linux-kernel - Re: [PATCH -next 1/2] nfs: nfs{,4}_file_flush should consume writeback error

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Date:   Tue, 12 Apr 2022 13:56:07 +0000
From:   Trond Myklebust <trondmy@...merspace.com>
To:     "anna@...nel.org" <anna@...nel.org>,
        "chenxiaosong2@...wei.com" <chenxiaosong2@...wei.com>,
        "smayhew@...hat.com" <smayhew@...hat.com>
CC:     "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "liuyongqiang13@...wei.com" <liuyongqiang13@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yi.zhang@...wei.com" <yi.zhang@...wei.com>,
        "zhangxiaoxu5@...wei.com" <zhangxiaoxu5@...wei.com>
Subject: Re: [PATCH -next 1/2] nfs: nfs{,4}_file_flush should consume
 writeback error

On Tue, 2022-04-12 at 21:46 +0800, chenxiaosong (A) wrote:
> 在 2022/3/6 23:08, Trond Myklebust 写道:
> > 
> > Just to clarify a little.
> > 
> > I don't see a need to consume the writeback errors on close(),
> > unless
> > other filesystems do the same. If the intention is that fsync()
> > should
> > see _all_ errors that haven't already been seen, then NFS should
> > follow
> > the same semantics as all the other filesystems.
> > 
> 
> Other filesystem will _not_ clear writeback error on close().
> And other filesystem will _not_ clear writeback error on async
> write() too.
> 
> Other filesystem _only_ clear writeback error on fsync() or sync
> write().
> 

Yes. We might even consider not reporting writeback errors at all in
close(), since most developers don't check it. We certainly don't want
to clear those errors there because the manpages don't document that as
being the case.

> Should NFS follow the same semantics as all the other filesystems?

It needs to follow the semantics described in the manpage for write(2)
and fsync(2) as closely as possible, yes. That documentation is
supposed to be normative for application developers.

We won't guarantee to immediately report ENOSPC like other filesystems
do (because that would require us to only support synchronous writes),
however that behaviour is already documented in the manpage.

We may also report some errors that are not documented in the manpage
(e.g. EACCES or EROFS) simply because those errors cannot always be
reported at open() time, as would be the case for a local filesystem.
That's just how the NFS protocol works (particularly for the case of
the stateless NFSv3 protocol).

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@...merspace.com