Messages in this thread Patch in this message | | | Date | Sun, 12 Mar 2006 16:28:43 +0000 (GMT) | From | Anton Altaparmakov <> | Subject | [2.6 PATCH]: Incorrect lack of {m,c}time modification for ftruncate. |
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Hi,
Recently Neil Brown's patch to fix the standards compliance of setting {m,c}time on {f,}truncate and open(O_TRUNC) was applied to the kernel.
See http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=4a30131e7dbb17e5fec6958bfac9da9aff1fa29b
From the patch description: <quote> SUS requires that when truncating a file to the size that it currently is: truncate and ftruncate should NOT modify ctime or mtime O_TRUNC SHOULD modify ctime and mtime. [snip] With this patch: ATTR_CTIME|ATTR_MTIME are sent with ATTR_SIZE precisely when an update of these times is required whether size changes or not (via a new argument to do_truncate). This allows NFS to do the right thing for O_TRUNC. inode_setattr nolonger forces ATTR_MTIME|ATTR_CTIME when the ATTR_SIZE sets the size to it's current value. This allows local filesystems to do the right thing for f?truncate. </quote>
The problem with this patch is that the standard does not actually say the above, it in fact says that:
- both open(O_TRUNC) and ftruncate() _always_ modify {m,c}time and
- truncate() modifies {m,c}time _only_ if the file size changes due to the truncate.
(This IMO is completely brain damaged... but I guess no-one claims standards are not braindamaged...)
Here are the relevant three pages from posix/sus3 together with the relevant paragraph quoted:
http://www.opengroup.org/onlinepubs/009695399/functions/open.html <quote> If O_TRUNC is set and the file did previously exist, upon successful completion, open() shall mark for update the st_ctime and st_mtime fields of the file. </quote>
http://www.opengroup.org/onlinepubs/009695399/functions/ftruncate.html <quote> Upon successful completion, if fildes refers to a regular file, the ftruncate() function shall mark for update the st_ctime and st_mtime fields of the file and the S_ISUID and S_ISGID bits of the file mode may be cleared. If the ftruncate() function is unsuccessful, the file is unaffected. </quote>
http://www.opengroup.org/onlinepubs/009695399/functions/truncate.html <quote> Upon successful completion, if the file size is changed, this function shall mark for update the st_ctime and st_mtime fields of the file, and the S_ISUID and S_ISGID bits of the file mode may be cleared. </quote>
So at present we handle open(O_TRUNC) and truncate() correctly but we do the Wrong Thing (TM) for ftruncate().
This is fixed by the simple one liner patch at the bottom of this email.
Please apply or tell me that I can't read the standard and kindly point out to me what I have missed... (-:
Best regards,
Anton -- Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @) Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/
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Cause the {m,c}time to always be updated when ftruncate() is called as required by posix/sus3.
Signed-off-by: Anton Altaparmakov <aia21@cantab.net>
diff -urNp linux-2.6/fs/open.c.old linux-2.6/fs/open.c --- linux-2.6/fs/open.c.old 2006-03-12 16:09:26.000000000 +0000 +++ linux-2.6/fs/open.c 2006-03-12 16:10:41.000000000 +0000 @@ -321,7 +321,8 @@ static long do_sys_ftruncate(unsigned in error = locks_verify_truncate(inode, file, length); if (!error) - error = do_truncate(dentry, length, 0, file); + error = do_truncate(dentry, length, ATTR_MTIME | ATTR_CTIME, + file); out_putf: fput(file); out: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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