From: David Howells <dhowells@redhat.com>
To: Matthew Wilcox <willy@infradead.org>, Al Viro <viro@zeniv.linux.org.uk>
Cc: dhowells@redhat.com, jlayton@kernel.org,
linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] afs: Fix afs_write_end() to handle short writes
Date: Mon, 14 Jun 2021 14:37:12 +0100 [thread overview]
Message-ID: <466590.1623677832@warthog.procyon.org.uk> (raw)
In-Reply-To: <YMdZbsvBNYBtZDC2@casper.infradead.org>
Matthew Wilcox <willy@infradead.org> wrote:
> > (1) If the page is not up to date, then we should just return 0
> > (ie. indicating a zero-length copy). The loop in
> > generic_perform_write() will go around again, possibly breaking up the
> > iterator into discrete chunks.
>
> Does this actually work? What about the situation where you're reading
> the last page of a file and thus (almost) always reading fewer bytes
> than a PAGE_SIZE?
Al Viro made such a change for Ceph - and we're writing, not reading.
I was thinking that it would break if reading from a pipe, but Jeff pointed
out that the iov_iter_advance() in generic_perform_write() uses the return
value of ->write_end() to advance the iterator. So it might loop endlessly,
but it doesn't appear it will corrupt your data.
David
next prev parent reply other threads:[~2021-06-14 13:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-14 13:20 [PATCH 1/3] afs: Handle len being extending over page end in write_begin/write_end David Howells
2021-06-14 13:20 ` [PATCH 2/3] afs: Fix afs_write_end() to handle short writes David Howells
2021-06-14 13:28 ` Matthew Wilcox
2021-06-14 13:37 ` David Howells [this message]
2021-06-14 13:46 ` Matthew Wilcox
2021-06-18 3:40 ` Al Viro
2021-06-14 14:04 ` David Howells
2021-06-14 14:37 ` Matthew Wilcox
2021-06-14 15:38 ` David Howells
2021-06-14 15:43 ` Matthew Wilcox
2021-06-14 21:11 ` David Howells
2021-06-14 13:20 ` [PATCH 3/3] netfs: fix test for whether we can skip read when writing beyond EOF David Howells
2021-06-15 17:01 ` Jeff Layton
2021-06-14 13:33 ` David Howells
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