linux-kernel - Re: utimensat fails to update ctime

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Date:	Tue, 22 Dec 2009 18:00:36 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Eric Blake <ebb9@....net>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	xfs@....sgi.com, Christoph Hellwig <hch@....de>,
	Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel@...ts.sourceforge.net
Subject: Re: utimensat fails to update ctime

Eric Blake <ebb9@....net> writes:

> According to OGAWA Hirofumi on 12/21/2009 8:05 AM:
>>> It may also be file-system dependent.  On the machine where I saw the
>>> original failure:
>>>> $ uname -a
>>>> Linux fencepost 2.6.26-2-xen-amd64 #1 SMP Thu Nov 5 04:27:12 UTC 2009
>>>> x86_64 GNU/Linux
>>> $ df -T .
>>> Filesystem    Type   1K-blocks      Used Available Use% Mounted on
>>> /dev/sdb1      xfs   419299328 269018656 150280672  65% /srv/data
>> 
>> Thanks.
>> 
>> This is good point. This would be xfs issue or design. xfs seems to have
>> own special handling of ctime.
>
> Here's another report, this time about an mtime update not happening on
> ntfs-3g.  http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/19336

It is likely the issue of libfuse or ntfs-3g. I don't know about ntfs-3g
people at all. So, for now, just Cc: to fuse people.

> utimensat(0, NULL, {UTIME_OMIT, UTIME_NOW}, 0) = 0

>From this, "ia_valid" will have "ATTR_CTIME | ATTR_MTIME". And the
request would pass to userland via fuse of kernel part, then it will be
handled by libfuse.

>From quick grep of libfuse and ntfs-3g (would not be latest), ntfs-3g is
using "struct fuse_operations", not "struct fuse_lowlevel_ops".

So, fuse_lib_setattr() would be the handler for it in libfuse. And, from
the following part, it seems to require the both of MTIME and ATIME to
call ntfs-3g's ->utime handler.

I don't know whether it is limitation or bug in fuse_operations.
Any ideas?

		if (!err &&
		    (valid & (FUSE_SET_ATTR_ATIME | FUSE_SET_ATTR_MTIME)) ==
		    (FUSE_SET_ATTR_ATIME | FUSE_SET_ATTR_MTIME)) {
			struct timespec tv[2];
			tv[0].tv_sec = attr->st_atime;
			tv[0].tv_nsec = ST_ATIM_NSEC(attr);
			tv[1].tv_sec = attr->st_mtime;
			tv[1].tv_nsec = ST_MTIM_NSEC(attr);
			err = fuse_fs_utimens(f->fs, path, tv);
		}

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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