linux-kernel - Re: [fuse-devel] utimensat fails to update ctime

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Message-ID: <87vdfxmr4f.fsf@devron.myhome.or.jp>
Date:	Thu, 24 Dec 2009 04:23:28 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Eric Blake <ebb9@....net>
Cc:	Jean-Pierre André 
	<jean-pierre.andre@...adoo.fr>, fuse-devel@...ts.sourceforge.net,
	Miklos Szeredi <miklos@...redi.hu>,
	Christoph Hellwig <hch@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	xfs@....sgi.com, ctrn3e8 <ctrn3e8@...il.com>,
	bug-coreutils <bug-coreutils@....org>
Subject: Re: [fuse-devel] utimensat fails to update ctime

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

> By the way, is there any reliable way, other than uname() and checking for
> a minimum kernel version, to tell if all file systems will properly
> support UTIME_OMIT?

Um... sorry, I don't know. And it might be hard to detect efficiently if
the workaround is enough efficient like one fstat() syscall (Pass fd to
kernel.  I.e. just read from cached inode).

> For coreutils 8.3, we will be inserting a workaround where instead of
> using UTIME_OMIT, we call fstatat() in advance of utimensat() and pass
> the original timestamp down.  But it would be nice to avoid the
> penalty of the extra stat if there were a reliable way to ensure that,
> regardless of file system, the use of UTIME_OMIT will be honored.
> After all, coreutils wants touch(1) to work regardless of how old the
> user's kernel and file system drivers are.

Or it would depend on coreutils policy though, personally I think it's
ok that it ignores the bug as known fs bug, otherwise coreutils would
need to collect workarounds on several filesystems of several OSes.

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