On Fri, 2020-03-13 at 12:11 +0100, Mkrtchyan, Tigran wrote: > Hi Frank, > > I think the way how you have implemented is almost correct. You query > server for supported attributes. As result client will get all > attributes > supported bu the server and if FATTR4_XATTR_SUPPORT is returned, then > client > adds xattr capability. This the way how I read rfc8276. Do you have a > different > opinion? > 'xattr_support' seems like a protocol hack to allow the client to determine whether or not the xattr operations are supported. The reason why it is a hack is that 'supported_attrs' is also a per- filesystem attribute, and there is no value in advertising 'xattr_support' there unless your filesystem also supports xattrs. IOW: the protocol forces you to do 2 round trips to the server in order to figure out something that really should be obvious with 1 round trip. > Regards, > Tigran. > > ----- Original Message ----- > > From: "Frank van der Linden" <fllinden@xxxxxxxxxx> > > To: "Tigran Mkrtchyan" <tigran.mkrtchyan@xxxxxxx> > > Cc: "Trond Myklebust" <trond.myklebust@xxxxxxxxxxxxxxx>, "Anna > > Schumaker" <anna.schumaker@xxxxxxxxxx>, "linux-nfs" > > <linux-nfs@xxxxxxxxxxxxxxx> > > Sent: Thursday, March 12, 2020 10:15:55 PM > > Subject: Re: [PATCH 03/13] NFSv4.2: query the server for extended > > attribute support > > On Thu, Mar 12, 2020 at 08:51:39PM +0000, Frank van der Linden > > wrote: > > > 1) The xattr_support attribute exists > > > 2) The xattr support attribute exists *and* it's true for the > > > root fh > > > > > > Currently the code does 2) in one operation. That might not be > > > 100% > > > correct - the RFC does mention that (section 8.2): > > > > > > "Before interrogating this attribute using GETATTR, a client > > > should > > > determine whether it is a supported attribute by interrogating > > > the > > > supported_attrs attribute." > > > > > > That's a "should", not a "MUST", but it's still waving its finger > > > at you not to do this. > > > > > > Since 8.2.1 says: > > > > > > "However, a client may reasonably assume that a server > > > (or file system) that does not support the xattr_support > > > attribute > > > does not provide xattr support, and it acts on that basis." > > > > > > ..I think you're right, and the code should just use the > > > existence > > > of the attribute as a signal that the server knows about xattrs - > > > operations should still error out correctly if it doesn't. > > > > > > I'll make that change, thanks. > > > > ..or, alternatively, only query xattr_support in > > nfs4_server_capabilities, > > and then its actual value, if it exists, in nfs4_fs_info. > > > > Any opinions on this? > > > > - Frank -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
