Subject: [nfsv4] rigged attributes

From: Stevan Steve Allen <[email-masked]>
Date: Thu, 21 Oct 2004 00:10:48 -0700

NFSv3 discusses filesystems which do not support the storing of some NFS
attributes on nonvolatile storage.  An example of the server assigning
CTIME=MTIME is provided if CTIME is not hardened.  We have file systems
which only stores create time, while others only store modified time.  With
the introduction of the v4 attribute mask, is it expected the server will
no longer return server generated attributes and let the client make the
more intelligent decision of determining a value for client applications?

note: in a cross mount environment, if the client PFS layer generates attrs
which are returned to a nfs server VFS layer, the server will not remove
these dummy attributes.

Thanks,
Stevan C. Allen

z/NFS Development: 5600 Cottle Rd. San Jose CA. 95193

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From: Spencer Shepler <[email-masked]>
Date: Thu, 21 Oct 2004 10:52:30 -0500

> more intelligent decision of determining a value for client applications?

The was the intent of the recommended attributes.  If the server can not
support them, it can then communicate this fact to the client and let it
decide what to do.  Obviously, mandatory attributes must be supported
by the server.

Spencer

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From: "J. Bruce Fields" <[email-masked]>
Date: Thu, 21 Oct 2004 12:06:20 -0400

> more intelligent decision of determining a value for client applications?

The section on recommended attributes (5.2) has some interesting
language:

	"It is expected that servers will support all attributes they
	comfortably can and only fail to support attributes which are
	difficult to support in their operating environments.  A server
	should provide attributes whenever they don't have to "tell
	lies" to the client.  For example, a file modification time
	should be either an accurate time or should not be supported by
	the server.  This will not always be comfortable to clients but
	the client is better positioned decide whether and how to
	fabricate or construct an attribute or whether to do without the
	attribute."

Though if a filesystem doesn't provide ctime then you do still have to
find a way to cook up the change attribute, as it's mandatory, not
recommended.

--b.