index/maildir/maildir-sync.c

	maildir-sync.c revision 43955c82f9f52c969c777b3da00bc170183dfdf2
2454dfa32c93c20a8522c6ed42fe057baaac9f9aStephan Bosch/* Copyright (c) 2004-2010 Dovecot authors, see the included COPYING file */
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen/*
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   Here's a description of how we handle Maildir synchronization and
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   it's problems:
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   We want to be as efficient as we can. The most efficient way to
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen   check if changes have occurred is to stat() the new/ and cur/
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen   directories and uidlist file - if their mtimes haven't changed,
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   there's no changes and we don't need to do anything.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   Problem 1: Multiple changes can happen within a single second -
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   nothing guarantees that once we synced it, someone else didn't just
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   then make a modification. Such modifications wouldn't get noticed
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   until a new modification occurred later.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen   Problem 2: Syncing cur/ directory is much more costly than syncing
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   new/. Moving mails from new/ to cur/ will always change mtime of
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   cur/ causing us to sync it as well.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   Problem 3: We may not be able to move mail from new/ to cur/
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   because we're out of quota, or simply because we're accessing a
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   read-only mailbox.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   MAILDIR_SYNC_SECS
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   -----------------
4e8e7a93628b4ed60aaaa47c6f72c1433f21e81dTimo Sirainen
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi   Several checks below use MAILDIR_SYNC_SECS, which should be maximum
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi   clock drift between all computers accessing the maildir (eg. via
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   NFS), rounded up to next second. Our default is 1 second, since
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi   everyone should be using NTP.
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   Note that setting it to 0 works only if there's only one computer
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   accessing the maildir. It's practically impossible to make two
b7324e421e2132cbbf753e6fdbe675bbaecdf929Timo Sirainen   clocks _exactly_ synchronized.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   It might be possible to only use file server's clock by looking at
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   the atime field, but I don't know how well that would actually work.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   cur directory
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   -------------
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   We have dirty_cur_time variable which is set to cur/ directory's
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   mtime when it's >= time() - MAILDIR_SYNC_SECS and we _think_ we have
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   synchronized the directory.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen   When dirty_cur_time is non-zero, we don't synchronize the cur/
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen   directory until
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen      a) cur/'s mtime changes
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen      b) opening a mail fails with ENOENT
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen      c) time() > dirty_cur_time + MAILDIR_SYNC_SECS
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   This allows us to modify the maildir multiple times without having
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   to sync it at every change. The sync will eventually be done to
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   make sure we didn't miss any external changes.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   The dirty_cur_time is set when:
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen      - we change message flags
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen      - we expunge messages
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen      - we move mail from new/ to cur/
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen      - we sync cur/ directory and it's mtime is >= time() - MAILDIR_SYNC_SECS
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   It's unset when we do the final syncing, ie. when mtime is
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   older than time() - MAILDIR_SYNC_SECS.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   new directory
4e8e7a93628b4ed60aaaa47c6f72c1433f21e81dTimo Sirainen   -------------
4e8e7a93628b4ed60aaaa47c6f72c1433f21e81dTimo Sirainen
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi   If new/'s mtime is >= time() - MAILDIR_SYNC_SECS, always synchronize
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   it. dirty_cur_time-like feature might save us a few syncs, but
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi   that might break a client which saves a mail in one connection and
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   tries to fetch it in another one. new/ directory is almost always
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   empty, so syncing it should be very fast anyway. Actually this can
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   still happen if we sync only new/ dir while another client is also
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   moving mails from it to cur/ - it takes us a while to see them.
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   That's pretty unlikely to happen however, and only way to fix it
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   would be to always synchronize cur/ after new/.
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   Normally we move all mails from new/ to cur/ whenever we sync it. If
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   it's not possible for some reason, we mark the mail with "probably
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   exists in new/ directory" flag.
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   If rename() still fails because of ENOSPC or EDQUOT, we still save
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   the flag changes in index with dirty-flag on. When moving the mail
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   to cur/ directory, or when we notice it's already moved there, we
86bdb644d147a73df85abce4325254d694217a5fTimo Sirainen   apply the flag changes to the filename, rename it and remove the
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi   dirty flag. If there's dirty flags, this should be tried every time
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi   after expunge or when closing the mailbox.
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   uidlist
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   -------
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   This file contains UID <-> filename mappings. It's updated only when
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   new mail arrives, so it may contain filenames that have already been
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   deleted. Updating is done by getting uidlist.lock file, writing the
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   whole uidlist into it and rename()ing it over the old uidlist. This
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   means there's no need to lock the file for reading.
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   Whenever uidlist is rewritten, it's mtime must be larger than the old
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   one's. Use utime() before rename() if needed. Note that inode checking
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   wouldn't have been sufficient as inode numbers can be reused.
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   This file is usually read the first time you need to know filename for
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   given UID. After that it's not re-read unless new mails come that we
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   don't know about.
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   broken clients
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   --------------
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   Originally the middle identifier in Maildir filename was specified
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   only as <process id>_<delivery counter>. That however created a
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   problem with randomized PIDs which made it possible that the same
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   PID was reused within one second.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   So if within one second a mail was delivered, MUA moved it to cur/
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   and another mail was delivered by a new process using same PID as
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   the first one, we likely ended up overwriting the first mail when
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   the second mail was moved over it.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   Nowadays everyone should be giving a bit more specific identifier,
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   for example include microseconds in it which Dovecot does.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   There's a simple way to prevent this from happening in some cases:
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   Don't move the mail from new/ to cur/ if it's mtime is >= time() -
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   MAILDIR_SYNC_SECS. The second delivery's link() call then fails
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   because the file is already in new/, and it will then use a
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   different filename. There's a few problems with this however:
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen      - it requires extra stat() call which is unneeded extra I/O
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen      - another MUA might still move the mail to cur/
791fb70b3255a11a91ce0c2dc3ae1460d4cf8459Timo Sirainen      - if first file's flags are modified by either Dovecot or another
a18e2525cb076066784967d6c8118a01dd38ac6bTimo Sirainen        MUA, it's moved to cur/ (you _could_ just do the dirty-flagging
a18e2525cb076066784967d6c8118a01dd38ac6bTimo Sirainen    but that'd be ugly)
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen   Because this is useful only for very few people and it requires
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen   extra I/O, I decided not to implement this. It should be however
a18e2525cb076066784967d6c8118a01dd38ac6bTimo Sirainen   quite easy to do since we need to be able to deal with files in new/
a18e2525cb076066784967d6c8118a01dd38ac6bTimo Sirainen   in any case.
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen
2eccb2637d0153bb7f9ad39a70f254cece74342cTimo Sirainen   It's also possible to never accidentally overwrite a mail by using
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   link() + unlink() rather than rename(). This however isn't very
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   good idea as it introduces potential race conditions when multiple
202b4674243a4a4826c35ed4d089831985c47256Timo Sirainen   clients are accessing the mailbox:
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen   Trying to move the same mail from new/ to cur/ at the same time:
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen      a) Client 1 uses slightly different filename than client 2,
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen         for example one sets read-flag on but the other doesn't.
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen     You have the same mail duplicated now.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
95f5b08fa73ddd9a9de40a97aa141e9c74e0645eAki Tuomi      b) Client 3 sees the mail between Client 1's and 2's link() calls
95f5b08fa73ddd9a9de40a97aa141e9c74e0645eAki Tuomi         and changes it's flag. You have the same mail duplicated now.
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   And it gets worse when they're unlink()ing in cur/ directory:
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
95f5b08fa73ddd9a9de40a97aa141e9c74e0645eAki Tuomi      c) Client 1 changes mails's flag and client 2 changes it back
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen         between 1's link() and unlink(). The mail is now expunged.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen      d) If you try to deal with the duplicates by unlink()ing another
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen         one of them, you might end up unlinking both of them.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   So, what should we do then if we notice a duplicate? First of all,
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   it might not be a duplicate at all, readdir() might have just
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   returned it twice because it was just renamed. What we should do is
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   create a completely new base name for it and rename() it to that.
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen   If the call fails with ENOENT, it only means that it wasn't a
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen   duplicate after all.
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen*/
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "lib.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "ioloop.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "array.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "buffer.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "hash.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "str.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "eacces-error.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "nfs-workarounds.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "maildir-storage.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "maildir-uidlist.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "maildir-filename.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include "maildir-sync.h"
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include <stdio.h>
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include <stddef.h>
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include <stdlib.h>
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include <unistd.h>
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include <dirent.h>
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#include <sys/stat.h>
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen#define MAILDIR_FILENAME_FLAG_FOUND 128
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen/* When rename()ing many files from new/ to cur/, it's possible that next
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen   readdir() skips some files. we don't of course wish to lose them, so we
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen   go and rescan the new/ directory again from beginning until no files are
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen   left. This value is just an optimization to avoid checking the directory
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen   twice unneededly. usually only NFS is the problem case. 1 is the safest
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen   bet here, but I guess 5 will do just fine too. */
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen#define MAILDIR_RENAME_RESCAN_COUNT 5
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen/* This is mostly to avoid infinite looping when rename() destination already
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen   exists as the hard link of the file itself. */
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen#define MAILDIR_SCAN_DIR_MAX_COUNT 5
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen#define DUPE_LINKS_DELETE_SECS 30
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainenstruct maildir_sync_context {
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen        struct maildir_mailbox *mbox;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    const char *new_dir, *cur_dir;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    enum mailbox_sync_flags flags;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    time_t last_touch, last_notify;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    struct maildir_uidlist_sync_ctx *uidlist_sync_ctx;
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen    struct maildir_index_sync_context *index_sync_ctx;
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen
b7324e421e2132cbbf753e6fdbe675bbaecdf929Timo Sirainen    unsigned int partial:1;
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen    unsigned int locked:1;
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen};
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainenvoid maildir_sync_notify(struct maildir_sync_context *ctx)
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen{
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen    time_t now;
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen    if (ctx == NULL) {
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen        /* we got here from maildir-save.c. it has no
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen           maildir_sync_context,  */
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen        return;
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen    }
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen    now = time(NULL);
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen    if (now - ctx->last_touch > MAILDIR_LOCK_TOUCH_SECS && ctx->locked) {
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen        (void)maildir_uidlist_lock_touch(ctx->mbox->uidlist);
a18503d5dc0751a1f9785e48438a219d95c0b9c2Timo Sirainen        ctx->last_touch = now;
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen    }
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen    if (now - ctx->last_notify > MAIL_STORAGE_STAYALIVE_SECS) {
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen        struct mailbox *box = &ctx->mbox->box;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen        if (box->storage->callbacks.notify_ok != NULL) {
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen            box->storage->callbacks.
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen                notify_ok(box, "Hang in there..",
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen                      box->storage->callback_context);
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen        }
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen        ctx->last_notify = now;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    }
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen}
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainenstatic struct maildir_sync_context *
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainenmaildir_sync_context_new(struct maildir_mailbox *mbox,
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi             enum mailbox_sync_flags flags)
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi{
a01faca549a403b2eda938cea0b1fb76c3ff44b6Aki Tuomi        struct maildir_sync_context *ctx;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    ctx = t_new(struct maildir_sync_context, 1);
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    ctx->mbox = mbox;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    ctx->new_dir = t_strconcat(mbox->box.path, "/new", NULL);
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    ctx->cur_dir = t_strconcat(mbox->box.path, "/cur", NULL);
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen    ctx->last_touch = ioloop_time;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    ctx->last_notify = ioloop_time;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    ctx->flags = flags;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    return ctx;
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen}
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainenstatic void maildir_sync_deinit(struct maildir_sync_context *ctx)
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen{
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen    if (ctx->uidlist_sync_ctx != NULL)
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen        (void)maildir_uidlist_sync_deinit(&ctx->uidlist_sync_ctx, FALSE);
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen    if (ctx->index_sync_ctx != NULL)
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen        maildir_sync_index_rollback(&ctx->index_sync_ctx);
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen}
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainenstatic int maildir_fix_duplicate(struct maildir_sync_context *ctx,
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen                 const char *dir, const char *fname2)
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen{
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen    const char *fname1, *path1, *path2;
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen    const char *new_fname, *new_path;
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen    struct stat st1, st2;
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen    fname1 = maildir_uidlist_sync_get_full_filename(ctx->uidlist_sync_ctx,
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen                            fname2);
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen    i_assert(fname1 != NULL);
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen    path1 = t_strconcat(dir, "/", fname1, NULL);
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen    path2 = t_strconcat(dir, "/", fname2, NULL);
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen
4e8e7a93628b4ed60aaaa47c6f72c1433f21e81dTimo Sirainen    if (stat(path1, &st1) < 0 || stat(path2, &st2) < 0) {
7877db7b5daad125b6cb3e015574f33871c9a51bTimo Sirainen        /* most likely the files just don't exist anymore.
f6497ac81e6de57870936d538acccb75ce408fc1Timo Sirainen           don't really care about other errors much. */
f6ae9ae80a1fcf6c8f45ab759f0074caaa66c9c8Timo Sirainen        return 0;
736b1800b0409ba7443d33ecb8d0fb9f8b091660Timo Sirainen    }
10972f2a15f5538860fcc1d4adda227d59d2d757Timo Sirainen    if (st1.st_ino == st2.st_ino &&
bb869cc24b24a8df84a43154c628785d6aee784cTimo Sirainen        CMP_DEV_T(st1.st_dev, st2.st_dev)) {
ae9691f7ef36d5272d72c90fa51393dfea5dd126Timo Sirainen        /* 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->box.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)
{
    struct mailbox *box = &mbox->box;
    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(box))
            return -1;
        /* try again */
    }

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

static int
maildir_scan_dir(struct maildir_sync_context *ctx, bool new_dir, bool final)
{
    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 time_diff, i, readdir_count = 0, move_count = 0;
    time_t start_time;
    int ret = 1;
    bool move_new, 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->box))
            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

    start_time = time(NULL);
    if (new_dir) {
        ctx->mbox->maildir_hdr.new_check_time = start_time;
        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 = start_time;
        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->box) &&
        (ctx->mbox->box.flags & MAILBOX_FLAG_KEEP_RECENT) == 0 &&
        ctx->locked;

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

        flags = 0;
        if (move_new) {
            i_assert(dp->d_name[0] != '\0');

            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;
        }

        readdir_count++;
        if ((readdir_count % 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;
        }
    }

#ifdef __APPLE__
    if (errno == EINVAL && move_count > 0 && !final) {
        /* OS X HFS+: readdir() fails sometimes when rename()
           have been done. */
        move_count = MAILDIR_RENAME_RESCAN_COUNT + 1;
    } else
#endif

    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 >=
           "start_time", but just in case something weird happens and
           mtime doesn't update, use "start_time". */
        if (stat(ctx->new_dir, &st) == 0) {
            ctx->mbox->maildir_hdr.new_check_time =
                I_MAX(st.st_mtime, start_time);
            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, start_time);
            ctx->mbox->maildir_hdr.cur_mtime = st.st_mtime;
            ctx->mbox->maildir_hdr.cur_mtime_nsecs =
                ST_MTIME_NSEC(st);
        }
    }
    time_diff = time(NULL) - start_time;
    if (time_diff >= MAILDIR_SYNC_TIME_WARN_SECS) {
        i_warning("Maildir: Scanning %s took %u seconds "
              "(%u readdir()s, %u rename()s to cur/)",
              path, time_diff, readdir_count, move_count);
    }

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

static void maildir_sync_get_header(struct maildir_mailbox *mbox)
{
    const void *data;
    size_t data_size;

    mail_index_get_header_ext(mbox->box.view, mbox->maildir_ext_id,
                  &data, &data_size);
    if (data_size == 0) {
        /* header doesn't exist */
    } else {
        memcpy(&mbox->maildir_hdr, data,
               I_MIN(sizeof(mbox->maildir_hdr), data_size));
    }
}

int maildir_sync_header_refresh(struct maildir_mailbox *mbox)
{
    if (mail_index_refresh(mbox->box.index) < 0) {
        mail_storage_set_index_error(&mbox->box);
        return -1;
    }
    maildir_sync_get_header(mbox);
    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) {
        maildir_sync_get_header(mbox);
        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;

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

    uid_validity = maildir_uidlist_get_uid_validity(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 have_recent_messages(struct maildir_sync_context *ctx)
{
    const struct mail_index_header *hdr;

    (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->box.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)
{
    struct maildir_mailbox *mbox = ctx->mbox;
    enum mail_index_sync_flags flags = 0;
    bool undirty = (ctx->flags & MAILBOX_SYNC_FLAG_FULL_READ) != 0;

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

    if (have_recent_messages(ctx)) {
        if ((mbox->box.flags & MAILBOX_FLAG_KEEP_RECENT) == 0) {
            *new_changed_r = TRUE;
        } else if (*new_changed_r) {
            /* we have some recent messages and new/ has changed.
               if messages had been externally deleted from new/,
               we need to get them out of index. this requires that
               we make sure they weren't just moved to cur/. */
            *cur_changed_r = TRUE;
        }
    }

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

    if ((mbox->box.flags & MAILBOX_FLAG_KEEP_RECENT) == 0)
        flags |= MAIL_INDEX_SYNC_FLAG_DROP_RECENT;

    if (mbox->synced) {
        /* refresh index only after the first sync, i.e. avoid wasting
           time on refreshing it immediately after it was just opened */
        (void)mail_index_refresh(mbox->box.index);
    }
    return mail_index_sync_have_any(mbox->box.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;
    const char *fname;
    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->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->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;
        bool final = FALSE;

        while ((ret = maildir_scan_dir(ctx, TRUE, final)) > 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)
                final = TRUE;
        }
        if (ret < 0)
            return -1;

        if (cur_changed) {
            if (maildir_scan_dir(ctx, FALSE, TRUE) < 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 (ret < 0)
            maildir_sync_index_rollback(&ctx->index_sync_ctx);
        else if (maildir_sync_index_commit(&ctx->index_sync_ctx) < 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) {
        ret = maildir_uidlist_lookup_nosync(ctx->mbox->uidlist,
                            *find_uid, &flags, &fname);
        if (ret < 0)
            return -1;
        if (ret == 0) {
            /* 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, TRUE);
}

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) {
        if (mailbox_open(box) < 0)
            return index_mailbox_sync_init(box, flags, TRUE);
    }

    force_resync = (flags & MAILBOX_SYNC_FLAG_FORCE_RESYNC) != 0;
    if (index_mailbox_want_full_sync(&mbox->box, 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) ||
             (box->flags & MAILBOX_FLAG_KEEP_LOCKED) != 0);

        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->box.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->box);
            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);
    }
    mbox->synced = TRUE;
    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->box.path, "/new", NULL);
        cur_dir = t_strconcat(mbox->box.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);
}