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

To: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Subject: Re: [fuse-devel] utimensat fails to update ctime
From: Jean-Pierre André <jean-pierre.andre@xxxxxxxxxx>
Date: Tue, 22 Dec 2009 17:16:09 +0100
Cc: Eric Blake <ebb9@xxxxxxx>, fuse-devel@xxxxxxxxxxxxxxxxxxxxx, Miklos Szeredi <miklos@xxxxxxxxxx>, Christoph Hellwig <hch@xxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <87ljgvi1an.fsf@xxxxxxxxxxxxxxxxxxx>
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Hi again,

OGAWA Hirofumi wrote:
Jean-Pierre André<jean-pierre.andre@xxxxxxxxxx>  writes:

Hi again,
Hi,

Well, the problem seems in fuse_lib_setattr() and ntfs_fuse_setattr()
(lowlevel op too).

The both functions is requiring "ATIME | MTIME". Doesn't it mean the
ntfs-3g can't set only MTIME like above utimensat()?

With ntfs-3g this is not directly possible, because
the interface does not provide flags telling which
timestamps should be updated. The only way would
be fuse feeding both values (even though unchanged)
before calling ntfs-3g. This is true for all versions of
ntfs-3g.
Yes, with fuse_operations. It is why I'm saying the issue is libfuse or
ntfs-3g.

But I noticed ntfs-3g is including libfuse-lite sources and use it with
static link (I might be wrong here, because I just looked ntfs-3g source
slightly). AFAIK, the fuse of kernel part is passing the flags of some
sort of detail always.

Use of fuse-lite is optional, and static linking also
(both depend on your configure options),

[BTW, the code of that part in kernel may be the following,

fs/fuse/dir.c:iattr_to_fattr(),

[...]
So, if libfuse-lite was fixed to supported that update request, it would
be able to do even if fuse_operations.  I.e. in libfuse-lite, emulate
"ATIME | MTIME" request if "MTIME" only (pass unchanged original atime),
then call ->utime() callback. (or adds new utime2 callback with flags, or
something other solutions)

I will port to fuse-lite the patch which Miklos has
just sent.

Or, if that request is known limitation of fuse_operations, I think it
would be clear state and ok. The fs needs to use lowlevel op to support
that.

With lowntfs-3g (release candidate only), this could
be possible.... but this is not implemented, as the
case was never found up to now. I can provide you
with a patch,... if fuse can feed in the flags selectively.
Yes.  AFAIK, fuse of kernel part is passing FATTR_MTIME without
FATTR_ATIME to userland (i.e. FUSE_SET_ATTR_ATIME and
FUSE_SET_ATTR_MTIME in libfuse).

I think it's good to implement if it's not design decision of ntfs-3g.

[BTW, just my guess though, it would be good to use "if (vaild&
ATTR_XXX)" style, not "switch()" to support various combinations of
flags]

Might be better, ... or not. Setting both mtime
and atime is much simpler than setting each one
individually. So both methods will end up having
to process three different situations.

I suggest I port Miklos patch to fuse-lite soon,
and delay the low-level case (and microsecond
precision) until January. Does that suit your needs ?

Also : there is a common case of mis-configuration
in which gid is set in the mount options and uid
is not. As a consequence files appear as owned
by root and utime() is forbidden to plain users.

So you should first check your mount options.
And since ntfs-2009.11.14 standard ownership
and permissions are fully supported provided a
proper configuration file has been set.

Regards

Jean-Pierre



Thanks.

--
JP André
email jean-pierre.andre@xxxxxxxxxx




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