file_seq = 1;
    }

    if (log->head != NULL) {
        if (hdr->file_seq <= log->head->hdr.file_seq) {
            /* make sure the sequence grows */
            hdr->file_seq = log->head->hdr.file_seq+1;
        }
        if (hdr->initial_modseq < log->head->sync_highest_modseq) {
            /* this should be always up-to-date */
            hdr->initial_modseq = log->head->sync_highest_modseq;
        }
    }
    return 0;
}

struct mail_transaction_log_file *
mail_transaction_log_file_alloc_in_memory(struct mail_transaction_log *log)
{
    struct mail_transaction_log_file *file;

    file = mail_transaction_log_file_alloc(log, MEMORY_LOG_NAME);
    if (mail_transaction_log_init_hdr(log, &file->hdr) < 0) {
        i_free(file);
        return NULL;
    }

    file->buffer = buffer_create_dynamic(default_pool, 4096);
    file->buffer_offset = sizeof(file->hdr);

    mail_transaction_log_file_add_to_list(file);
    return file;
}

static int
mail_transaction_log_file_dotlock(struct mail_transaction_log_file *file)
{
    int ret;

    if (file->log->dotlock_count > 0)
        ret = 1;
    else {
        ret = file_dotlock_create(&file->log->dotlock_settings,
                      file->filepath, 0,
                      &file->log->dotlock);
    }
    if (ret > 0) {
        file->log->dotlock_count++;
        file->locked = TRUE;
        return 0;
    }
    if (ret < 0) {
        mail_index_file_set_syscall_error(file->log->index,
                          file->filepath,
                          "file_dotlock_create()");
        return -1;
    }

    mail_index_set_error(file->log->index,
                 "Timeout while waiting for "
                 "dotlock for transaction log file %s",
                 file->filepath);
    file->log->index->index_lock_timeout = TRUE;
    return -1;
}

static int
mail_transaction_log_file_undotlock(struct mail_transaction_log_file *file)
{
    int ret;

    if (--file->log->dotlock_count > 0)
        return 0;

    ret = file_dotlock_delete(&file->log->dotlock);
    if (ret < 0) {
        mail_index_file_set_syscall_error(file->log->index,
            file->filepath, "file_dotlock_delete()");
        return -1;
    }

    if (ret == 0) {
        mail_index_set_error(file->log->index,
            "Dotlock was lost for transaction log file %s",
            file->filepath);
        return -1;
    }
    return 0;
}

int mail_transaction_log_file_lock(struct mail_transaction_log_file *file)
{
    int ret;

    if (file->locked)
        return 0;

    if (MAIL_TRANSACTION_LOG_FILE_IN_MEMORY(file)) {
        file->locked = TRUE;
        return 0;
    }

    if (file->log->index->lock_method == FILE_LOCK_METHOD_DOTLOCK)
        return mail_transaction_log_file_dotlock(file);

    i_assert(file->file_lock == NULL);
    ret = mail_index_lock_fd(file->log->index, file->filepath, file->fd,
                 F_WRLCK, MAIL_TRANSCATION_LOG_LOCK_TIMEOUT,
                 &file->file_lock);
    if (ret > 0) {
        file->locked = TRUE;
        return 0;
    }
    if (ret < 0) {
        mail_index_file_set_syscall_error(file->log->index,
                          file->filepath,
                          "mail_index_wait_lock_fd()");
        return -1;
    }

    mail_index_set_error(file->log->index,
        "Timeout while waiting for lock for transaction log file %s",
        file->filepath);
    file->log->index->index_lock_timeout = TRUE;
    return -1;
}

void mail_transaction_log_file_unlock(struct mail_transaction_log_file *file)
{
    if (!file->locked)
        return;

    file->locked = FALSE;

    if (MAIL_TRANSACTION_LOG_FILE_IN_MEMORY(file))
        return;

    if (file->log->index->lock_method == FILE_LOCK_METHOD_DOTLOCK) {
        mail_transaction_log_file_undotlock(file);
        return;
    }

    file_unlock(&file->file_lock);
}

static ssize_t
mail_transaction_log_file_read_header(struct mail_transaction_log_file *file)
{
    ssize_t pos;
    int ret;

    memset(&file->hdr, 0, sizeof(file->hdr));

        /* try to read the whole header, but it's not necessarily an error to
       read less since the older versions of the log format could be
       smaller. */
        pos = 0;
    do {
        ret = pread(file->fd, PTR_OFFSET(&file->hdr, pos),
                sizeof(file->hdr) - pos, pos);
        if (ret > 0)
            pos += ret;
    } while (ret > 0 && pos < (ssize_t)sizeof(file->hdr));
    return ret < 0 ? -1 : pos;
}

static int
mail_transaction_log_file_read_hdr(struct mail_transaction_log_file *file,
                   bool ignore_estale)
{
        struct mail_transaction_log_file *f;
    int ret;

    i_assert(!MAIL_TRANSACTION_LOG_FILE_IN_MEMORY(file));

    if (file->corrupted)
        return 0;

    ret = mail_transaction_log_file_read_header(file);
    if (ret < 0) {
                if (errno != ESTALE || !ignore_estale) {
                        mail_index_file_set_syscall_error(file->log->index,
                                                          file->filepath,
                                                          "pread()");
                }
        return -1;
    }
    if (file->hdr.major_version != MAIL_TRANSACTION_LOG_MAJOR_VERSION) {
        /* incompatible version - fix silently */
        return 0;
    }
    if (ret < MAIL_TRANSACTION_LOG_HEADER_MIN_SIZE) {
        mail_transaction_log_file_set_corrupted(file,
            "unexpected end of file while reading header");
        return 0;
    }

    if (file->hdr.minor_version >= 2 || file->hdr.major_version > 1) {
        /* we have compatibility flags */
        enum mail_index_header_compat_flags compat_flags = 0;

#ifndef WORDS_BIGENDIAN
        compat_flags |= MAIL_INDEX_COMPAT_LITTLE_ENDIAN;
#endif
        if (file->hdr.compat_flags != compat_flags) {
            /* architecture change */
            mail_index_set_error(file->log->index,
                         "Rebuilding index file %s: "
                         "CPU architecture changed",
                         file->log->index->filepath);
            return 0;
        }
    }
    if (file->hdr.hdr_size < MAIL_TRANSACTION_LOG_HEADER_MIN_SIZE) {
        mail_transaction_log_file_set_corrupted(file,
            "Header size too small");
        return 0;
    }
    if (file->hdr.hdr_size < sizeof(file->hdr)) {
        /* @UNSAFE: smaller than we expected - zero out the fields we
           shouldn't have filled */
        memset(PTR_OFFSET(&file->hdr, file->hdr.hdr_size), 0,
               sizeof(file->hdr) - file->hdr.hdr_size);
    }

    if (file->hdr.indexid == 0) {
        /* corrupted */
        file->corrupted = TRUE;
        mail_index_set_error(file->log->index,
            "Transaction log file %s: marked corrupted",
            file->filepath);
        return 0;
    }
    if (file->hdr.indexid != file->log->index->indexid) {
        if (file->log->index->indexid != 0 &&
            !file->log->index->initial_create) {
            /* index file was probably just rebuilt and we don't
               know about it yet */
            mail_transaction_log_file_set_corrupted(file,
                "indexid changed %u -> %u",
                file->log->index->indexid, file->hdr.indexid);
            return 0;
        }

        /* creating index file. since transaction log is created
           first, use the indexid in it to create the main index
           to avoid races. */
        file->log->index->indexid = file->hdr.indexid;
    }

    /* make sure we already don't have a file with the same sequence
       opened. it shouldn't happen unless the old log file was
       corrupted. */
    for (f = file->log->files; f != NULL; f = f->next) {
        if (f->hdr.file_seq == file->hdr.file_seq) {
            /* mark the old file corrupted. we can't safely remove
               it from the list however, so return failure. */
            mail_transaction_log_file_set_corrupted(f,
                "duplicate transaction log sequence (%u)",
                f->hdr.file_seq);
            return 0;
        }
    }

    file->sync_highest_modseq = file->hdr.initial_modseq;
    return 1;
}

static int
mail_transaction_log_file_stat(struct mail_transaction_log_file *file,
                   bool ignore_estale)
{
    struct stat st;

    if (fstat(file->fd, &st) < 0) {
                if (errno != ESTALE || !ignore_estale) {
            mail_index_file_set_syscall_error(file->log->index,
                file->filepath, "fstat()");
                }
        return -1;
    }

    file->st_dev = st.st_dev;
    file->st_ino = st.st_ino;
    file->last_mtime = st.st_mtime;
    file->last_size = st.st_size;
    return 0;
}

static bool
mail_transaction_log_file_is_dupe(struct mail_transaction_log_file *file)
{
    struct mail_transaction_log_file *tmp;

    for (tmp = file->log->files; tmp != NULL; tmp = tmp->next) {
        if (tmp->st_ino == file->st_ino &&
            CMP_DEV_T(tmp->st_dev, file->st_dev))
            return TRUE;
    }
    return FALSE;
}

static int
mail_transaction_log_file_create2(struct mail_transaction_log_file *file,
                  int new_fd, bool reset,
                  struct dotlock **dotlock)
{
    struct mail_index *index = file->log->index;
    struct stat st;
    const char *path2;
    int fd, ret;
    bool rename_existing;

    if (index->nfs_flush) {
        /* although we check also mtime and file size below, it's done
           only to fix broken log files. we don't bother flushing
           attribute cache just for that. */
        nfs_flush_file_handle_cache(file->filepath);
    }

    /* log creation is locked now - see if someone already created it.
       note that if we're rotating, we need to keep the log locked until
       the file has been rewritten. and because fcntl() locks are stupid,
       if we go and open()+close() the file and we had it already opened,
       its locks are lost. so we use stat() to check if the file has been
       recreated, although it almost never is. */
    if (reset)
        rename_existing = FALSE;
    else if (nfs_safe_stat(file->filepath, &st) < 0) {
        if (errno != ENOENT) {
            mail_index_file_set_syscall_error(index, file->filepath,
                              "stat()");
            return -1;
        }
        rename_existing = FALSE;
    } else if (st.st_ino == file->st_ino &&
           CMP_DEV_T(st.st_dev, file->st_dev) &&
           /* inode/dev checks are enough when we're rotating the file,
              but not when we're replacing a broken log file */
           st.st_mtime == file->last_mtime &&
           (uoff_t)st.st_size == file->last_size) {
        /* no-one else recreated the file */
        rename_existing = TRUE;
    } else {
        /* recreated. use the file if its header is ok */
        fd = nfs_safe_open(file->filepath, O_RDWR);
        if (fd == -1) {
            if (errno != ENOENT) {
                mail_index_file_set_syscall_error(index,
                    file->filepath, "open()");
                return -1;
            }
        } else {
            file->fd = fd;
            if (mail_transaction_log_file_read_hdr(file,
                                   FALSE) > 0 &&
                mail_transaction_log_file_stat(file, FALSE) == 0) {
                /* yes, it was ok */
                (void)file_dotlock_delete(dotlock);
                mail_transaction_log_file_add_to_list(file);
                return 0;
            }
            file->fd = -1;
            if (close(fd) < 0) {
                mail_index_file_set_syscall_error(index,
                    file->filepath, "close()");
            }
        }
        rename_existing = FALSE;
    }

    if (mail_transaction_log_init_hdr(file->log, &file->hdr) < 0)
        return -1;

    if (reset) {
        /* don't reset modseqs. if we're reseting due to rebuilding
           indexes we'll probably want to keep uidvalidity and in such
           cases we really don't want to shrink modseqs. */
        file->hdr.prev_file_seq = 0;
        file->hdr.prev_file_offset = 0;
    }

    if (write_full(new_fd, &file->hdr, sizeof(file->hdr)) < 0) {
        mail_index_file_set_syscall_error(index, file->filepath,
                          "write_full()");
        return -1;
    }

    if (index->nfs_flush) {
        /* the header isn't important, so don't bother calling
           fdatasync() unless NFS is used */
        if (fdatasync(new_fd) < 0) {
            mail_index_file_set_syscall_error(index, file->filepath,
                              "fdatasync()");
            return -1;
        }
    }

    file->fd = new_fd;
    ret = mail_transaction_log_file_stat(file, FALSE);

    if (file->log->head != NULL && file->log->head->locked) {
        /* we'll need to preserve the lock */
        if (mail_transaction_log_file_lock(file) < 0)
            ret = -1;
    }

    /* if we return -1 the dotlock deletion code closes the fd */
    file->fd = -1;
    if (ret < 0)
        return -1;

    /* keep two log files */
    if (rename_existing) {
        /* rename() would be nice and easy way to do this, except then
           there's a race condition between the rename and
           file_dotlock_replace(). during that time the log file
           doesn't exist, which could cause problems. */
        path2 = t_strconcat(file->filepath, ".2", NULL);
        if (unlink(path2) < 0 && errno != ENOENT) {
                        mail_index_set_error(index, "unlink(%s) failed: %m",
                         path2);
            /* try to link() anyway */
        }
        if (nfs_safe_link(file->filepath, path2, FALSE) < 0 &&
            errno != ENOENT && errno != EEXIST) {
                        mail_index_set_error(index, "link(%s, %s) failed: %m",
                         file->filepath, path2);
            /* ignore the error. we don't care that much about the
               second log file and we're going to overwrite this
               first one. */
        }
    }

    if (file_dotlock_replace(dotlock,
                 DOTLOCK_REPLACE_FLAG_DONT_CLOSE_FD) <= 0)
        return -1;

    /* success */
    file->fd = new_fd;
        mail_transaction_log_file_add_to_list(file);
    return 0;
}

int mail_transaction_log_file_create(struct mail_transaction_log_file *file,
                     bool reset)
{
    struct mail_index *index = file->log->index;
    struct dotlock *dotlock;
    mode_t old_mask;
    int fd;

    i_assert(!MAIL_INDEX_IS_IN_MEMORY(index));

    /* With dotlocking we might already have path.lock created, so this
       filename has to be different. */
    old_mask = umask(index->mode ^ 0666);
    fd = file_dotlock_open(&file->log->new_dotlock_settings,
                   file->filepath, 0, &dotlock);
    umask(old_mask);

    if (fd == -1) {
        mail_index_file_set_syscall_error(index, file->filepath,
                          "file_dotlock_open()");
        return -1;
    }

    if (index->gid != (gid_t)-1 &&
        fchown(fd, (uid_t)-1, index->gid) < 0) {
        mail_index_file_set_syscall_error(index, file->filepath,
                          "fchown()");
        (void)file_dotlock_delete(&dotlock);
        return -1;
    }

        /* either fd gets used or the dotlock gets deleted and returned fd
           is for the existing file */
        if (mail_transaction_log_file_create2(file, fd, reset, &dotlock) < 0) {
        if (dotlock != NULL)
            (void)file_dotlock_delete(&dotlock);
        return -1;
    }
    return 0;
}

int mail_transaction_log_file_open(struct mail_transaction_log_file *file,
                   bool check_existing)
{
        unsigned int i;
    bool ignore_estale;
    int ret;

        for (i = 0;; i++) {
                file->fd = nfs_safe_open(file->filepath, O_RDWR);
                if (file->fd == -1) {
            if (errno == ENOENT)
                return 0;

            mail_index_file_set_syscall_error(file->log->index,
                file->filepath, "open()");
            return -1;
                }

        ignore_estale = i < MAIL_INDEX_ESTALE_RETRY_COUNT;
        if (mail_transaction_log_file_stat(file, ignore_estale) < 0)
            ret = -1;
        else if (check_existing &&
             mail_transaction_log_file_is_dupe(file))
            return 0;
        else {
            ret = mail_transaction_log_file_read_hdr(file,
                                 ignore_estale);
        }
        if (ret > 0) {
            /* success */
            break;
        }

        if (ret == 0) {
            /* corrupted */
            if (unlink(file->filepath) < 0 && errno != ENOENT) {
                mail_index_set_error(file->log->index,
                             "unlink(%s) failed: %m",
                             file->filepath);
            }
            return 0;
        }
        if (errno != ESTALE ||
            i == MAIL_INDEX_ESTALE_RETRY_COUNT) {
            /* syscall error */
            return -1;
        }

        /* ESTALE - try again */
        }

    mail_transaction_log_file_add_to_list(file);
    return 1;
}

static int
log_file_track_mailbox_sync_offset_hdr(struct mail_transaction_log_file *file,
                       const void *data, unsigned int size)
{
    const struct mail_transaction_header_update *u = data;
    const struct mail_index_header *ihdr;
    const unsigned int offset_pos =
        offsetof(struct mail_index_header, log_file_tail_offset);
    const unsigned int offset_size = sizeof(ihdr->log_file_tail_offset);
    uint32_t tail_offset;

    i_assert(offset_size == sizeof(tail_offset));

    if (size < sizeof(*u) || size < sizeof(*u) + u->size) {
        mail_transaction_log_file_set_corrupted(file,
            "header update extends beyond record size");
        return -1;
    }

    if (u->offset <= offset_pos &&
        u->offset + u->size >= offset_pos + offset_size) {
        memcpy(&tail_offset,
               CONST_PTR_OFFSET(u + 1, offset_pos - u->offset),
               sizeof(tail_offset));

        if (tail_offset < file->saved_tail_offset) {
            if (file->sync_offset < file->saved_tail_sync_offset) {
                /* saved_tail_offset was already set in header,
                   but we still had to resync the file to find
                   modseqs. ignore this record. */
                return 1;
            }
            mail_index_set_error(file->log->index,
                "Transaction log file %s seq %u: "
                "log_file_tail_offset update shrank it "
                "(%u vs %"PRIuUOFF_T" "
                "sync_offset=%"PRIuUOFF_T")",
                file->filepath, file->hdr.file_seq,
                tail_offset, file->saved_tail_offset,
                file->sync_offset);
        } else {
            file->saved_tail_offset = tail_offset;
            if (tail_offset > file->max_tail_offset)
                file->max_tail_offset = tail_offset;
            return 1;
        }
    }
    return 0;
}

bool
mail_transaction_header_has_modseq(const struct mail_transaction_header *hdr,
                   const void *data,
                   uint64_t cur_modseq)
{
    if (cur_modseq != 0) {
        /* tracking modseqs */
    } else if ((hdr->type & MAIL_TRANSACTION_TYPE_MASK) ==
           MAIL_TRANSACTION_EXT_INTRO) {
        /* modseqs not tracked yet. see if this is a modseq
           extension introduction. */
        const struct mail_transaction_ext_intro *intro = data;
        const unsigned int modseq_ext_len =
            strlen(MAIL_INDEX_MODSEQ_EXT_NAME);

        if (intro->name_size == modseq_ext_len &&
            memcmp(intro + 1, MAIL_INDEX_MODSEQ_EXT_NAME,
               modseq_ext_len) == 0) {
            /* modseq tracking started */
            return TRUE;
        }
    } else {
        /* not tracking modseqs */
        return FALSE;
    }

    switch (hdr->type & MAIL_TRANSACTION_TYPE_MASK) {
    case MAIL_TRANSACTION_EXPUNGE | MAIL_TRANSACTION_EXPUNGE_PROT:
        if ((hdr->type & MAIL_TRANSACTION_EXTERNAL) == 0) {
            /* ignore expunge requests */
            break;
        }
    case MAIL_TRANSACTION_APPEND:
    case MAIL_TRANSACTION_FLAG_UPDATE:
    case MAIL_TRANSACTION_KEYWORD_UPDATE:
    case MAIL_TRANSACTION_KEYWORD_RESET:
        /* these changes increase modseq */
        return TRUE;
    }
    return FALSE;
}

static struct modseq_cache *
modseq_cache_hit(struct mail_transaction_log_file *file, unsigned int idx)
{
    struct modseq_cache cache;

    if (idx > 0) {
        /* @UNSAFE: move it to top */
        cache = file->modseq_cache[idx];
        memmove(file->modseq_cache + 1, file->modseq_cache,
            sizeof(*file->modseq_cache) * idx);
        file->modseq_cache[0] = cache;
    }
    return &file->modseq_cache[0];
}

static struct modseq_cache *
modseq_cache_get_offset(struct mail_transaction_log_file *file, uoff_t offset)
{
    unsigned int i, best = -1U;

    for (i = 0; i < N_ELEMENTS(file->modseq_cache); i++) {
        if (offset < file->modseq_cache[i].offset)
            continue;

        if (file->modseq_cache[i].offset == 0)
            return NULL;

        if (offset == file->modseq_cache[i].offset) {
            /* exact cache hit */
            return modseq_cache_hit(file, i);
        }

        if (best == -1U ||
            file->modseq_cache[i].offset <
            file->modseq_cache[best].offset)
            best = i;
    }
    if (best == -1U)
        return NULL;
    return &file->modseq_cache[best];
}

static struct modseq_cache *
modseq_cache_get_modseq(struct mail_transaction_log_file *file, uint64_t modseq)
{
    unsigned int i, best = -1U;

    for (i = 0; i < N_ELEMENTS(file->modseq_cache); i++) {
        if (modseq < file->modseq_cache[i].highest_modseq)
            continue;

        if (file->modseq_cache[i].offset == 0)
            return NULL;

        if (modseq == file->modseq_cache[i].highest_modseq) {
            /* exact cache hit */
            return modseq_cache_hit(file, i);
        }

        if (best == -1U ||
            file->modseq_cache[i].highest_modseq <
            file->modseq_cache[best].highest_modseq)
            best = i;
    }
    if (best == -1U)
        return NULL;
    return &file->modseq_cache[best];
}

static int
log_get_synced_record(struct mail_transaction_log_file *file, uoff_t *offset,
              const struct mail_transaction_header **hdr_r)
{
    const struct mail_transaction_header *hdr;
    uint32_t trans_size;

    hdr = CONST_PTR_OFFSET(file->buffer->data,
                   *offset - file->buffer_offset);

    /* we've already synced this record at some point. it should
       be valid. */
    trans_size = mail_index_offset_to_uint32(hdr->size);
    if (trans_size < sizeof(*hdr) ||
        *offset - file->buffer_offset + trans_size > file->buffer->used) {
        mail_transaction_log_file_set_corrupted(file,
            "Transaction log corrupted unexpectedly at "
            "%"PRIuUOFF_T": Invalid size %u (type=%x)",
            *offset, trans_size, hdr->type);
        return -1;
    }
    *offset += trans_size;
    *hdr_r = hdr;
    return 0;
}

int mail_transaction_log_file_get_highest_modseq_at(
        struct mail_transaction_log_file *file,
        uoff_t offset, uint64_t *highest_modseq_r)
{
    const struct mail_transaction_header *hdr;
    struct modseq_cache *cache;
    uoff_t cur_offset;
    uint64_t cur_modseq;
    int ret;

    i_assert(offset <= file->sync_offset);

    if (offset == file->sync_offset) {
        *highest_modseq_r = file->sync_highest_modseq;
        return 0;
    }

    cache = modseq_cache_get_offset(file, offset);
    if (cache == NULL) {
        /* nothing usable in cache - scan from beginning */
        cur_offset = file->hdr.hdr_size;
        cur_modseq = file->hdr.initial_modseq;
    } else if (cache->offset == offset) {
        /* exact cache hit */
        *highest_modseq_r = cache->highest_modseq;
        return 0;
    } else {
        /* use cache to skip over some records */
        cur_offset = cache->offset;
        cur_modseq = cache->highest_modseq;
    }

    ret = mail_transaction_log_file_map(file, cur_offset, offset);
    if (ret <= 0) {
        if (ret < 0)
            return -1;
        mail_index_set_error(file->log->index,
            "%s: Transaction log corrupted, can't get modseq",
            file->filepath);
        return -1;
    }

    i_assert(cur_offset >= file->buffer_offset);
    i_assert(cur_offset + file->buffer->used >= offset);
    while (cur_offset < offset) {
        if (log_get_synced_record(file, &cur_offset, &hdr) < 0)
            return- 1;
        if (mail_transaction_header_has_modseq(hdr, hdr + 1,
                               cur_modseq))
            cur_modseq++;
    }

    /* @UNSAFE: cache the value */
    memmove(file->modseq_cache + 1, file->modseq_cache,
        sizeof(*file->modseq_cache) *
        (N_ELEMENTS(file->modseq_cache) - 1));
    file->modseq_cache[0].offset = cur_offset;
    file->modseq_cache[0].highest_modseq = cur_modseq;

    *highest_modseq_r = cur_modseq;
    return 0;
}

int mail_transaction_log_file_get_modseq_next_offset(
        struct mail_transaction_log_file *file,
        uint64_t modseq, uoff_t *next_offset_r)
{
    const struct mail_transaction_header *hdr;
    struct modseq_cache *cache;
    uoff_t cur_offset, prev_offset;
    uint64_t cur_modseq;
    int ret;

    if (modseq >= file->sync_highest_modseq) {
        *next_offset_r = file->sync_offset;
        return 0;
    }

    cache = modseq_cache_get_modseq(file, modseq);
    if (cache == NULL) {
        /* nothing usable in cache - scan from beginning */
        cur_offset = file->hdr.hdr_size;
        cur_modseq = file->hdr.initial_modseq;
    } else if (cache->highest_modseq == modseq) {
        /* exact cache hit */
        *next_offset_r = cache->offset;
        return 0;
    } else {
        /* use cache to skip over some records */
        cur_offset = cache->offset;
        cur_modseq = cache->highest_modseq;
    }

    ret = mail_transaction_log_file_map(file, cur_offset,
                        file->sync_offset);
    if (ret <= 0) {
        if (ret < 0)
            return -1;
        mail_index_set_error(file->log->index,
            "%s: Transaction log corrupted, can't get modseq",
            file->filepath);
        return -1;
    }

    i_assert(cur_offset >= file->buffer_offset);
    while (cur_offset < file->sync_offset) {
        prev_offset = cur_offset;
        if (log_get_synced_record(file, &cur_offset, &hdr) < 0)
            return -1;
        if (mail_transaction_header_has_modseq(hdr, hdr + 1,
                               cur_modseq)) {
            if (++cur_modseq == modseq)
                break;
        }
    }
    if (modseq != cur_modseq) {
        /* if we got to sync_offset, cur_modseq should be
           sync_highest_modseq */
        mail_index_set_error(file->log->index,
            "%s: Transaction log changed unexpectedly, "
            "can't get modseq", file->filepath);
        return -1;
    }

    /* @UNSAFE: cache the value */
    memmove(file->modseq_cache + 1, file->modseq_cache,
        sizeof(*file->modseq_cache) *
        (N_ELEMENTS(file->modseq_cache) - 1));
    file->modseq_cache[0].offset = cur_offset;
    file->modseq_cache[0].highest_modseq = cur_modseq;

    *next_offset_r = cur_offset;
    return 0;
}

static int
log_file_track_sync(struct mail_transaction_log_file *file,
            const struct mail_transaction_header *hdr,
            unsigned int trans_size)
{
    const void *data = hdr + 1;
    int ret;

    if (mail_transaction_header_has_modseq(hdr, hdr + 1,
                           file->sync_highest_modseq))
        file->sync_highest_modseq++;
    if ((hdr->type & MAIL_TRANSACTION_EXTERNAL) == 0)
        return 0;

    /* external transactions: */
    if ((hdr->type & MAIL_TRANSACTION_TYPE_MASK) ==
        MAIL_TRANSACTION_HEADER_UPDATE) {
        /* see if this updates mailbox_sync_offset */
        ret = log_file_track_mailbox_sync_offset_hdr(file, data,
                                 trans_size -
                                 sizeof(*hdr));
        if (ret != 0)
            return ret < 0 ? -1 : 0;
    }

    if (file->max_tail_offset == file->sync_offset) {
        /* external transactions aren't synced to mailbox. we can
           update mailbox sync offset to skip this transaction to
           avoid re-reading it at the next sync. */
        file->max_tail_offset += trans_size;
    }
    return 0;
}

static int
mail_transaction_log_file_sync(struct mail_transaction_log_file *file)
{
        const struct mail_transaction_header *hdr;
    const void *data;
    struct stat st;
    size_t size, avail;
    uint32_t trans_size = 0;

    i_assert(file->sync_offset >= file->buffer_offset);

    data = buffer_get_data(file->buffer, &size);
    while (file->sync_offset - file->buffer_offset + sizeof(*hdr) <= size) {
        hdr = CONST_PTR_OFFSET(data, file->sync_offset -
                       file->buffer_offset);
        trans_size = mail_index_offset_to_uint32(hdr->size);
        if (trans_size == 0) {
            /* unfinished */
            return 1;
        }
        if (trans_size < sizeof(*hdr)) {
            mail_transaction_log_file_set_corrupted(file,
                "hdr.size too small (%u)", trans_size);
            return -1;
        }

        if (file->sync_offset - file->buffer_offset + trans_size > size)
            break;

        /* transaction has been fully written */
        if (log_file_track_sync(file, hdr, trans_size) < 0)
            return -1;

        file->sync_offset += trans_size;
        trans_size = 0;
    }

    if (file->mmap_base != NULL && !file->locked) {
        /* Now that all the mmaped pages have page faulted, check if
           the file had changed while doing that. Only after the last
           page has faulted, the size returned by fstat() can be
           trusted. Otherwise it might point to a page boundary while
           the next page is still being written.

           Without this check we might see partial transactions,
           sometimes causing "Extension record updated without intro
           prefix" errors. */
        if (fstat(file->fd, &st) < 0) {
            mail_index_file_set_syscall_error(file->log->index,
                              file->filepath,
                              "fstat()");
            return -1;
        }
        if ((uoff_t)st.st_size != file->last_size) {
            file->last_size = st.st_size;
            return 0;
        }
    }

    avail = file->sync_offset - file->buffer_offset;
    if (avail != size) {
        /* There's more data than we could sync at the moment. If the
           last record's size wasn't valid, we can't know if it will
           be updated unless we've locked the log. */
        if (trans_size != 0) {
            /* pread()s or the above fstat() check for mmaps should
               have guaranteed that this doesn't happen */
            mail_transaction_log_file_set_corrupted(file,
                "hdr.size too large (%u)", trans_size);
            return -1;
        } else if (file->locked) {
            mail_transaction_log_file_set_corrupted(file,
                "Unexpected garbage at EOF");
            return -1;
        }

        /* The size field will be updated soon */
        mail_index_flush_read_cache(file->log->index, file->filepath,
                        file->fd, file->locked);
    }

    if (file->next != NULL &&
        file->hdr.file_seq == file->next->hdr.prev_file_seq &&
        file->next->hdr.prev_file_offset != file->sync_offset) {
        mail_transaction_log_file_set_corrupted(file,
            "Invalid transaction log size "
            "(%"PRIuUOFF_T" vs %u): %s", file->sync_offset,
            file->log->head->hdr.prev_file_offset, file->filepath);
        return -1;
    }

    return 1;
}

static int
mail_transaction_log_file_insert_read(struct mail_transaction_log_file *file,
                      uoff_t offset)
{
    void *data;
    size_t size;
    ssize_t ret;

    size = file->buffer_offset - offset;
    buffer_copy(file->buffer, size, file->buffer, 0, (size_t)-1);

    data = buffer_get_space_unsafe(file->buffer, 0, size);
    ret = pread_full(file->fd, data, size, offset);
    if (ret > 0) {
        /* success */
        file->buffer_offset -= size;
        return 1;
    }

    /* failure. don't leave ourself to inconsistent state */
    buffer_copy(file->buffer, 0, file->buffer, size, (size_t)-1);
    buffer_set_used_size(file->buffer, file->buffer->used - size);

    if (ret == 0) {
        mail_transaction_log_file_set_corrupted(file, "file shrank");
        return 0;
    } else if (errno == ESTALE) {
        /* log file was deleted in NFS server, fail silently */
        return 0;
    } else {
        mail_index_file_set_syscall_error(file->log->index,
                          file->filepath, "pread()");
        return -1;
    }
}

static int
mail_transaction_log_file_read_more(struct mail_transaction_log_file *file)
{
    void *data;
    size_t size;
    uint32_t read_offset;
    ssize_t ret;

    read_offset = file->buffer_offset + buffer_get_used_size(file->buffer);

    do {
        data = buffer_append_space_unsafe(file->buffer, LOG_PREFETCH);
        ret = pread(file->fd, data, LOG_PREFETCH, read_offset);
        if (ret > 0)
            read_offset += ret;

        size = read_offset - file->buffer_offset;
        buffer_set_used_size(file->buffer, size);
    } while (ret > 0 || (ret < 0 && errno == EINTR));

    file->last_size = read_offset;

    if (ret < 0) {
        if (errno == ESTALE) {
            /* log file was deleted in NFS server, fail silently */
            return 0;
        }

        mail_index_file_set_syscall_error(file->log->index,
                          file->filepath, "pread()");
        return -1;
    }
    return 1;
}

static bool
mail_transaction_log_file_need_nfs_flush(struct mail_transaction_log_file *file)
{
    const struct mail_index_header *hdr = &file->log->index->map->hdr;
    uoff_t max_offset = file->last_size;

    if (file->next != NULL &&
        file->hdr.file_seq == file->next->hdr.prev_file_seq &&
        file->next->hdr.prev_file_offset != max_offset) {
        /* we already have a newer log file which says that we haven't
           synced the entire file. */
        return TRUE;
    }

    if (file->hdr.file_seq == hdr->log_file_seq &&
        max_offset < hdr->log_file_head_offset)
        return TRUE;

    return FALSE;
}

static int
mail_transaction_log_file_read(struct mail_transaction_log_file *file,
                   uoff_t start_offset, bool nfs_flush)
{
    int ret;

    i_assert(file->mmap_base == NULL);

    /* NFS: if file isn't locked, we're optimistic that we can read enough
       data without flushing attribute cache. if after reading we notice
       that we really should have read more, flush the cache and try again.
       if file is locked, the attribute cache was already flushed when
       refreshing the log. */
    if (file->log->index->nfs_flush && nfs_flush) {
        if (!file->locked)
            nfs_flush_attr_cache_unlocked(file->filepath);
        else {
            nfs_flush_attr_cache_fd_locked(file->filepath,
                               file->fd);
        }
    }

    if (file->buffer != NULL && file->buffer_offset > start_offset) {
        /* we have to insert missing data to beginning of buffer */
        ret = mail_transaction_log_file_insert_read(file, start_offset);
        if (ret <= 0)
            return ret;
    }

    if (file->buffer == NULL) {
        file->buffer =
            buffer_create_dynamic(default_pool, LOG_PREFETCH);
        file->buffer_offset = start_offset;
    }

    if ((ret = mail_transaction_log_file_read_more(file)) <= 0)
        return ret;

    if (file->log->index->nfs_flush && !nfs_flush &&
        mail_transaction_log_file_need_nfs_flush(file)) {
        /* we didn't read enough data. flush and try again. */
        return mail_transaction_log_file_read(file, start_offset, TRUE);
    }

    if ((ret = mail_transaction_log_file_sync(file)) <= 0) {
        i_assert(ret != 0); /* happens only with mmap */
        return -1;
    }

    i_assert(file->sync_offset >= file->buffer_offset);
    buffer_set_used_size(file->buffer,
                 file->sync_offset - file->buffer_offset);
    return 1;
}

static int
log_file_map_check_offsets(struct mail_transaction_log_file *file,
               uoff_t start_offset, uoff_t end_offset)
{
    if (start_offset > file->sync_offset) {
        /* broken start offset */
        mail_index_set_error(file->log->index,
            "%s: start_offset (%"PRIuUOFF_T") > "
            "current sync_offset (%"PRIuUOFF_T")",
            file->filepath, start_offset, file->sync_offset);
        return 0;
    }
    if (end_offset != (uoff_t)-1 && end_offset > file->sync_offset) {
        mail_index_set_error(file->log->index,
            "%s: end_offset (%"PRIuUOFF_T") > "
            "current sync_offset (%"PRIuUOFF_T")",
            file->filepath, start_offset, file->sync_offset);
        return 0;
    }

    return 1;
}

static int
mail_transaction_log_file_mmap(struct mail_transaction_log_file *file)
{
    if (file->buffer != NULL) {
        /* in case we just switched to mmaping */
        buffer_free(&file->buffer);
    }
    file->mmap_size = file->last_size;
    file->mmap_base = mmap(NULL, file->mmap_size, PROT_READ, MAP_SHARED,
                   file->fd, 0);
    if (file->mmap_base == MAP_FAILED) {
        file->mmap_base = NULL;
        file->mmap_size = 0;
        mail_index_file_set_syscall_error(file->log->index,
                          file->filepath, "mmap()");
        return -1;
    }

    if (file->mmap_size > mmap_get_page_size()) {
        if (madvise(file->mmap_base, file->mmap_size,
                MADV_SEQUENTIAL) < 0) {
            mail_index_file_set_syscall_error(file->log->index,
                file->filepath, "madvise()");
        }
    }

    file->buffer = buffer_create_const_data(default_pool,
                        file->mmap_base,
                        file->mmap_size);
    file->buffer_offset = 0;
    return 0;
}

static void
mail_transaction_log_file_munmap(struct mail_transaction_log_file *file)
{
    if (file->mmap_base == NULL)
        return;

    if (munmap(file->mmap_base, file->mmap_size) < 0) {
        mail_index_file_set_syscall_error(file->log->index,
                          file->filepath, "munmap()");
    }
    file->mmap_base = NULL;
    file->mmap_size = 0;
    buffer_free(&file->buffer);
}

static int
mail_transaction_log_file_map_mmap(struct mail_transaction_log_file *file,
                   uoff_t start_offset)
{
    struct stat st;
    int ret;

    /* we are going to mmap() this file, but it's not necessarily
       mmaped currently. */
    i_assert(file->buffer_offset == 0 || file->mmap_base == NULL);
    i_assert(file->mmap_size == 0 || file->mmap_base != NULL);

    if (fstat(file->fd, &st) < 0) {
        mail_index_file_set_syscall_error(file->log->index,
                          file->filepath, "fstat()");
        return -1;
    }
    file->last_size = st.st_size;

    if ((uoff_t)st.st_size < file->sync_offset) {
        mail_transaction_log_file_set_corrupted(file,
                            "file size shrank");
        return 0;
    }

    if (file->buffer != NULL && file->buffer_offset <= start_offset &&
        (uoff_t)st.st_size == file->buffer_offset + file->buffer->used) {
        /* we already have the whole file mapped */
        if ((ret = mail_transaction_log_file_sync(file)) < 0)
            return 0;
        if (ret > 0)
            return 1;
        /* size changed, re-mmap */
    }

    do {
        mail_transaction_log_file_munmap(file);

        if (file->last_size - start_offset < mmap_get_page_size()) {
            /* just reading the file is probably faster */
            return mail_transaction_log_file_read(file,
                                  start_offset,
                                  FALSE);
        }

        if (mail_transaction_log_file_mmap(file) < 0)
            return -1;
        if ((ret = mail_transaction_log_file_sync(file)) < 0)
            return 0;
    } while (ret == 0);

    return 1;
}

int mail_transaction_log_file_map(struct mail_transaction_log_file *file,
                  uoff_t start_offset, uoff_t end_offset)
{
    struct mail_index *index = file->log->index;
    size_t size;
    int ret;

    if (file->hdr.indexid == 0) {
        /* corrupted */
        return 0;
    }

    i_assert(start_offset >= file->hdr.hdr_size);
    i_assert(start_offset <= end_offset);

    if (index->log_locked && file == file->log->head &&
        end_offset == (uoff_t)-1) {
        /* we're not interested of going further than sync_offset */
        if (log_file_map_check_offsets(file, start_offset,
                           end_offset) == 0)
            return 0;
        i_assert(start_offset <= file->sync_offset);
        end_offset = file->sync_offset;
    }

    if (file->buffer != NULL && file->buffer_offset <= start_offset) {
        /* see if we already have it */
        size = buffer_get_used_size(file->buffer);
        if (file->buffer_offset + size >= end_offset)
            return 1;
    }

    if (MAIL_TRANSACTION_LOG_FILE_IN_MEMORY(file)) {
        if (start_offset < file->buffer_offset) {
            /* we had moved the log to memory but failed to read
               the beginning of the log file */
            mail_index_set_error(index,
                "%s: Beginning of the log isn't available",
                file->filepath);
            return 0;
        }
        return log_file_map_check_offsets(file, start_offset,
                          end_offset);
    }

    if (start_offset > file->sync_offset)
        mail_transaction_log_file_skip_to_head(file);
    if (start_offset > file->sync_offset) {
        /* although we could just skip over the unwanted data, we have
           to sync everything so that modseqs are calculated
           correctly */
        start_offset = file->sync_offset;
    }

    if (!index->mmap_disable)
        ret = mail_transaction_log_file_map_mmap(file, start_offset);
    else {
        mail_transaction_log_file_munmap(file);
        ret = mail_transaction_log_file_read(file, start_offset, FALSE);
    }

    return ret <= 0 ? ret :
        log_file_map_check_offsets(file, start_offset, end_offset);
}

void mail_transaction_log_file_move_to_memory(struct mail_transaction_log_file
                          *file)
{
    buffer_t *buf;

    if (MAIL_TRANSACTION_LOG_FILE_IN_MEMORY(file))
        return;

    if (file->mmap_base != NULL) {
        /* just copy to memory */
        i_assert(file->buffer_offset == 0);

        buf = buffer_create_dynamic(default_pool, file->mmap_size);
        buffer_append(buf, file->mmap_base, file->mmap_size);
        buffer_free(&file->buffer);
        file->buffer = buf;

        /* and lose the mmap */
        if (munmap(file->mmap_base, file->mmap_size) < 0) {
            mail_index_file_set_syscall_error(file->log->index,
                              file->filepath,
                              "munmap()");
        }
        file->mmap_base = NULL;
    } else if (file->buffer_offset != 0) {
        /* we don't have the full log in the memory. read it. */
        (void)mail_transaction_log_file_read(file, 0, FALSE);
    }
    file->last_size = 0;

    if (close(file->fd) < 0) {
        mail_index_file_set_syscall_error(file->log->index,
                          file->filepath, "close()");
    }
    file->fd = -1;

    i_free(file->filepath);
    file->filepath = i_strconcat(file->log->index->filepath,
                     MAIL_TRANSACTION_LOG_SUFFIX, NULL);
}