index/maildir/maildir-sync.c

	maildir-sync.c revision d3eff05aaa4c2bc0a7580ee87a54f6693f4a8241
c25356d5978632df6203437e1953bcb29e0c736fTimo Sirainen/* Copyright (C) 2004 Timo Sirainen */
c25356d5978632df6203437e1953bcb29e0c736fTimo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen/*
cfdaa223525f87c9c980a25cc7bb6770a248d76aTimo Sirainen   Here's a description of how we handle Maildir synchronization and
cfdaa223525f87c9c980a25cc7bb6770a248d76aTimo Sirainen   it's problems:
cfdaa223525f87c9c980a25cc7bb6770a248d76aTimo Sirainen
cfdaa223525f87c9c980a25cc7bb6770a248d76aTimo Sirainen   We want to be as efficient as we can. The most efficient way to
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   check if changes have occurred is to stat() the new/ and cur/
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   directories and uidlist file - if their mtimes haven't changed,
3c9783956dea385b322cd7fa6bf8c98c17a907a0Timo Sirainen   there's no changes and we don't need to do anything.
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   Problem 1: Multiple changes can happen within a single second -
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   nothing guarantees that once we synced it, someone else didn't just
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   then make a modification. Such modifications wouldn't get noticed
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   until a new modification occurred later.
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   Problem 2: Syncing cur/ directory is much more costly than syncing
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   new/. Moving mails from new/ to cur/ will always change mtime of
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   cur/ causing us to sync it as well.
e65cc79f80577e83c706f0678c78e2c0bd91434fTimo Sirainen
7d6389e4053c2dac1fb37180b5756b00785983dcTimo Sirainen   Problem 3: We may not be able to move mail from new/ to cur/
7d6389e4053c2dac1fb37180b5756b00785983dcTimo Sirainen   because we're out of quota, or simply because we're accessing a
6ef7e31619edfaa17ed044b45861d106a86191efTimo Sirainen   read-only mailbox.
f1ddb98e6b639394ae205b305be1ddcfab102578Timo Sirainen
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen
40992309053d51192ae1b36d1dd6c057f2d37257Timo Sirainen   MAILDIR_SYNC_SECS
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   -----------------
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   Several checks below use MAILDIR_SYNC_SECS, which should be maximum
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   clock drift between all computers accessing the maildir (eg. via
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   NFS), rounded up to next second. Our default is 1 second, since
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   everyone should be using NTP.
e82af44fe25ca9b88210f313548dc08538e4a677Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   Note that setting it to 0 works only if there's only one computer
b567e0172c73dcf7642462e86962060358dd5f28Timo Sirainen   accessing the maildir. It's practically impossible to make two
b567e0172c73dcf7642462e86962060358dd5f28Timo Sirainen   clocks _exactly_ synchronized.
10c5fd417af4ee30b68c967f5e7d5a49f4f149b5Timo Sirainen
10c5fd417af4ee30b68c967f5e7d5a49f4f149b5Timo Sirainen   It might be possible to only use file server's clock by looking at
10c5fd417af4ee30b68c967f5e7d5a49f4f149b5Timo Sirainen   the atime field, but I don't know how well that would actually work.
10c5fd417af4ee30b68c967f5e7d5a49f4f149b5Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   cur directory
473080c7c0d25ddfdf77e7dfa0ba8f73c6c669d5Timo Sirainen   -------------
1f18053d463f0294387b5e4dd11f9010bda9a24eTimo Sirainen
6ef7e31619edfaa17ed044b45861d106a86191efTimo Sirainen   We have dirty_cur_time variable which is set to cur/ directory's
e82af44fe25ca9b88210f313548dc08538e4a677Timo Sirainen   mtime when it's >= time() - MAILDIR_SYNC_SECS and we _think_ we have
e714eed72515794c46c6712a611e5ab924d903daTimo Sirainen   synchronized the directory.
e714eed72515794c46c6712a611e5ab924d903daTimo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   When dirty_cur_time is non-zero, we don't synchronize the cur/
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   directory until
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen
c4457e497e01b57565d24da624968699b166e02aTimo Sirainen      a) cur/'s mtime changes
c4457e497e01b57565d24da624968699b166e02aTimo Sirainen      b) opening a mail fails with ENOENT
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen      c) time() > dirty_cur_time + MAILDIR_SYNC_SECS
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   This allows us to modify the maildir multiple times without having
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   to sync it at every change. The sync will eventually be done to
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   make sure we didn't miss any external changes.
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   The dirty_cur_time is set when:
b270b29d458f3cbd6e63320bb17e23f809da0045Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen      - we change message flags
e023e3c2677ab66d7a7445eae9caf3d739e199cbTimo Sirainen      - we expunge messages
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen      - we move mail from new/ to cur/
e023e3c2677ab66d7a7445eae9caf3d739e199cbTimo Sirainen      - we sync cur/ directory and it's mtime is >= time() - MAILDIR_SYNC_SECS
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen
0d7d27765267594a5870892268ab345148306d49Timo Sirainen   It's unset when we do the final syncing, ie. when mtime is
0d7d27765267594a5870892268ab345148306d49Timo Sirainen   older than time() - MAILDIR_SYNC_SECS.
9f431ccfb6932746db56245c8a3d3415717ef545Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   new directory
16133a719ce8b6a5b8cedd721340cc1607c43433Timo Sirainen   -------------
ecb1b2d6236942bf82f822e8d0167f0e160b206dTimo Sirainen
16133a719ce8b6a5b8cedd721340cc1607c43433Timo Sirainen   If new/'s mtime is >= time() - MAILDIR_SYNC_SECS, always synchronize
16133a719ce8b6a5b8cedd721340cc1607c43433Timo Sirainen   it. dirty_cur_time-like feature might save us a few syncs, but
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   that might break a client which saves a mail in one connection and
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   tries to fetch it in another one. new/ directory is almost always
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   empty, so syncing it should be very fast anyway. Actually this can
e023e3c2677ab66d7a7445eae9caf3d739e199cbTimo Sirainen   still happen if we sync only new/ dir while another client is also
e023e3c2677ab66d7a7445eae9caf3d739e199cbTimo Sirainen   moving mails from it to cur/ - it takes us a while to see them.
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   That's pretty unlikely to happen however, and only way to fix it
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   would be to always synchronize cur/ after new/.
ed5e91e58dfc372c2135c55427bf6f25a7725042Timo Sirainen
16133a719ce8b6a5b8cedd721340cc1607c43433Timo Sirainen   Normally we move all mails from new/ to cur/ whenever we sync it. If
ed5e91e58dfc372c2135c55427bf6f25a7725042Timo Sirainen   it's not possible for some reason, we mark the mail with "probably
ed5e91e58dfc372c2135c55427bf6f25a7725042Timo Sirainen   exists in new/ directory" flag.
ed5e91e58dfc372c2135c55427bf6f25a7725042Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   If rename() still fails because of ENOSPC or EDQUOT, we still save
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   the flag changes in index with dirty-flag on. When moving the mail
dd2d3ef41dc407afb8afc49e18ff53640e4b4e02Timo Sirainen   to cur/ directory, or when we notice it's already moved there, we
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   apply the flag changes to the filename, rename it and remove the
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   dirty flag. If there's dirty flags, this should be tried every time
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   after expunge or when closing the mailbox.
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   uidlist
a399486f2d8d5bed51bc6344baba61a7f2b0dcdbTimo Sirainen   -------
e023e3c2677ab66d7a7445eae9caf3d739e199cbTimo Sirainen
e023e3c2677ab66d7a7445eae9caf3d739e199cbTimo Sirainen   This file contains UID <-> filename mappings. It's updated only when
25ee72451d16374ed27fdbf829f4ec756c778352Timo Sirainen   new mail arrives, so it may contain filenames that have already been
25ee72451d16374ed27fdbf829f4ec756c778352Timo Sirainen   deleted. Updating is done by getting uidlist.lock file, writing the
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   whole uidlist into it and rename()ing it over the old uidlist. This
9f431ccfb6932746db56245c8a3d3415717ef545Timo Sirainen   means there's no need to lock the file for reading.
0d7d27765267594a5870892268ab345148306d49Timo Sirainen
16133a719ce8b6a5b8cedd721340cc1607c43433Timo Sirainen   Whenever uidlist is rewritten, it's mtime must be larger than the old
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   one's. Use utime() before rename() if needed. Note that inode checking
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   wouldn't have been sufficient as inode numbers can be reused.
d5cebe7f98e63d4e2822863ef2faa4971e8b3a5dTimo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   This file is usually read the first time you need to know filename for
16133a719ce8b6a5b8cedd721340cc1607c43433Timo Sirainen   given UID. After that it's not re-read unless new mails come that we
08aea01ef9a9d20703e0fcf8618e6195c0037a44Timo Sirainen   don't know about.
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   broken clients
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   --------------
3c9783956dea385b322cd7fa6bf8c98c17a907a0Timo Sirainen
3c9783956dea385b322cd7fa6bf8c98c17a907a0Timo Sirainen   Originally the middle identifier in Maildir filename was specified
ebfcfd258acc89633c47d9c3b0b40a1a3f75cdcbTimo Sirainen   only as <process id>_<delivery counter>. That however created a
d1f0acc7fc722e13e8296228703adfe8a884d59eTimo Sirainen   problem with randomized PIDs which made it possible that the same
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   PID was reused within one second.
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   So if within one second a mail was delivered, MUA moved it to cur/
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   and another mail was delivered by a new process using same PID as
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   the first one, we likely ended up overwriting the first mail when
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   the second mail was moved over it.
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   Nowadays everyone should be giving a bit more specific identifier,
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen   for example include microseconds in it which Dovecot does.
4261a8b43792dc4db4b39e6910319835b7450e84Timo Sirainen
965ed6ea3fc8f7637bd0d159d2fdb283a191ce34Timo Sirainen   There's a simple way to prevent this from happening in some cases:
   Don't move the mail from new/ to cur/ if it's mtime is >= time() -
   MAILDIR_SYNC_SECS. The second delivery's link() call then fails
   because the file is already in new/, and it will then use a
   different filename. There's a few problems with this however:

      - it requires extra stat() call which is unneeded extra I/O
      - another MUA might still move the mail to cur/
      - if first file's flags are modified by either Dovecot or another
        MUA, it's moved to cur/ (you _could_ just do the dirty-flagging
    but that'd be ugly)

   Because this is useful only for very few people and it requires
   extra I/O, I decided not to implement this. It should be however
   quite easy to do since we need to be able to deal with files in new/
   in any case.

   It's also possible to never accidentally overwrite a mail by using
   link() + unlink() rather than rename(). This however isn't very
   good idea as it introduces potential race conditions when multiple
   clients are accessing the mailbox:

   Trying to move the same mail from new/ to cur/ at the same time:

      a) Client 1 uses slightly different filename than client 2,
         for example one sets read-flag on but the other doesn't.
     You have the same mail duplicated now.

      b) Client 3 sees the mail between Client 1's and 2's link() calls
         and changes it's flag. You have the same mail duplicated now.

   And it gets worse when they're unlink()ing in cur/ directory:

      c) Client 1 changes mails's flag and client 2 changes it back
         between 1's link() and unlink(). The mail is now expunged.

      d) If you try to deal with the duplicates by unlink()ing another
         one of them, you might end up unlinking both of them.

   So, what should we do then if we notice a duplicate? First of all,
   it might not be a duplicate at all, readdir() might have just
   returned it twice because it was just renamed. What we should do is
   create a completely new base name for it and rename() it to that.
   If the call fails with ENOENT, it only means that it wasn't a
   duplicate after all.
*/

#include "lib.h"
#include "ioloop.h"
#include "array.h"
#include "buffer.h"
#include "hash.h"
#include "str.h"
#include "maildir-storage.h"
#include "maildir-uidlist.h"
#include "maildir-keywords.h"
#include "maildir-sync.h"

#include <stdio.h>
#include <stddef.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/stat.h>

#define MAILDIR_FILENAME_FLAG_FOUND 128

/* When rename()ing many files from new/ to cur/, it's possible that next
   readdir() skips some files. we don't of course wish to lose them, so we
   go and rescan the new/ directory again from beginning until no files are
   left. This value is just an optimization to avoid checking the directory
   twice unneededly. usually only NFS is the problem case. 1 is the safest
   bet here, but I guess 5 will do just fine too. */
#define MAILDIR_RENAME_RESCAN_COUNT 5

/* After moving 100 mails from new/ to cur/, check if we need to touch the
   uidlist lock. */
#define MAILDIR_SLOW_MOVE_COUNT 100
/* readdir() should be pretty fast to do, but check anyway every 10000 mails
   to see if we need to touch the uidlist lock. */
#define MAILDIR_SLOW_CHECK_COUNT 10000

struct maildir_sync_context {
        struct maildir_mailbox *mbox;
    const char *new_dir, *cur_dir;
    bool partial;

    struct maildir_uidlist_sync_ctx *uidlist_sync_ctx;
        struct maildir_index_sync_context *index_sync_ctx;
};

struct maildir_index_sync_context {
        struct maildir_mailbox *mbox;
    struct mail_index_view *view;
    struct mail_index_sync_ctx *sync_ctx;
        struct maildir_keywords_sync_ctx *keywords_sync_ctx;
    struct mail_index_transaction *trans;

    ARRAY_DEFINE(sync_recs, struct mail_index_sync_rec);
    uint32_t seq;
    int dirty_state;
};

struct maildir_keywords_sync_ctx *
maildir_sync_get_keywords_sync_ctx(struct maildir_index_sync_context *ctx)
{
    return ctx->keywords_sync_ctx;
}

int maildir_filename_get_flags(struct maildir_keywords_sync_ctx *ctx,
                   const char *fname, enum mail_flags *flags_r,
                               ARRAY_TYPE(keyword_indexes) *keywords_r)
{
    const char *info;

    array_clear(keywords_r);
    *flags_r = 0;

    info = strchr(fname, MAILDIR_INFO_SEP);
    if (info == NULL || info[1] != '2' || info[2] != MAILDIR_FLAGS_SEP)
        return 0;

    for (info += 3; *info != '\0' && *info != MAILDIR_FLAGS_SEP; info++) {
        switch (*info) {
        case 'R': /* replied */
            *flags_r |= MAIL_ANSWERED;
            break;
        case 'S': /* seen */
            *flags_r |= MAIL_SEEN;
            break;
        case 'T': /* trashed */
            *flags_r |= MAIL_DELETED;
            break;
        case 'D': /* draft */
            *flags_r |= MAIL_DRAFT;
            break;
        case 'F': /* flagged */
            *flags_r |= MAIL_FLAGGED;
            break;
        default:
            if (*info >= MAILDIR_KEYWORD_FIRST &&
                *info <= MAILDIR_KEYWORD_LAST) {
                int idx;

                idx = maildir_keywords_char_idx(ctx, *info);
                if (idx < 0) {
                    /* unknown keyword. */
                    break;
                }

                array_append(keywords_r,
                         (unsigned int *)&idx, 1);
                break;
            }

            /* unknown flag - ignore */
            break;
        }
    }

    return 1;
}

static void
maildir_filename_append_keywords(struct maildir_keywords_sync_ctx *ctx,
                 ARRAY_TYPE(keyword_indexes) *keywords,
                 string_t *str)
{
    const unsigned int *indexes;
    unsigned int i, count;
    char chr;

    indexes = array_get(keywords, &count);
    for (i = 0; i < count; i++) {
        chr = maildir_keywords_idx_char(ctx, indexes[i]);
        if (chr != '\0')
            str_append_c(str, chr);
    }
}

const char *maildir_filename_set_flags(struct maildir_keywords_sync_ctx *ctx,
                       const char *fname, enum mail_flags flags,
                       ARRAY_TYPE(keyword_indexes) *keywords)
{
    string_t *flags_str;
    enum mail_flags flags_left;
    const char *info, *oldflags;
    int nextflag;

    /* remove the old :info from file name, and get the old flags */
    info = strrchr(fname, MAILDIR_INFO_SEP);
    if (info != NULL && strrchr(fname, '/') > info)
        info = NULL;

    oldflags = "";
    if (info != NULL) {
        fname = t_strdup_until(fname, info);
        if (info[1] == '2' && info[2] == MAILDIR_FLAGS_SEP)
            oldflags = info+3;
    }

    /* insert the new flags between old flags. flags must be sorted by
       their ASCII code. unknown flags are kept. */
    flags_str = t_str_new(256);
    str_append(flags_str, fname);
    str_append(flags_str, MAILDIR_FLAGS_FULL_SEP);
    flags_left = flags;
    for (;;) {
        /* skip all known flags */
        while (*oldflags == 'D' || *oldflags == 'F' ||
               *oldflags == 'R' || *oldflags == 'S' ||
               *oldflags == 'T' ||
               (*oldflags >= MAILDIR_KEYWORD_FIRST &&
            *oldflags <= MAILDIR_KEYWORD_LAST))
            oldflags++;

        nextflag = *oldflags == '\0' || *oldflags == MAILDIR_FLAGS_SEP ?
            256 : (unsigned char) *oldflags;

        if ((flags_left & MAIL_DRAFT) && nextflag > 'D') {
            str_append_c(flags_str, 'D');
            flags_left &= ~MAIL_DRAFT;
        }
        if ((flags_left & MAIL_FLAGGED) && nextflag > 'F') {
            str_append_c(flags_str, 'F');
            flags_left &= ~MAIL_FLAGGED;
        }
        if ((flags_left & MAIL_ANSWERED) && nextflag > 'R') {
            str_append_c(flags_str, 'R');
            flags_left &= ~MAIL_ANSWERED;
        }
        if ((flags_left & MAIL_SEEN) && nextflag > 'S') {
            str_append_c(flags_str, 'S');
            flags_left &= ~MAIL_SEEN;
        }
        if ((flags_left & MAIL_DELETED) && nextflag > 'T') {
            str_append_c(flags_str, 'T');
            flags_left &= ~MAIL_DELETED;
        }

        if (keywords != NULL && array_is_created(keywords) &&
            nextflag > MAILDIR_KEYWORD_FIRST) {
            maildir_filename_append_keywords(ctx, keywords,
                             flags_str);
            keywords = NULL;
        }

        if (*oldflags == '\0' || *oldflags == MAILDIR_FLAGS_SEP)
            break;

        str_append_c(flags_str, *oldflags);
        oldflags++;
    }

    if (*oldflags == MAILDIR_FLAGS_SEP) {
        /* another flagset, we don't know about these, just keep them */
        while (*oldflags != '\0')
            str_append_c(flags_str, *oldflags++);
    }

    return str_c(flags_str);
}

static int maildir_expunge(struct maildir_mailbox *mbox, const char *path,
               void *context __attr_unused__)
{
    if (unlink(path) == 0) {
        mbox->dirty_cur_time = ioloop_time;
        return 1;
    }
    if (errno == ENOENT)
        return 0;

    mail_storage_set_critical(STORAGE(mbox->storage),
                  "unlink(%s) failed: %m", path);
    return -1;
}

static int maildir_sync_flags(struct maildir_mailbox *mbox, const char *path,
                  struct maildir_index_sync_context *ctx)
{
    const struct mail_index_sync_rec *recs;
    const char *dir, *fname, *newfname, *newpath;
    enum mail_flags flags;
    ARRAY_TYPE(keyword_indexes) keywords;
    unsigned int i, count;
    uint8_t flags8;

    ctx->dirty_state = 0;

    fname = strrchr(path, '/');
    i_assert(fname != NULL);
    fname++;
    dir = t_strdup_until(path, fname);

    t_array_init(&keywords, 16);
    (void)maildir_filename_get_flags(ctx->keywords_sync_ctx,
                     fname, &flags, &keywords);
    flags8 = flags;

    recs = array_get_modifiable(&ctx->sync_recs, &count);
    for (i = 0; i < count; i++) {
        if (recs[i].uid1 != ctx->seq)
            break;

        switch (recs[i].type) {
        case MAIL_INDEX_SYNC_TYPE_FLAGS:
            mail_index_sync_flags_apply(&recs[i], &flags8);
            break;
        case MAIL_INDEX_SYNC_TYPE_KEYWORD_ADD:
        case MAIL_INDEX_SYNC_TYPE_KEYWORD_REMOVE:
        case MAIL_INDEX_SYNC_TYPE_KEYWORD_RESET:
            mail_index_sync_keywords_apply(&recs[i], &keywords);
            break;
        case MAIL_INDEX_SYNC_TYPE_APPEND:
        case MAIL_INDEX_SYNC_TYPE_EXPUNGE:
            i_unreached();
            break;
        }
    }


    newfname = maildir_filename_set_flags(ctx->keywords_sync_ctx,
                          fname, flags8, &keywords);
    newpath = t_strconcat(dir, newfname, NULL);
    if (rename(path, newpath) == 0) {
        if ((flags8 & MAIL_INDEX_MAIL_FLAG_DIRTY) != 0)
            ctx->dirty_state = -1;
        mbox->dirty_cur_time = ioloop_time;
        return 1;
    }
    if (errno == ENOENT)
        return 0;

    if (ENOSPACE(errno) || errno == EACCES) {
        mail_index_update_flags(ctx->trans, ctx->seq, MODIFY_ADD,
                    MAIL_INDEX_MAIL_FLAG_DIRTY);
        ctx->dirty_state = 1;
        return 1;
    }

    mail_storage_set_critical(STORAGE(mbox->storage),
                  "rename(%s, %s) failed: %m", path, newpath);
    return -1;
}

static int
maildir_sync_record_commit_until(struct maildir_index_sync_context *ctx,
                 uint32_t last_seq)
{
    struct mail_index_sync_rec *recs;
    unsigned int i, count;
    uint32_t seq, uid;
    bool expunged, flag_changed;

    recs = array_get_modifiable(&ctx->sync_recs, &count);
    for (seq = recs[0].uid1; seq <= last_seq; seq++) {
        expunged = flag_changed = FALSE;
        for (i = 0; i < count; i++) {
            if (recs[i].uid1 > seq)
                break;

            i_assert(recs[i].uid1 == seq);
            switch (recs[i].type) {
            case MAIL_INDEX_SYNC_TYPE_EXPUNGE:
                expunged = TRUE;
                break;
            case MAIL_INDEX_SYNC_TYPE_FLAGS:
            case MAIL_INDEX_SYNC_TYPE_KEYWORD_ADD:
            case MAIL_INDEX_SYNC_TYPE_KEYWORD_REMOVE:
            case MAIL_INDEX_SYNC_TYPE_KEYWORD_RESET:
                flag_changed = TRUE;
                break;
            case MAIL_INDEX_SYNC_TYPE_APPEND:
                i_unreached();
                break;
            }
        }

        if (mail_index_lookup_uid(ctx->view, seq, &uid) < 0) {
            mail_storage_set_index_error(&ctx->mbox->ibox);
            return -1;
        }

        ctx->seq = seq;
        if (expunged) {
            if (maildir_file_do(ctx->mbox, uid,
                        maildir_expunge, ctx) < 0)
                return -1;
        } else if (flag_changed) {
            if (maildir_file_do(ctx->mbox, uid,
                        maildir_sync_flags, ctx) < 0)
                return -1;
        }

        for (i = count; i > 0; i--) {
            if (++recs[i-1].uid1 > recs[i-1].uid2) {
                array_delete(&ctx->sync_recs, i-1, 1);
                recs = array_get_modifiable(&ctx->sync_recs,
                                &count);
                if (count == 0) {
                    /* all sync_recs committed */
                    return 0;
                }
            }
        }
    }
    return 0;
}

static int maildir_sync_record(struct maildir_index_sync_context *ctx,
                   const struct mail_index_sync_rec *sync_rec)
{
    struct mail_index_view *view = ctx->view;
        struct mail_index_sync_rec sync_copy;

    if (sync_rec == NULL) {
        /* deinit */
        while (array_count(&ctx->sync_recs) > 0) {
            if (maildir_sync_record_commit_until(ctx,
                                 (uint32_t)-1) < 0)
                return -1;
        }
        return 0;
    }

    if (sync_rec->type == MAIL_INDEX_SYNC_TYPE_APPEND)
        return 0; /* ignore */

    /* convert to sequences to avoid looping through huge holes in
       UID range */
        sync_copy = *sync_rec;
    if (mail_index_lookup_uid_range(view, sync_rec->uid1,
                    sync_rec->uid2,
                    &sync_copy.uid1,
                    &sync_copy.uid2) < 0) {
        mail_storage_set_index_error(&ctx->mbox->ibox);
        return -1;
    }

    if (sync_copy.uid1 == 0) {
        /* UIDs were expunged */
        return 0;
    }

    while (array_count(&ctx->sync_recs) > 0) {
        const struct mail_index_sync_rec *rec =
            array_idx(&ctx->sync_recs, 0);

        i_assert(rec->uid1 <= sync_copy.uid1);
        if (rec->uid1 == sync_copy.uid1)
            break;

        if (maildir_sync_record_commit_until(ctx, sync_copy.uid1-1) < 0)
            return -1;
    }

    array_append(&ctx->sync_recs, &sync_copy, 1);
    return 0;
}

static int maildir_sync_index_records(struct maildir_index_sync_context *ctx)
{
    struct mail_index_sync_rec sync_rec;
    int ret;

    ret = mail_index_sync_next(ctx->sync_ctx, &sync_rec);
    if (ret <= 0) {
        if (ret < 0)
            mail_storage_set_index_error(&ctx->mbox->ibox);
        return ret;
    }

    t_array_init(&ctx->sync_recs, 32);
    do {
        if (maildir_sync_record(ctx, &sync_rec) < 0)
            return -1;

        ret = mail_index_sync_next(ctx->sync_ctx, &sync_rec);
    } while (ret > 0);

    if (ret < 0)
        mail_storage_set_index_error(&ctx->mbox->ibox);

    if (maildir_sync_record(ctx, NULL) < 0)
        return -1;
    return ret;
}

static struct maildir_sync_context *
maildir_sync_context_new(struct maildir_mailbox *mbox)
{
        struct maildir_sync_context *ctx;

    ctx = t_new(struct maildir_sync_context, 1);
    ctx->mbox = mbox;
    ctx->new_dir = t_strconcat(mbox->path, "/new", NULL);
    ctx->cur_dir = t_strconcat(mbox->path, "/cur", NULL);
    return ctx;
}

static void maildir_sync_deinit(struct maildir_sync_context *ctx)
{
    if (ctx->uidlist_sync_ctx != NULL)
        (void)maildir_uidlist_sync_deinit(&ctx->uidlist_sync_ctx);
    if (ctx->index_sync_ctx != NULL) {
        (void)maildir_sync_index_finish(&ctx->index_sync_ctx,
                        TRUE, FALSE);
    }
}

static int maildir_fix_duplicate(struct maildir_sync_context *ctx,
                 const char *dir, const char *old_fname)
{
    struct maildir_mailbox *mbox = ctx->mbox;
    const char *existing_fname, *existing_path;
    const char *new_fname, *old_path, *new_path;
    struct stat st, st2;
    int ret = 0;

    existing_fname =
        maildir_uidlist_sync_get_full_filename(ctx->uidlist_sync_ctx,
                               old_fname);
    i_assert(existing_fname != NULL);

    t_push();

    existing_path = t_strconcat(dir, "/", existing_fname, NULL);
    old_path = t_strconcat(dir, "/", old_fname, NULL);

    if (stat(existing_path, &st) < 0 ||
        stat(old_path, &st2) < 0) {
        /* most likely the files just don't exist anymore.
           don't really care about other errors much. */
        t_pop();
        return 0;
    }
    if (st.st_ino == st2.st_ino && CMP_DEV_T(st.st_dev, st2.st_dev)) {
        /* files are the same. this means either a race condition
           between stat() calls, or someone has started link()ing the
           files. either way there's no data loss if we just leave it
           there. */
        t_pop();
        return 0;
    }

    new_fname = maildir_generate_tmp_filename(&ioloop_timeval);
    new_path = t_strconcat(mbox->path, "/new/", new_fname, NULL);

    if (rename(old_path, new_path) == 0) {
        i_warning("Fixed duplicate in %s: %s -> %s",
              mbox->path, old_fname, new_fname);
    } else if (errno != ENOENT) {
        mail_storage_set_critical(STORAGE(mbox->storage),
            "rename(%s, %s) failed: %m", old_path, new_path);
        ret = -1;
    }
    t_pop();

    return ret;
}

static int maildir_scan_dir(struct maildir_sync_context *ctx, bool new_dir)
{
    struct mail_storage *storage = STORAGE(ctx->mbox->storage);
    const char *dir;
    DIR *dirp;
    string_t *src, *dest;
    struct dirent *dp;
    enum maildir_uidlist_rec_flag flags;
    time_t last_touch;
    unsigned int moves = 0, count = 0;
    int ret = 1;
    bool move_new, check_touch;

    last_touch = ioloop_time;

    dir = new_dir ? ctx->new_dir : ctx->cur_dir;
    dirp = opendir(dir);
    if (dirp == NULL) {
        mail_storage_set_critical(storage,
                      "opendir(%s) failed: %m", dir);
        return -1;
    }

    t_push();
    src = t_str_new(1024);
    dest = t_str_new(1024);

    move_new = new_dir && !mailbox_is_readonly(&ctx->mbox->ibox.box) &&
        !ctx->mbox->ibox.keep_recent;
    while ((dp = readdir(dirp)) != NULL) {
        if (dp->d_name[0] == '.')
            continue;

        ret = maildir_uidlist_sync_next_pre(ctx->uidlist_sync_ctx,
                            dp->d_name);
        if (ret == 0) {
            /* new file and we couldn't lock uidlist, check this
               later in next sync. */
            if (new_dir)
                ctx->mbox->last_new_mtime = 0;
            else
                ctx->mbox->dirty_cur_time = ioloop_time;
            continue;
        }
        if (ret < 0)
            break;

        check_touch = FALSE;
        flags = 0;
        if (move_new) {
            str_truncate(src, 0);
            str_truncate(dest, 0);
            str_printfa(src, "%s/%s", ctx->new_dir, dp->d_name);
            str_printfa(dest, "%s/%s", ctx->cur_dir, dp->d_name);
            if (strchr(dp->d_name, MAILDIR_INFO_SEP) == NULL) {
                str_append(dest, MAILDIR_FLAGS_FULL_SEP);
            }
            if (rename(str_c(src), str_c(dest)) == 0) {
                /* we moved it - it's \Recent for us */
                moves++;
                ctx->mbox->dirty_cur_time = ioloop_time;
                flags |= MAILDIR_UIDLIST_REC_FLAG_MOVED |
                    MAILDIR_UIDLIST_REC_FLAG_RECENT;
            } else if (ENOTFOUND(errno)) {
                /* someone else moved it already */
                moves++;
                flags |= MAILDIR_UIDLIST_REC_FLAG_MOVED;
            } else if (ENOSPACE(errno) || errno == EACCES) {
                /* not enough disk space / read-only maildir,
                   leave here */
                flags |= MAILDIR_UIDLIST_REC_FLAG_NEW_DIR |
                    MAILDIR_UIDLIST_REC_FLAG_RECENT;
                move_new = FALSE;
            } else {
                flags |= MAILDIR_UIDLIST_REC_FLAG_NEW_DIR |
                    MAILDIR_UIDLIST_REC_FLAG_RECENT;
                mail_storage_set_critical(storage,
                    "rename(%s, %s) failed: %m",
                    str_c(src), str_c(dest));
            }
            if ((moves % MAILDIR_SLOW_MOVE_COUNT) == 0)
                check_touch = TRUE;
        } else if (new_dir) {
            flags |= MAILDIR_UIDLIST_REC_FLAG_NEW_DIR |
                MAILDIR_UIDLIST_REC_FLAG_RECENT;
        }

        count++;
        if (check_touch || (count % MAILDIR_SLOW_CHECK_COUNT) == 0) {
            time_t now = time(NULL);

            if (now - last_touch > MAILDIR_LOCK_TOUCH_SECS) {
                (void)maildir_uidlist_lock_touch(
                            ctx->mbox->uidlist);
                last_touch = now;
            }
        }

        ret = maildir_uidlist_sync_next(ctx->uidlist_sync_ctx,
                        dp->d_name, flags);
        if (ret <= 0) {
            if (ret < 0)
                break;

            /* possibly duplicate - try fixing it */
            if (maildir_fix_duplicate(ctx, dir, dp->d_name) < 0) {
                ret = -1;
                break;
            }
        }
    }

    if (closedir(dirp) < 0) {
        mail_storage_set_critical(storage,
                      "closedir(%s) failed: %m", dir);
    }

    t_pop();
    return ret < 0 ? -1 : (moves <= MAILDIR_RENAME_RESCAN_COUNT ? 0 : 1);
}

static void
maildir_sync_update_from_header(struct maildir_mailbox *mbox,
                struct mail_index_header *hdr_r)
{
    struct mail_index_view *view;
    const struct mail_index_header *hdr;

    /* open a new view so we get the latest header */
    view = mail_index_view_open(mbox->ibox.index);
    hdr = mail_index_get_header(view);

    /* FIXME: ugly, replace with extension header */
    mbox->last_new_mtime = hdr->sync_size & 0xffffffff;
    mbox->last_dirty_flags = (hdr->sync_size >> 32) &
        (MAILDIR_DIRTY_NEW | MAILDIR_DIRTY_CUR);

    mbox->last_cur_mtime = hdr->sync_stamp;

    if ((mbox->last_dirty_flags & MAILDIR_DIRTY_CUR) != 0 &&
        mbox->dirty_cur_time < mbox->last_cur_mtime)
        mbox->dirty_cur_time = mbox->last_cur_mtime;

    *hdr_r = *hdr;
    mail_index_view_close(&view);
}

static int
maildir_sync_quick_check(struct maildir_mailbox *mbox,
             const char *new_dir, const char *cur_dir,
             bool *new_changed_r, bool *cur_changed_r)
{
    struct index_mailbox *ibox = &mbox->ibox;
    struct mail_index_header hdr;
    struct stat st;
    time_t new_mtime, cur_mtime;

    *new_changed_r = *cur_changed_r = FALSE;

    if (stat(new_dir, &st) < 0) {
        mail_storage_set_critical(STORAGE(mbox->storage),
                      "stat(%s) failed: %m", new_dir);
        return -1;
    }
    new_mtime = st.st_mtime;

    if (stat(cur_dir, &st) < 0) {
        mail_storage_set_critical(STORAGE(mbox->storage),
                      "stat(%s) failed: %m", cur_dir);
        return -1;
    }
    cur_mtime = st.st_mtime;

    /* cur stamp is kept in index, we don't have to sync if
       someone else has done it and updated the index.

       FIXME: For now we're using sync_size field as the new/ dir's stamp.
       Pretty ugly.. */
        maildir_sync_update_from_header(mbox, &hdr);
    if ((mbox->dirty_cur_time == 0 && cur_mtime != mbox->last_cur_mtime) ||
        (new_mtime != mbox->last_new_mtime)) {
        /* check if the index has been updated.. */
        if (mail_index_refresh(ibox->index) < 0) {
            mail_storage_set_index_error(ibox);
            return -1;
        }

        maildir_sync_update_from_header(mbox, &hdr);
    }

    /* If we're removing recent flags, always sync new/ directory if
       it has mails. */
    if (new_mtime != mbox->last_new_mtime ||
        ((mbox->last_dirty_flags & MAILDIR_DIRTY_NEW) != 0 &&
         new_mtime < ioloop_time - MAILDIR_SYNC_SECS) ||
        (!ibox->keep_recent && hdr.recent_messages_count > 0)) {
        *new_changed_r = TRUE;
        mbox->last_new_mtime = new_mtime;

        if (new_mtime < ioloop_time - MAILDIR_SYNC_SECS)
            mbox->last_dirty_flags &= ~MAILDIR_DIRTY_NEW;
        else
            mbox->last_dirty_flags |= MAILDIR_DIRTY_NEW;
    }

    if (cur_mtime != mbox->last_cur_mtime ||
        (mbox->dirty_cur_time != 0 &&
         ioloop_time - mbox->dirty_cur_time > MAILDIR_SYNC_SECS)) {
        /* cur/ changed, or delayed cur/ check */
        *cur_changed_r = TRUE;
        mbox->last_cur_mtime = cur_mtime;

        if (cur_mtime < ioloop_time - MAILDIR_SYNC_SECS) {
            mbox->last_dirty_flags &= ~MAILDIR_DIRTY_CUR;
            mbox->dirty_cur_time = 0;
        } else {
            mbox->last_dirty_flags |= MAILDIR_DIRTY_CUR;
            mbox->dirty_cur_time = cur_mtime;
        }
    }

    return 0;
}

int maildir_sync_index_begin(struct maildir_mailbox *mbox,
                 struct maildir_index_sync_context **ctx_r)
{
    struct maildir_index_sync_context *ctx;
    struct mail_index_sync_ctx *sync_ctx;
    struct mail_index_view *view;

    if (mail_index_sync_begin(mbox->ibox.index, &sync_ctx, &view,
                  (uint32_t)-1, (uoff_t)-1,
                  FALSE, FALSE) <= 0) {
        mail_storage_set_index_error(&mbox->ibox);
        return -1;
    }

    ctx = i_new(struct maildir_index_sync_context, 1);
    ctx->mbox = mbox;
    ctx->sync_ctx = sync_ctx;
    ctx->view = view;
    ctx->keywords_sync_ctx =
        maildir_keywords_sync_init(mbox->keywords, mbox->ibox.index);
    *ctx_r = ctx;
    return 0;
}

int maildir_sync_index_finish(struct maildir_index_sync_context **_sync_ctx,
                  bool failed, bool cancel)
{
    struct maildir_index_sync_context *sync_ctx = *_sync_ctx;
    struct maildir_mailbox *mbox = sync_ctx->mbox;
    uint32_t seq;
    uoff_t offset;
    int ret = failed ? -1 : 0;

    *_sync_ctx = NULL;

    if (sync_ctx->trans != NULL) {
        if (ret < 0 || cancel)
            mail_index_transaction_rollback(&sync_ctx->trans);
        else {
            if (mail_index_transaction_commit(&sync_ctx->trans,
                              &seq, &offset) < 0) {
                mail_storage_set_index_error(&mbox->ibox);
                ret = -1;
            } else if (seq != 0) {
                mbox->ibox.commit_log_file_seq = seq;
                mbox->ibox.commit_log_file_offset = offset;
            }
        }
    }
    if (ret < 0 || cancel)
        mail_index_sync_rollback(&sync_ctx->sync_ctx);
    else {
        /* Set syncing_commit=TRUE so that if any sync callbacks try
           to access mails which got lost (eg. expunge callback trying
           to open the file which was just unlinked) we don't try to
           start a second index sync and crash. */
        mbox->syncing_commit = TRUE;
        if (mail_index_sync_commit(&sync_ctx->sync_ctx) < 0) {
            mail_storage_set_index_error(&mbox->ibox);
            ret = -1;
        } else {
            mbox->ibox.commit_log_file_seq = 0;
            mbox->ibox.commit_log_file_offset = 0;
        }
        mbox->syncing_commit = FALSE;
    }

    maildir_keywords_sync_deinit(sync_ctx->keywords_sync_ctx);
        sync_ctx->keywords_sync_ctx = NULL;

    i_free(sync_ctx);
    return ret;
}

int maildir_sync_index(struct maildir_index_sync_context *sync_ctx,
               bool partial)
{
    struct maildir_mailbox *mbox = sync_ctx->mbox;
    struct mail_index_view *view = sync_ctx->view;
    struct maildir_uidlist_iter_ctx *iter;
    struct mail_index_transaction *trans;
    const struct mail_index_header *hdr;
    const struct mail_index_record *rec;
    uint32_t seq, uid;
        enum maildir_uidlist_rec_flag uflags;
    const char *filename;
    enum mail_flags flags;
    ARRAY_TYPE(keyword_indexes) keywords;
    ARRAY_TYPE(keyword_indexes) idx_keywords;
    uint32_t uid_validity, next_uid;
    uint64_t value;
    int ret = 0;
    bool full_rescan = FALSE;

    i_assert(maildir_uidlist_is_locked(sync_ctx->mbox->uidlist));

    hdr = mail_index_get_header(view);
    uid_validity = maildir_uidlist_get_uid_validity(mbox->uidlist);
    if (uid_validity != hdr->uid_validity &&
        uid_validity != 0 && hdr->uid_validity != 0) {
        /* uidvalidity changed and mailbox isn't being initialized,
           reset mailbox so we can add all messages as new */
        mail_storage_set_critical(STORAGE(mbox->storage),
            "Maildir %s sync: UIDVALIDITY changed (%u -> %u)",
            mbox->path, hdr->uid_validity, uid_validity);

        mail_index_mark_corrupted(mbox->ibox.index);
        return -1;
    }

    sync_ctx->trans = trans =
        mail_index_transaction_begin(sync_ctx->view, FALSE, TRUE);

    seq = 0;
    t_array_init(&keywords, MAILDIR_MAX_KEYWORDS);
    t_array_init(&idx_keywords, MAILDIR_MAX_KEYWORDS);
    iter = maildir_uidlist_iter_init(mbox->uidlist);
    while (maildir_uidlist_iter_next(iter, &uid, &uflags, &filename)) {
        maildir_filename_get_flags(sync_ctx->keywords_sync_ctx,
                       filename, &flags, &keywords);

        /* the private flags are kept only in indexes. don't use them
           at all even for newly seen mails */
        flags &= ~mbox->private_flags_mask;

        if ((uflags & MAILDIR_UIDLIST_REC_FLAG_RECENT) != 0 &&
            (uflags & MAILDIR_UIDLIST_REC_FLAG_NEW_DIR) != 0 &&
            (uflags & MAILDIR_UIDLIST_REC_FLAG_MOVED) == 0) {
            /* mail is recent for next session as well */
            flags |= MAIL_RECENT;
        }

    __again:
        seq++;

        if (seq > hdr->messages_count) {
            if (uid < hdr->next_uid) {
                /* most likely a race condition: we read the
                   maildir, then someone else expunged messages
                   and committed changes to index. so, this
                   message shouldn't actually exist. mark it
                   racy and check in next sync.

                   the difference between this and the later
                   check is that this one happens when messages
                   are expunged from the end */
                if ((uflags &
                    MAILDIR_UIDLIST_REC_FLAG_NONSYNCED) != 0) {
                    /* partial syncing */
                    continue;
                }
                if ((uflags &
                     MAILDIR_UIDLIST_REC_FLAG_RACING) != 0) {
                    mail_storage_set_critical(
                        STORAGE(mbox->storage),
                        "Maildir %s sync: "
                        "UID < next_uid "
                        "(%u < %u, file = %s)",
                        mbox->path, uid, hdr->next_uid,
                        filename);
                    mail_index_mark_corrupted(
                        mbox->ibox.index);
                    ret = -1;
                    break;
                }
                mbox->dirty_cur_time = ioloop_time;
                maildir_uidlist_add_flags(mbox->uidlist,
                    filename,
                    MAILDIR_UIDLIST_REC_FLAG_RACING);

                seq--;
                continue;
            }

            mail_index_append(trans, uid, &seq);
            mail_index_update_flags(trans, seq, MODIFY_REPLACE,
                        flags);

            if (array_count(&keywords) > 0) {
                struct mail_keywords *kw;

                kw = mail_index_keywords_create_from_indexes(
                    trans, &keywords);
                mail_index_update_keywords(trans, seq,
                               MODIFY_REPLACE, kw);
                mail_index_keywords_free(&kw);
            }
            continue;
        }

        if (mail_index_lookup(view, seq, &rec) < 0) {
            mail_storage_set_index_error(&mbox->ibox);
            ret = -1;
            break;
        }

        if (rec->uid < uid) {
            /* expunged */
            mail_index_expunge(trans, seq);
            goto __again;
        }

        if (rec->uid > uid) {
            /* most likely a race condition: we read the
               maildir, then someone else expunged messages and
               committed changes to index. so, this message
               shouldn't actually exist. mark it racy and check
               in next sync. */
            if ((uflags &
                MAILDIR_UIDLIST_REC_FLAG_NONSYNCED) != 0) {
                /* partial syncing */
                seq--;
                continue;
            }
            if ((uflags & MAILDIR_UIDLIST_REC_FLAG_RACING) != 0) {
                mail_storage_set_critical(
                    STORAGE(mbox->storage),
                    "Maildir %s sync: "
                    "UID inserted in the middle of mailbox "
                    "(%u > %u, file = %s)",
                    mbox->path, rec->uid, uid, filename);
                mail_index_mark_corrupted(mbox->ibox.index);
                ret = -1;
                break;
            }

            mbox->dirty_cur_time = ioloop_time;
            maildir_uidlist_add_flags(mbox->uidlist, filename,
                MAILDIR_UIDLIST_REC_FLAG_RACING);

            seq--;
            continue;
        }

        /* the private flags are stored only in indexes, keep them */
        flags |= rec->flags & mbox->private_flags_mask;

        if ((rec->flags & MAIL_RECENT) != 0) {
            index_mailbox_set_recent(&mbox->ibox, seq);
            if (mbox->ibox.keep_recent) {
                flags |= MAIL_RECENT;
            } else {
                mail_index_update_flags(trans, seq,
                            MODIFY_REMOVE,
                            MAIL_RECENT);
            }
        }

        if ((uflags & MAILDIR_UIDLIST_REC_FLAG_NONSYNCED) != 0) {
            /* partial syncing */
            if ((flags & MAIL_RECENT) != 0) {
                /* we last saw this mail in new/, but it's
                   not there anymore. possibly expunged,
                   make sure. */
                full_rescan = TRUE;
            }
            continue;
        }

        if ((rec->flags & MAIL_INDEX_MAIL_FLAG_DIRTY) != 0) {
            /* we haven't been able to update maildir with this
               record's flag changes. don't sync them. */
            continue;
        }

        if (((uint8_t)flags & ~MAIL_RECENT) !=
            (rec->flags & (MAIL_FLAGS_MASK^MAIL_RECENT))) {
            /* FIXME: this is wrong if there's pending changes in
               transaction log already. it gets fixed in next sync
               however.. */
            mail_index_update_flags(trans, seq, MODIFY_REPLACE,
                        flags);
        } else if ((flags & MAIL_RECENT) == 0 &&
               (rec->flags & MAIL_RECENT) != 0) {
            /* just remove recent flag */
            mail_index_update_flags(trans, seq, MODIFY_REMOVE,
                        MAIL_RECENT);
        }

        /* update keywords if they have changed */
        if (mail_index_lookup_keywords(view, seq, &idx_keywords) < 0) {
            mail_storage_set_index_error(&mbox->ibox);
            ret = -1;
            break;
        }
        if (!index_keyword_array_cmp(&keywords, &idx_keywords)) {
            struct mail_keywords *kw;

            kw = mail_index_keywords_create_from_indexes(
                trans, &keywords);
            mail_index_update_keywords(trans, seq,
                           MODIFY_REPLACE, kw);
            mail_index_keywords_free(&kw);
        }
    }
    maildir_uidlist_iter_deinit(iter);
    array_free(&keywords);

    if (!partial) {
        /* expunge the rest */
        for (seq++; seq <= hdr->messages_count; seq++)
            mail_index_expunge(trans, seq);

        /* next_uid must be updated only in non-partial syncs since
           partial syncs don't add the new mails to index. also we'll
           have to do it here before syncing index records, since after
           that the uidlist's next_uid value may have changed. */
        next_uid = maildir_uidlist_get_next_uid(mbox->uidlist);
        if (next_uid != 0 && hdr->next_uid != next_uid) {
            mail_index_update_header(trans,
                offsetof(struct mail_index_header, next_uid),
                &next_uid, sizeof(next_uid), FALSE);
        }
    }

    if (!mbox->syncing_commit) {
        /* now, sync the index. NOTE: may recurse back to here with
           partial syncs */
        mbox->syncing_commit = TRUE;
        if (maildir_sync_index_records(sync_ctx) < 0)
            ret = -1;
        mbox->syncing_commit = FALSE;
    }

    if (mbox->dirty_cur_time != 0)
        mbox->last_dirty_flags |= MAILDIR_DIRTY_CUR;

    if (mbox->last_cur_mtime != (time_t)hdr->sync_stamp) {
        uint32_t sync_stamp = mbox->last_cur_mtime;

        mail_index_update_header(trans,
            offsetof(struct mail_index_header, sync_stamp),
            &sync_stamp, sizeof(sync_stamp), TRUE);
    }

    /* FIXME: use a header extension instead of sync_size.. */
    value = mbox->last_new_mtime |
        ((uint64_t)mbox->last_dirty_flags << 32);
    if (value != hdr->sync_size) {
        mail_index_update_header(trans,
            offsetof(struct mail_index_header, sync_size),
            &value, sizeof(value), TRUE);
    }

    if (hdr->uid_validity == 0) {
        /* get the initial uidvalidity */
        if (maildir_uidlist_update(mbox->uidlist) < 0)
            ret = -1;
        uid_validity = maildir_uidlist_get_uid_validity(mbox->uidlist);
        if (uid_validity == 0) {
            uid_validity = ioloop_time;
            maildir_uidlist_set_uid_validity(mbox->uidlist,
                             uid_validity);
        }
    } else if (uid_validity == 0) {
        maildir_uidlist_set_uid_validity(mbox->uidlist,
                         hdr->uid_validity);
    }

    if (uid_validity != hdr->uid_validity && uid_validity != 0) {
        mail_index_update_header(trans,
            offsetof(struct mail_index_header, uid_validity),
            &uid_validity, sizeof(uid_validity), TRUE);
    }

    return ret < 0 ? -1 : (full_rescan ? 0 : 1);
}

static int maildir_sync_context(struct maildir_sync_context *ctx, bool forced,
                bool sync_last_commit)
{
    bool new_changed, cur_changed, full_rescan = FALSE;
    int ret;

    if (sync_last_commit) {
        new_changed = cur_changed = FALSE;
    } else if (!forced) {
        if (maildir_sync_quick_check(ctx->mbox,
                         ctx->new_dir, ctx->cur_dir,
                         &new_changed, &cur_changed) < 0)
            return -1;

        if (!new_changed && !cur_changed)
            return 1;
    } else {
        new_changed = cur_changed = TRUE;
    }

    /*
       Locking, locking, locking.. Wasn't maildir supposed to be lockless?

       We can get here either as beginning a real maildir sync, or when
       committing changes to maildir but a file was lost (maybe renamed).

       So, we're going to need two locks. One for index and one for
       uidlist. To avoid deadlocking do the uidlist lock always first.

       uidlist is needed only for figuring out UIDs for newly seen files,
       so theoretically we wouldn't need to lock it unless there are new
       files. It has a few problems though, assuming the index lock didn't
       already protect it (eg. in-memory indexes):

       1. Just because you see a new file which doesn't exist in uidlist
       file, doesn't mean that the file really exists anymore, or that
       your readdir() lists all new files. Meaning that this is possible:

         A: opendir(), readdir() -> new file ...
         -- new files are written to the maildir --
         B: opendir(), readdir() -> new file, lock uidlist,
        readdir() -> another new file, rewrite uidlist, unlock
         A: ... lock uidlist, readdir() -> nothing left, rewrite uidlist,
        unlock

       The second time running A didn't see the two new files. To handle
       this correctly, it must not remove the new unseen files from
       uidlist. This is possible to do, but adds extra complexity.

       2. If another process is rename()ing files while we are
       readdir()ing, it's possible that readdir() never lists some files,
       causing Dovecot to assume they were expunged. In next sync they
       would show up again, but client could have already been notified of
       that and they would show up under new UIDs, so the damage is
       already done.

       Both of the problems can be avoided if we simply lock the uidlist
       before syncing and keep it until sync is finished. Typically this
       would happen in any case, as there is the index lock..

       The second case is still a problem with external changes though,
       because maildir doesn't require any kind of locking. Luckily this
       problem rarely happens except under high amount of modifications.
    */

    ctx->partial = !cur_changed;
    ret = maildir_uidlist_sync_init(ctx->mbox->uidlist, ctx->partial,
                    &ctx->uidlist_sync_ctx);
    if (ret <= 0) {
        /* failure / timeout. if forced is TRUE, we could still go
           forward and check only for renamed files, but is it worth
           the trouble? .. */
        return ret;
    }

    if (!ctx->mbox->syncing_commit) {
        if (maildir_sync_index_begin(ctx->mbox,
                         &ctx->index_sync_ctx) < 0)
            return -1;
    }

    if (new_changed || cur_changed) {
        /* if we're going to check cur/ dir our current logic requires
           that new/ dir is checked as well. it's a good idea anyway. */
        while ((ret = maildir_scan_dir(ctx, TRUE)) > 0) {
            /* rename()d at least some files, which might have
               caused some other files to be missed. check again
               (see MAILDIR_RENAME_RESCAN_COUNT). */
        }
        if (ret < 0)
            return -1;

        if (cur_changed) {
            if (maildir_scan_dir(ctx, FALSE) < 0)
                return -1;
        }

        /* finish uidlist syncing, but keep it still locked */
        maildir_uidlist_sync_finish(ctx->uidlist_sync_ctx);
    }

    if (!ctx->mbox->syncing_commit) {
        /* NOTE: index syncing here might cause a re-sync due to
           files getting lost, so this function might be called
           re-entrantly. FIXME: and that breaks in
           maildir_uidlist_sync_deinit() */
        ret = maildir_sync_index(ctx->index_sync_ctx, ctx->partial);
        if (maildir_sync_index_finish(&ctx->index_sync_ctx,
                          ret < 0, FALSE) < 0)
            return -1;

        if (ret < 0)
            return -1;
        if (ret == 0)
            full_rescan = TRUE;

        i_assert(maildir_uidlist_is_locked(ctx->mbox->uidlist));
    }

    ret = maildir_uidlist_sync_deinit(&ctx->uidlist_sync_ctx);
    return ret < 0 ? -1 : (full_rescan ? 0 : 1);
}

int maildir_storage_sync_force(struct maildir_mailbox *mbox)
{
        struct maildir_sync_context *ctx;
    int ret;

    ctx = maildir_sync_context_new(mbox);
    ret = maildir_sync_context(ctx, TRUE, FALSE);
    maildir_sync_deinit(ctx);
    return ret < 0 ? -1 : 0;
}

int maildir_sync_last_commit(struct maildir_mailbox *mbox)
{
        struct maildir_sync_context *ctx;
    int ret;

    if (mbox->ibox.commit_log_file_seq == 0)
        return 0;

    ctx = maildir_sync_context_new(mbox);
    ret = maildir_sync_context(ctx, FALSE, TRUE);
    maildir_sync_deinit(ctx);
    return ret < 0 ? -1 : 0;
}

struct mailbox_sync_context *
maildir_storage_sync_init(struct mailbox *box, enum mailbox_sync_flags flags)
{
    struct maildir_mailbox *mbox = (struct maildir_mailbox *)box;
    struct maildir_sync_context *ctx;
    int ret = 0;

    if (!box->opened)
        index_storage_mailbox_open(&mbox->ibox);

    if ((flags & MAILBOX_SYNC_FLAG_FAST) == 0 ||
        mbox->ibox.sync_last_check + MAILBOX_FULL_SYNC_INTERVAL <=
        ioloop_time) {
        mbox->ibox.sync_last_check = ioloop_time;

        ctx = maildir_sync_context_new(mbox);
        ret = maildir_sync_context(ctx, FALSE, FALSE);
        maildir_sync_deinit(ctx);

        i_assert(!maildir_uidlist_is_locked(mbox->uidlist) ||
             mbox->ibox.keep_locked);

        if (ret == 0) {
            /* lost some files from new/, see if thery're in cur/ */
            ret = maildir_storage_sync_force(mbox);
        }
    }

    return index_mailbox_sync_init(box, flags, ret < 0);
}

int maildir_sync_is_synced(struct maildir_mailbox *mbox)
{
    const char *new_dir, *cur_dir;
    bool new_changed, cur_changed;
    int ret;

    t_push();
    new_dir = t_strconcat(mbox->path, "/new", NULL);
    cur_dir = t_strconcat(mbox->path, "/cur", NULL);

    ret = maildir_sync_quick_check(mbox, new_dir, cur_dir,
                       &new_changed, &cur_changed);
    t_pop();
    return ret < 0 ? -1 : (!new_changed && !cur_changed);
}