On Tue, 2020-12-01 at 03:16 +0000, Trond Myklebust wrote: > On Mon, 2020-11-30 at 22:11 -0500, bfields@xxxxxxxxxxxx wrote: > > On Tue, Dec 01, 2020 at 03:06:46AM +0000, Trond Myklebust wrote: > > > A local filesystem might choose to set the 'non-atomic' flag > > > without > > > wanting to turn off NFSv3 WCC attributes. Yes, the latter are > > > assumed > > > to be atomic, but a number of commercial servers do abuse that > > > assumption in practice. > > > > What do you mean by abusing that assumption? > > > > I thought that leaving off the post-op attrs was the v3 protocol's > > way > > of saying that it couldn't give you atomic wcc information. > > > > I mean that a number of commercial servers will happily return NFSv3 > pre/post-operation WCC information that is not atomic with the > operation that is supposed to be 'protected'. This is, after all, why > the NFSv4 "struct change_info4" added the 'atomic' field in the first > place. BTW: To be fair, so does knfsd... At Hammerspace, we had some real problems recently due to XFS exports returning non-atomic values for the "space used" field. Speculative preallocation is a real bitch: https://xfs.org/index.php/XFS_FAQ#Q:_What_is_speculative_preallocation.3F -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
