From: Pavel Machek <pavel@suse.cz>
To: mikulas@artax.karlin.mff.cuni.cz, clock@atrey.karlin.mff.cuni.cz,
kernel list <linux-kernel@vger.kernel.org>,
aviro@redhat.com
Subject: writing file to disk: not as easy as it looks
Date: Tue, 2 Dec 2008 10:40:59 +0100 [thread overview]
Message-ID: <20081202094059.GA2585@elf.ucw.cz> (raw)
Actually, it looks like POSIX file interface is on the lowest step of
Rusty's scale: one that is impossible to use correctly. Yes, it seems
impossible to reliably&safely write file to disk under Linux. Double
plus uncool.
So... how to write file to disk and wait for it to reach the stable
storage, with proper error handling?
> file
...does not work, because it fails to check for errors.
touch file || error_handling.
Is not a lot better, unless you mount your filesystems "sync"
... and noone does that.
dd conv=fsync if=something of=file 2> /dev/zero || error_handling
Is a bit better; not much, unless you mount your filesystems
"dirsync", because you have file data on disk, but they do not have
directory entry pointing to them. Noone uses dirsync.
So you need something like
dd conv=fsync if=something of=file 2> /dev/zero || error_handling
fsync . || error_handling
fsync .. || error_handling
fsync ../.. || error_handling
fsync ../../.. || error_handling
... which mostly works...
If you are alone on the filesystem... fsync only returns
errors to the first process. So if you have other process that
does fsync ., maybe it gets "your" error and you do not learn
of the problem.
Question is... Is there way that I missed and that actually works?
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
next reply other threads:[~2008-12-02 9:39 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-12-02 9:40 Pavel Machek [this message]
2008-12-02 14:04 ` writing file to disk: not as easy as it looks Theodore Tso
2008-12-02 15:26 ` Pavel Machek
2008-12-02 16:37 ` Theodore Tso
2008-12-02 17:22 ` Chris Friesen
2008-12-02 20:55 ` Theodore Tso
2008-12-02 22:44 ` Pavel Machek
2008-12-02 22:50 ` Pavel Machek
2008-12-03 5:07 ` Theodore Tso
2008-12-03 8:46 ` Pavel Machek
2008-12-03 15:50 ` Mikulas Patocka
2008-12-03 15:54 ` Alan Cox
2008-12-03 17:37 ` Mikulas Patocka
2008-12-03 17:52 ` Alan Cox
2008-12-03 18:16 ` Pavel Machek
2008-12-03 18:33 ` Mikulas Patocka
2008-12-03 16:42 ` Theodore Tso
2008-12-03 17:43 ` Mikulas Patocka
2008-12-03 18:26 ` Pavel Machek
2008-12-03 15:34 ` Mikulas Patocka
2008-12-15 10:24 ` [patch] " Pavel Machek
2008-12-15 11:03 ` Pavel Machek
2008-12-15 20:08 ` Folkert van Heusden
2008-12-02 19:10 ` Folkert van Heusden
2008-12-02 23:01 ` Mikulas Patocka
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