Messages in this thread | | | Date | Tue, 2 Dec 2008 10:40:59 +0100 | From | Pavel Machek <> | Subject | writing file to disk: not as easy as it looks |
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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
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