On Tue, 2016-05-10 at 00:00 -0700, Christoph Hellwig wrote:

On Mon, May 09, 2016 at 08:02:58AM -0400, Jeff Layton wrote:

quoted

quoted

quoted

AT_FORCE_ATTR_SYNC can be set in flags.????This will require a
network
filesystem to synchronise its attributes with the server.

AT_NO_ATTR_SYNC can be set in flags.????This will suppress
synchronisation
with the server in a network filesystem.????The resulting
values should be
considered approximate.

And what happens if neither is set?

I'd suggest we have the documentation state that the lack of either
flag leaves it up to the filesystem. In the case of NFS, you'd get
"normal" attribute cache behavior, for instance which is governed
by
the ac* attributes.

We should also note that in the case of something like
AT_NO_ATTR_SYNC
on NFS, you might _still_ end up talking to the server if the
client
has nothing in-core for that inode.

File systems specific "legacy" defaults are a bad idea.  If we can't
describe the semantics we should not allow them, never mind making
the the default.  I'd strongly suggest picking one of the above flags
as the default behavior and only allowing the other as optional flag.
I suspect NO_SYNC is the better one for the flag, as otherwise people
will be surprised once they test their default case on a network
filesystem.

Ok, that's a good point. So basically you suggest that xstat should
always have FORCE_SYNC semantics unless the NO_SYNC flag is set? Given
that we don't need to worry about legacy users with this interface,
that seems like a reasonable approach to me.
 
-- 
Jeff Layton [off-list ref]
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