index/maildir/maildir-sync.c

	maildir-sync.c revision 305465bb1a4c5d90c4b4e2c2790eb05fa4ebc41e
bcb4e51a409d94ae670de96afb8483a4f7855294Stephan Bosch/* Copyright (c) 2004-2009 Dovecot authors, see the included COPYING file */
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen/*
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   Here's a description of how we handle Maildir synchronization and
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   it's problems:
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   We want to be as efficient as we can. The most efficient way to
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   check if changes have occurred is to stat() the new/ and cur/
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   directories and uidlist file - if their mtimes haven't changed,
c68f28e2cf5f9621511bece0414335e551dc82c6Timo Sirainen   there's no changes and we don't need to do anything.
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   Problem 1: Multiple changes can happen within a single second -
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   nothing guarantees that once we synced it, someone else didn't just
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   then make a modification. Such modifications wouldn't get noticed
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   until a new modification occurred later.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen   Problem 2: Syncing cur/ directory is much more costly than syncing
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   new/. Moving mails from new/ to cur/ will always change mtime of
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   cur/ causing us to sync it as well.
e42e27fcc497c7b4a5cc0b6ff304abca5ccfcb4fTimo Sirainen
e42e27fcc497c7b4a5cc0b6ff304abca5ccfcb4fTimo Sirainen   Problem 3: We may not be able to move mail from new/ to cur/
e42e27fcc497c7b4a5cc0b6ff304abca5ccfcb4fTimo Sirainen   because we're out of quota, or simply because we're accessing a
e42e27fcc497c7b4a5cc0b6ff304abca5ccfcb4fTimo Sirainen   read-only mailbox.
e42e27fcc497c7b4a5cc0b6ff304abca5ccfcb4fTimo Sirainen
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   MAILDIR_SYNC_SECS
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   -----------------
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   Several checks below use MAILDIR_SYNC_SECS, which should be maximum
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen   clock drift between all computers accessing the maildir (eg. via
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   NFS), rounded up to next second. Our default is 1 second, since
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen   everyone should be using NTP.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen   Note that setting it to 0 works only if there's only one computer
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   accessing the maildir. It's practically impossible to make two
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   clocks _exactly_ synchronized.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   It might be possible to only use file server's clock by looking at
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   the atime field, but I don't know how well that would actually work.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen   cur directory
804fa3f03bd9170272168a5ad214053bbe3160c7Josef 'Jeff' Sipek   -------------
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   We have dirty_cur_time variable which is set to cur/ directory's
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   mtime when it's >= time() - MAILDIR_SYNC_SECS and we _think_ we have
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   synchronized the directory.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
7631f16156aca373004953fe6b01a7f343fb47e0Timo Sirainen   When dirty_cur_time is non-zero, we don't synchronize the cur/
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   directory until
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen      a) cur/'s mtime changes
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen      b) opening a mail fails with ENOENT
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen      c) time() > dirty_cur_time + MAILDIR_SYNC_SECS
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
efe78d3ba24fc866af1c79b9223dc0809ba26cadStephan Bosch   This allows us to modify the maildir multiple times without having
e6440616c02bb1404dc35debf45d9741260c7831Timo Sirainen   to sync it at every change. The sync will eventually be done to
e6440616c02bb1404dc35debf45d9741260c7831Timo Sirainen   make sure we didn't miss any external changes.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
d4002fe1f64d25a792f76fb102ef7dc519cd4e24Martti Rannanjärvi   The dirty_cur_time is set when:
d4002fe1f64d25a792f76fb102ef7dc519cd4e24Martti Rannanjärvi
d4002fe1f64d25a792f76fb102ef7dc519cd4e24Martti Rannanjärvi      - we change message flags
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen      - we expunge messages
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen      - we move mail from new/ to cur/
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen      - we sync cur/ directory and it's mtime is >= time() - MAILDIR_SYNC_SECS
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen   It's unset when we do the final syncing, ie. when mtime is
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen   older than time() - MAILDIR_SYNC_SECS.
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   new directory
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   -------------
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   If new/'s mtime is >= time() - MAILDIR_SYNC_SECS, always synchronize
804fa3f03bd9170272168a5ad214053bbe3160c7Josef 'Jeff' Sipek   it. dirty_cur_time-like feature might save us a few syncs, but
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   that might break a client which saves a mail in one connection and
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   tries to fetch it in another one. new/ directory is almost always
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   empty, so syncing it should be very fast anyway. Actually this can
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   still happen if we sync only new/ dir while another client is also
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen   moving mails from it to cur/ - it takes us a while to see them.
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen   That's pretty unlikely to happen however, and only way to fix it
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen   would be to always synchronize cur/ after new/.
c68f28e2cf5f9621511bece0414335e551dc82c6Timo Sirainen
c68f28e2cf5f9621511bece0414335e551dc82c6Timo Sirainen   Normally we move all mails from new/ to cur/ whenever we sync it. If
c68f28e2cf5f9621511bece0414335e551dc82c6Timo Sirainen   it's not possible for some reason, we mark the mail with "probably
c68f28e2cf5f9621511bece0414335e551dc82c6Timo Sirainen   exists in new/ directory" flag.
c68f28e2cf5f9621511bece0414335e551dc82c6Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   If rename() still fails because of ENOSPC or EDQUOT, we still save
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   the flag changes in index with dirty-flag on. When moving the mail
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   to cur/ directory, or when we notice it's already moved there, we
e6440616c02bb1404dc35debf45d9741260c7831Timo Sirainen   apply the flag changes to the filename, rename it and remove the
e6440616c02bb1404dc35debf45d9741260c7831Timo Sirainen   dirty flag. If there's dirty flags, this should be tried every time
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen   after expunge or when closing the mailbox.
e6440616c02bb1404dc35debf45d9741260c7831Timo Sirainen
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen   uidlist
e6440616c02bb1404dc35debf45d9741260c7831Timo Sirainen   -------
48325adac125d7ff275ec69b05b7a92be9637630Timo Sirainen
48325adac125d7ff275ec69b05b7a92be9637630Timo Sirainen   This file contains UID <-> filename mappings. It's updated only when
1b6c4fdd2bb4234b5711874b3845547f49649744Timo Sirainen   new mail arrives, so it may contain filenames that have already been
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen   deleted. Updating is done by getting uidlist.lock file, writing the
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen   whole uidlist into it and rename()ing it over the old uidlist. This
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen   means there's no need to lock the file for reading.
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen   Whenever uidlist is rewritten, it's mtime must be larger than the old
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen   one's. Use utime() before rename() if needed. Note that inode checking
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen   wouldn't have been sufficient as inode numbers can be reused.
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen   This file is usually read the first time you need to know filename for
d1ba8ecbb936ace90179d2292952546708d68f71Timo Sirainen   given UID. After that it's not re-read unless new mails come that we
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen   don't know about.
ad9afb64630511d5e25bc5bc11c5304986156928Timo Sirainen
d4002fe1f64d25a792f76fb102ef7dc519cd4e24Martti Rannanjärvi   broken clients
d4002fe1f64d25a792f76fb102ef7dc519cd4e24Martti Rannanjärvi   --------------
d4002fe1f64d25a792f76fb102ef7dc519cd4e24Martti Rannanjärvi
d4002fe1f64d25a792f76fb102ef7dc519cd4e24Martti Rannanjärvi   Originally the middle identifier in Maildir filename was specified
efb83f10b2a557d7427c311da52d768fb91e1b47Timo Sirainen   only as <process id>_<delivery counter>. That however created a
efb83f10b2a557d7427c311da52d768fb91e1b47Timo Sirainen   problem with randomized PIDs which made it possible that the same
c25dfa96bc32e8841c9a8cf5ba02fffba4290160Timo Sirainen   PID was reused within one second.
3177b410680f3915549719f84a4acbffd4f9c561Timo Sirainen
3177b410680f3915549719f84a4acbffd4f9c561Timo Sirainen   So if within one second a mail was delivered, MUA moved it to cur/
3177b410680f3915549719f84a4acbffd4f9c561Timo Sirainen   and another mail was delivered by a new process using same PID as
c3d9da3955043aef88c17b71f2081e894186aa6bTimo Sirainen   the first one, we likely ended up overwriting the first mail when
c3d9da3955043aef88c17b71f2081e894186aa6bTimo Sirainen   the second mail was moved over it.
c25dfa96bc32e8841c9a8cf5ba02fffba4290160Timo Sirainen
c25dfa96bc32e8841c9a8cf5ba02fffba4290160Timo Sirainen   Nowadays everyone should be giving a bit more specific identifier,
e6440616c02bb1404dc35debf45d9741260c7831Timo Sirainen   for example include microseconds in it which Dovecot does.
e6440616c02bb1404dc35debf45d9741260c7831Timo Sirainen
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen   There's a simple way to prevent this from happening in some cases:
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen   Don't move the mail from new/ to cur/ if it's mtime is >= time() -
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   MAILDIR_SYNC_SECS. The second delivery's link() call then fails
de62ce819d59a529530da4b57be1b8d6dad13d6bTimo Sirainen   because the file is already in new/, and it will then use a
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   different filename. There's a few problems with this however:
804fa3f03bd9170272168a5ad214053bbe3160c7Josef 'Jeff' Sipek
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen      - it requires extra stat() call which is unneeded extra I/O
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen      - another MUA might still move the mail to cur/
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen      - if first file's flags are modified by either Dovecot or another
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen        MUA, it's moved to cur/ (you _could_ just do the dirty-flagging
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen    but that'd be ugly)
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
efe78d3ba24fc866af1c79b9223dc0809ba26cadStephan Bosch   Because this is useful only for very few people and it requires
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   extra I/O, I decided not to implement this. It should be however
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   quite easy to do since we need to be able to deal with files in new/
e2a88d59c0d47d63ce1ad5b1fd95e487124a3fd4Timo Sirainen   in any case.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   It's also possible to never accidentally overwrite a mail by using
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen   link() + unlink() rather than rename(). This however isn't very
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen   good idea as it introduces potential race conditions when multiple
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen   clients are accessing the mailbox:
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen   Trying to move the same mail from new/ to cur/ at the same time:
b58aafbd21b365117538f73f306d22f75acd91f1Timo Sirainen
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen      a) Client 1 uses slightly different filename than client 2,
b58aafbd21b365117538f73f306d22f75acd91f1Timo Sirainen         for example one sets read-flag on but the other doesn't.
f89eb8f2cda0bd6d40a9f96db1c92517f0593871Martti Rannanjärvi     You have the same mail duplicated now.
f89eb8f2cda0bd6d40a9f96db1c92517f0593871Martti Rannanjärvi
1f19649986397419d014febd1337c6eb7b530f26Timo Sirainen      b) Client 3 sees the mail between Client 1's and 2's link() calls
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen         and changes it's flag. You have the same mail duplicated now.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   And it gets worse when they're unlink()ing in cur/ directory:
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen      c) Client 1 changes mails's flag and client 2 changes it back
a8bc64d2ec8babb5109fa23aa3c90383de61cd69Timo Sirainen         between 1's link() and unlink(). The mail is now expunged.
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen      d) If you try to deal with the duplicates by unlink()ing another
2b9dbb270ad82e58d5f3581436e6f143176d5819Timo Sirainen         one of them, you might end up unlinking both of them.
2b9dbb270ad82e58d5f3581436e6f143176d5819Timo Sirainen
a8bc64d2ec8babb5109fa23aa3c90383de61cd69Timo Sirainen   So, what should we do then if we notice a duplicate? First of all,
147a788fea2a88f7125b27226451271d55cf5b01Timo Sirainen   it might not be a duplicate at all, readdir() might have just
147a788fea2a88f7125b27226451271d55cf5b01Timo Sirainen   returned it twice because it was just renamed. What we should do is
147a788fea2a88f7125b27226451271d55cf5b01Timo Sirainen   create a completely new base name for it and rename() it to that.
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen   If the call fails with ENOENT, it only means that it wasn't a
2b9dbb270ad82e58d5f3581436e6f143176d5819Timo Sirainen   duplicate after all.
2b9dbb270ad82e58d5f3581436e6f143176d5819Timo Sirainen*/
147a788fea2a88f7125b27226451271d55cf5b01Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "lib.h"
99695d99930b35c2bac85d52e976b44cf8485d83Timo Sirainen#include "ioloop.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "array.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "buffer.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "hash.h"
de62ce819d59a529530da4b57be1b8d6dad13d6bTimo Sirainen#include "str.h"
de62ce819d59a529530da4b57be1b8d6dad13d6bTimo Sirainen#include "eacces-error.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "nfs-workarounds.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "maildir-storage.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "maildir-uidlist.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "maildir-filename.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include "maildir-sync.h"
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include <stdio.h>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include <stddef.h>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include <stdlib.h>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include <unistd.h>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include <dirent.h>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen#include <sys/stat.h>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen#define MAILDIR_FILENAME_FLAG_FOUND 128
b9f564d00b7a115f465ffd6840341c7b8f9bfc8aTimo Sirainen
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen/* When rename()ing many files from new/ to cur/, it's possible that next
e2a88d59c0d47d63ce1ad5b1fd95e487124a3fd4Timo Sirainen   readdir() skips some files. we don't of course wish to lose them, so we
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen   go and rescan the new/ directory again from beginning until no files are
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen   left. This value is just an optimization to avoid checking the directory
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen   twice unneededly. usually only NFS is the problem case. 1 is the safest
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen   bet here, but I guess 5 will do just fine too. */
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen#define MAILDIR_RENAME_RESCAN_COUNT 5
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen/* This is mostly to avoid infinite looping when rename() destination already
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen   exists as the hard link of the file itself. */
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen#define MAILDIR_SCAN_DIR_MAX_COUNT 5
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen#define DUPE_LINKS_DELETE_SECS 30
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainenstruct maildir_sync_context {
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen        struct maildir_mailbox *mbox;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen    const char *new_dir, *cur_dir;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen    enum mailbox_sync_flags flags;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen    time_t last_touch, last_notify;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen    struct maildir_uidlist_sync_ctx *uidlist_sync_ctx;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen    struct maildir_index_sync_context *index_sync_ctx;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen    unsigned int partial:1;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen    unsigned int locked:1;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen};
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainenvoid maildir_sync_notify(struct maildir_sync_context *ctx)
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen{
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen    time_t now;
9865d9e7c5713e41db939222ed9c0225a11fb99eTimo Sirainen
    if (ctx == NULL) {
        /* we got here from maildir-save.c. it has no
           maildir_sync_context,  */
        return;
    }

    now = time(NULL);
    if (now - ctx->last_touch > MAILDIR_LOCK_TOUCH_SECS && ctx->locked) {
        (void)maildir_uidlist_lock_touch(ctx->mbox->uidlist);
        ctx->last_touch = now;
    }
    if (now - ctx->last_notify > MAIL_STORAGE_STAYALIVE_SECS) {
        struct mailbox *box = &ctx->mbox->ibox.box;

        if (box->storage->callbacks->notify_ok != NULL) {
            box->storage->callbacks->
                notify_ok(box, "Hang in there..",
                      box->storage->callback_context);
        }
        ctx->last_notify = now;
    }
}

static struct maildir_sync_context *
maildir_sync_context_new(struct maildir_mailbox *mbox,
             enum mailbox_sync_flags flags)
{
        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);
    ctx->last_touch = ioloop_time;
    ctx->last_notify = ioloop_time;
    ctx->flags = flags;
    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 *fname2)
{
    const char *fname1, *path1, *path2;
    const char *new_fname, *new_path;
    struct stat st1, st2;

    fname1 = maildir_uidlist_sync_get_full_filename(ctx->uidlist_sync_ctx,
                            fname2);
    i_assert(fname1 != NULL);

    path1 = t_strconcat(dir, "/", fname1, NULL);
    path2 = t_strconcat(dir, "/", fname2, NULL);

    if (stat(path1, &st1) < 0 || stat(path2, &st2) < 0) {
        /* most likely the files just don't exist anymore.
           don't really care about other errors much. */
        return 0;
    }
    if (st1.st_ino == st2.st_ino &&
        CMP_DEV_T(st1.st_dev, st2.st_dev)) {
        /* Files are the same. this means either a race condition
           between stat() calls, or that the files were link()ed. */
        if (st1.st_nlink > 1 && st2.st_nlink == st1.st_nlink &&
            st1.st_ctime == st2.st_ctime &&
            st1.st_ctime < ioloop_time - DUPE_LINKS_DELETE_SECS) {
            /* The file has hard links and it hasn't had any
               changes (such as renames) for a while, so this
               isn't a race condition.

               rename()ing one file on top of the other would fix
               this safely, except POSIX decided that rename()
               doesn't work that way. So we'll have unlink() one
               and hope that another process didn't just decide to
               unlink() the other (uidlist lock prevents this from
               happening) */
            if (unlink(path2) == 0)
                i_warning("Unlinked a duplicate: %s", path2);
            else {
                mail_storage_set_critical(
                    &ctx->mbox->storage->storage,
                    "unlink(%s) failed: %m", path2);
            }
        }
        return 0;
    }

    new_fname = maildir_filename_generate();
    new_path = t_strconcat(ctx->mbox->path, "/new/", new_fname, NULL);

    if (rename(path2, new_path) == 0)
        i_warning("Fixed a duplicate: %s -> %s", path2, new_fname);
    else if (errno != ENOENT) {
        mail_storage_set_critical(&ctx->mbox->storage->storage,
            "Couldn't fix a duplicate: rename(%s, %s) failed: %m",
            path2, new_path);
        return -1;
    }
    return 0;
}

static int
maildir_stat(struct maildir_mailbox *mbox, const char *path, struct stat *st_r)
{
    int i;

    for (i = 0;; i++) {
        if (nfs_safe_stat(path, st_r) == 0)
            return 0;
        if (errno != ENOENT || i == MAILDIR_DELETE_RETRY_COUNT)
            break;

        if (!maildir_set_deleted(mbox))
            return -1;
        /* try again */
    }

    mail_storage_set_critical(mbox->ibox.box.storage,
                  "stat(%s) failed: %m", path);
    return -1;
}

static int maildir_scan_dir(struct maildir_sync_context *ctx, bool new_dir)
{
    struct mail_storage *storage = &ctx->mbox->storage->storage;
    const char *path;
    DIR *dirp;
    string_t *src, *dest;
    struct dirent *dp;
    struct stat st;
    enum maildir_uidlist_rec_flag flags;
    unsigned int i = 0, move_count = 0;
    time_t now;
    int ret = 1;
    bool move_new, check_touch, dir_changed = FALSE;

    path = new_dir ? ctx->new_dir : ctx->cur_dir;
    for (i = 0;; i++) {
        dirp = opendir(path);
        if (dirp != NULL)
            break;

        if (errno != ENOENT || i == MAILDIR_DELETE_RETRY_COUNT) {
            if (errno == EACCES) {
                mail_storage_set_critical(storage, "%s",
                    eacces_error_get("opendir", path));
            } else {
                mail_storage_set_critical(storage,
                    "opendir(%s) failed: %m", path);
            }
            return -1;
        }

        if (!maildir_set_deleted(ctx->mbox))
            return -1;
        /* try again */
    }

#ifdef HAVE_DIRFD
    if (fstat(dirfd(dirp), &st) < 0) {
        mail_storage_set_critical(storage,
            "fstat(%s) failed: %m", path);
        (void)closedir(dirp);
        return -1;
    }
#else
    if (maildir_stat(ctx->mbox, path, &st) < 0) {
        (void)closedir(dirp);
        return -1;
    }
#endif

    now = time(NULL);
    if (new_dir) {
        ctx->mbox->maildir_hdr.new_check_time = now;
        ctx->mbox->maildir_hdr.new_mtime = st.st_mtime;
        ctx->mbox->maildir_hdr.new_mtime_nsecs = ST_MTIME_NSEC(st);
    } else {
        ctx->mbox->maildir_hdr.cur_check_time = now;
        ctx->mbox->maildir_hdr.cur_mtime = st.st_mtime;
        ctx->mbox->maildir_hdr.cur_mtime_nsecs = ST_MTIME_NSEC(st);
    }

    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 && ctx->locked;

    errno = 0;
    for (; (dp = readdir(dirp)) != NULL; errno = 0) {
        if (dp->d_name[0] == '.')
            continue;

        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 */
                dir_changed = TRUE;
                move_count++;
                flags |= MAILDIR_UIDLIST_REC_FLAG_MOVED |
                    MAILDIR_UIDLIST_REC_FLAG_RECENT;
            } else if (ENOTFOUND(errno)) {
                /* someone else moved it already */
                dir_changed = TRUE;
                move_count++;
                flags |= MAILDIR_UIDLIST_REC_FLAG_MOVED |
                    MAILDIR_UIDLIST_REC_FLAG_RECENT;
            } else if (ENOSPACE(errno) || errno == EACCES) {
                /* not enough disk space / read-only maildir,
                   leave here */
                flags |= MAILDIR_UIDLIST_REC_FLAG_NEW_DIR;
                move_new = FALSE;
            } else {
                flags |= MAILDIR_UIDLIST_REC_FLAG_NEW_DIR;
                mail_storage_set_critical(storage,
                    "rename(%s, %s) failed: %m",
                    str_c(src), str_c(dest));
            }
            if ((move_count % MAILDIR_SLOW_MOVE_COUNT) == 0)
                maildir_sync_notify(ctx);
        } else if (new_dir) {
            flags |= MAILDIR_UIDLIST_REC_FLAG_NEW_DIR |
                MAILDIR_UIDLIST_REC_FLAG_RECENT;
        }

        i++;
        if ((i % MAILDIR_SLOW_CHECK_COUNT) == 0)
            maildir_sync_notify(ctx);

        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 */
            T_BEGIN {
                ret = maildir_fix_duplicate(ctx, path,
                                dp->d_name);
            } T_END;
            if (ret < 0)
                break;
        }
    }

    if (errno != 0) {
        mail_storage_set_critical(storage,
                      "readdir(%s) failed: %m", path);
        ret = -1;
    }

    if (closedir(dirp) < 0) {
        mail_storage_set_critical(storage,
                      "closedir(%s) failed: %m", path);
        ret = -1;
    }

    if (dir_changed) {
        /* save the exact new times. the new mtimes should be >=
           "now", but just in case something weird happens and mtime
           doesn't update, use "now". */
        if (stat(ctx->new_dir, &st) == 0) {
            ctx->mbox->maildir_hdr.new_check_time =
                I_MAX(st.st_mtime, now);
            ctx->mbox->maildir_hdr.new_mtime = st.st_mtime;
            ctx->mbox->maildir_hdr.new_mtime_nsecs =
                ST_MTIME_NSEC(st);
        }
        if (stat(ctx->cur_dir, &st) == 0) {
            ctx->mbox->maildir_hdr.new_check_time =
                I_MAX(st.st_mtime, now);
            ctx->mbox->maildir_hdr.cur_mtime = st.st_mtime;
            ctx->mbox->maildir_hdr.cur_mtime_nsecs =
                ST_MTIME_NSEC(st);
        }
    }

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

int maildir_sync_header_refresh(struct maildir_mailbox *mbox)
{
    const void *data;
    size_t data_size;

    if (mail_index_refresh(mbox->ibox.index) < 0) {
        mail_storage_set_index_error(&mbox->ibox);
        return -1;
    }

    mail_index_get_header_ext(mbox->ibox.view, mbox->maildir_ext_id,
                  &data, &data_size);
    if (data_size == 0) {
        /* doesn't exist */
        return 0;
    }

    memcpy(&mbox->maildir_hdr, data,
           I_MIN(sizeof(mbox->maildir_hdr), data_size));
    return 0;
}

static int maildir_sync_quick_check(struct maildir_mailbox *mbox, bool undirty,
                    const char *new_dir, const char *cur_dir,
                    bool *new_changed_r, bool *cur_changed_r)
{
#define DIR_DELAYED_REFRESH(hdr, name) \
    ((hdr)->name ## _check_time <= \
        (hdr)->name ## _mtime + MAILDIR_SYNC_SECS && \
     (undirty || \
      (time_t)(hdr)->name ## _check_time < ioloop_time - MAILDIR_SYNC_SECS))

#define DIR_MTIME_CHANGED(st, hdr, name) \
    ((st).st_mtime != (time_t)(hdr)->name ## _mtime || \
     !ST_NTIMES_EQUAL(ST_MTIME_NSEC(st), (hdr)->name ## _mtime_nsecs))

    struct maildir_index_header *hdr = &mbox->maildir_hdr;
    struct stat new_st, cur_st;
    bool refreshed = FALSE, check_new = FALSE, check_cur = FALSE;

    if (mbox->maildir_hdr.new_mtime == 0) {
        if (maildir_sync_header_refresh(mbox) < 0)
            return -1;
        if (mbox->maildir_hdr.new_mtime == 0) {
            /* first sync */
            *new_changed_r = *cur_changed_r = TRUE;
            return 0;
        }
    }

    *new_changed_r = *cur_changed_r = FALSE;

    /* try to avoid stat()ing by first checking delayed changes */
    if (DIR_DELAYED_REFRESH(hdr, new) ||
        (DIR_DELAYED_REFRESH(hdr, cur) &&
         !mbox->storage->set->maildir_very_dirty_syncs)) {
        /* refresh index and try again */
        if (maildir_sync_header_refresh(mbox) < 0)
            return -1;
        refreshed = TRUE;

        if (DIR_DELAYED_REFRESH(hdr, new))
            *new_changed_r = TRUE;
        if (DIR_DELAYED_REFRESH(hdr, cur) &&
            !mbox->storage->set->maildir_very_dirty_syncs)
            *cur_changed_r = TRUE;
        if (*new_changed_r && *cur_changed_r)
            return 0;
    }

    if (!*new_changed_r) {
        if (maildir_stat(mbox, new_dir, &new_st) < 0)
            return -1;
        check_new = TRUE;
    }
    if (!*cur_changed_r) {
        if (maildir_stat(mbox, cur_dir, &cur_st) < 0)
            return -1;
        check_cur = TRUE;
    }

    for (;;) {
        if (check_new)
            *new_changed_r = DIR_MTIME_CHANGED(new_st, hdr, new);
        if (check_cur)
            *cur_changed_r = DIR_MTIME_CHANGED(cur_st, hdr, cur);

        if ((!*new_changed_r && !*cur_changed_r) || refreshed)
            break;

        /* refresh index and try again */
        if (maildir_sync_header_refresh(mbox) < 0)
            return -1;
        refreshed = TRUE;
    }

    return 0;
}

static void maildir_sync_update_next_uid(struct maildir_mailbox *mbox)
{
    const struct mail_index_header *hdr;
    uint32_t uid_validity, next_uid;

    hdr = mail_index_get_header(mbox->ibox.view);
    if (hdr->uid_validity == 0)
        return;

    uid_validity = maildir_uidlist_get_uid_validity(mbox->uidlist);
    next_uid = maildir_uidlist_get_next_uid(mbox->uidlist);

    if (uid_validity == hdr->uid_validity || uid_validity == 0) {
        /* make sure uidlist's next_uid is at least as large as
           index file's. typically this happens only if uidlist gets
           deleted. */
        maildir_uidlist_set_uid_validity(mbox->uidlist,
                         hdr->uid_validity);
        maildir_uidlist_set_next_uid(mbox->uidlist,
                         hdr->next_uid, FALSE);
    }
}

static bool move_recent_messages(struct maildir_sync_context *ctx)
{
    const struct mail_index_header *hdr;

    if (ctx->mbox->ibox.keep_recent)
        return FALSE;

    (void)maildir_uidlist_refresh(ctx->mbox->uidlist);

    /* if there are files in new/, we'll need to move them. we'll check
       this by checking if we have any recent messages */
    hdr = mail_index_get_header(ctx->mbox->ibox.view);
    return hdr->first_recent_uid <
        maildir_uidlist_get_next_uid(ctx->mbox->uidlist);
}

static int maildir_sync_get_changes(struct maildir_sync_context *ctx,
                    bool *new_changed_r, bool *cur_changed_r)
{
    enum mail_index_sync_flags flags = 0;
    bool undirty = (ctx->flags & MAILBOX_SYNC_FLAG_FULL_READ) != 0;

    if (maildir_sync_quick_check(ctx->mbox, undirty,
                     ctx->new_dir, ctx->cur_dir,
                     new_changed_r, cur_changed_r) < 0)
        return -1;

    if (*new_changed_r || *cur_changed_r)
        return 1;

    if (move_recent_messages(ctx)) {
        *new_changed_r = TRUE;
        return 1;
    }

    if (!ctx->mbox->ibox.keep_recent)
        flags |= MAIL_INDEX_SYNC_FLAG_DROP_RECENT;

    return mail_index_sync_have_any(ctx->mbox->ibox.index, flags) ? 1 : 0;
}

static int maildir_sync_context(struct maildir_sync_context *ctx, bool forced,
                uint32_t *find_uid, bool *lost_files_r)
{
    enum maildir_uidlist_sync_flags sync_flags;
    enum maildir_uidlist_rec_flag flags;
    bool new_changed, cur_changed, lock_failure;
    int ret;

    *lost_files_r = FALSE;

    if (forced)
        new_changed = cur_changed = TRUE;
    else {
        ret = maildir_sync_get_changes(ctx, &new_changed, &cur_changed);
        if (ret <= 0)
            return ret;
    }

    /*
       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.
    */

    if (!cur_changed) {
        ctx->partial = TRUE;
        sync_flags = MAILDIR_UIDLIST_SYNC_PARTIAL;
    } else {
        ctx->partial = FALSE;
        sync_flags = 0;
        if (forced)
            sync_flags |= MAILDIR_UIDLIST_SYNC_FORCE;
        if ((ctx->flags & MAILBOX_SYNC_FLAG_FAST) != 0)
            sync_flags |= MAILDIR_UIDLIST_SYNC_TRYLOCK;
    }
    ret = maildir_uidlist_sync_init(ctx->mbox->uidlist, sync_flags,
                    &ctx->uidlist_sync_ctx);
    lock_failure = ret <= 0;
    if (ret <= 0) {
        struct mail_storage *storage = ctx->mbox->ibox.box.storage;

        if (ret == 0) {
            /* timeout */
            return 0;
        }
        /* locking failed. sync anyway without locking so that it's
           possible to expunge messages when out of quota. */
        if (forced) {
            /* we're already forcing a sync, we're trying to find
               a message that was probably already expunged, don't
               loop for a long time trying to find it. */
            return -1;
        }
        ret = maildir_uidlist_sync_init(ctx->mbox->uidlist, sync_flags |
                        MAILDIR_UIDLIST_SYNC_NOLOCK,
                        &ctx->uidlist_sync_ctx);
        if (ret <= 0) {
            i_assert(ret != 0);
            return -1;
        }

        if (storage->callbacks->notify_no != NULL) {
            storage->callbacks->notify_no(&ctx->mbox->ibox.box,
                "Internal mailbox synchronization failure, "
                "showing only old mails.",
                storage->callback_context);
        }
    }
    ctx->locked = maildir_uidlist_is_locked(ctx->mbox->uidlist);
    if (!ctx->locked)
        ctx->partial = TRUE;

    if (!ctx->mbox->syncing_commit && (ctx->locked || lock_failure)) {
        if (maildir_sync_index_begin(ctx->mbox, ctx,
                         &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. */
        unsigned int count = 0;

        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 (++count > MAILDIR_SCAN_DIR_MAX_COUNT)
                break;
        }
        if (ret < 0)
            return -1;

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

        maildir_sync_update_next_uid(ctx->mbox);

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

    if (!ctx->locked) {
        /* make sure we sync the maildir later */
        ctx->mbox->maildir_hdr.new_mtime = 0;
        ctx->mbox->maildir_hdr.cur_mtime = 0;
    }

    if (ctx->index_sync_ctx != NULL) {
        /* NOTE: index syncing here might cause a re-sync due to
           files getting lost, so this function might be called
           re-entrantly. */
        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)
            *lost_files_r = TRUE;

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

    if (find_uid != NULL && *find_uid != 0) {
        if (maildir_uidlist_lookup_nosync(ctx->mbox->uidlist, *find_uid,
                          &flags) == NULL) {
            /* UID is expunged */
            *find_uid = 0;
        } else if ((flags & MAILDIR_UIDLIST_REC_FLAG_NONSYNCED) == 0) {
            /* we didn't find it, possibly expunged? */
            *find_uid = 0;
        }
    }

    return maildir_uidlist_sync_deinit(&ctx->uidlist_sync_ctx);
}

int maildir_storage_sync_force(struct maildir_mailbox *mbox, uint32_t uid)
{
        struct maildir_sync_context *ctx;
    bool lost_files;
    int ret;

    T_BEGIN {
        ctx = maildir_sync_context_new(mbox, MAILBOX_SYNC_FLAG_FAST);
        ret = maildir_sync_context(ctx, TRUE, &uid, &lost_files);
        maildir_sync_deinit(ctx);
    } T_END;

    if (uid != 0) {
        /* maybe it's expunged. check again. */
        T_BEGIN {
            ctx = maildir_sync_context_new(mbox, 0);
            ret = maildir_sync_context(ctx, TRUE, NULL,
                           &lost_files);
            maildir_sync_deinit(ctx);
        } T_END;
    }
    return ret;
}

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;
    bool lost_files, force_resync;
    int ret = 0;

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

    force_resync = (flags & MAILBOX_SYNC_FLAG_FORCE_RESYNC) != 0;
    if (index_mailbox_want_full_sync(&mbox->ibox, flags)) {
        T_BEGIN {
            ctx = maildir_sync_context_new(mbox, flags);
            ret = maildir_sync_context(ctx, force_resync, NULL,
                           &lost_files);
            maildir_sync_deinit(ctx);
        } T_END;

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

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

    if (mbox->storage->set->maildir_very_dirty_syncs) {
        struct mail_index_view_sync_ctx *sync_ctx;
        bool b;

        if (mbox->flags_view == NULL) {
            mbox->flags_view =
                mail_index_view_open(mbox->ibox.index);
        }
        sync_ctx = mail_index_view_sync_begin(mbox->flags_view,
                MAIL_INDEX_VIEW_SYNC_FLAG_FIX_INCONSISTENT);
        if (mail_index_view_sync_commit(&sync_ctx, &b) < 0) {
            mail_storage_set_index_error(&mbox->ibox);
            ret = -1;
        }
        /* make sure the map stays in private memory */
        if (mbox->flags_view->map->refcount > 1) {
            struct mail_index_map *map;

            map = mail_index_map_clone(mbox->flags_view->map);
            mail_index_unmap(&mbox->flags_view->map);
            mbox->flags_view->map = map;
        }
        mail_index_record_map_move_to_private(mbox->flags_view->map);
        mail_index_map_move_to_memory(mbox->flags_view->map);
        maildir_uidlist_set_all_nonsynced(mbox->uidlist);
    }
    return index_mailbox_sync_init(box, flags, ret < 0);
}

int maildir_sync_is_synced(struct maildir_mailbox *mbox)
{
    bool new_changed, cur_changed;
    int ret;

    T_BEGIN {
        const char *new_dir, *cur_dir;

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

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