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From: Matthew Wilcox <willy@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: 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 14:28:14 +0100	[thread overview]
Message-ID: <YMdZbsvBNYBtZDC2@casper.infradead.org> (raw)
In-Reply-To: <162367682522.460125.5652091227576721609.stgit@warthog.procyon.org.uk>

On Mon, Jun 14, 2021 at 02:20:25PM +0100, David Howells wrote:
> Fix afs_write_end() to correctly handle a short copy into the intended
> write region of the page.  Two things are necessary:
> 
>  (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?

>      This is analogous to commit b9de313cf05fe08fa59efaf19756ec5283af672a
>      for ceph.
> 
>  (2) The page should not have been set uptodate if it wasn't completely set
>      up by netfs_write_begin() (this will be fixed in the next page), so we
>      need to set PG_uptodate here in such a case.

s/page/patch/

and you have a really bad habit of breaking the layering and referring
to PG_foo.  Please just refer to PageFoo.  Filesystems shouldn't
care what the implementation of PageFoo is.

> +	len = min_t(size_t, len, thp_size(page) - from);
> +	if (!PageUptodate(page)) {
> +		if (copied < len) {
> +			copied = 0;
> +			goto out;
> +		}
> +
> +		SetPageUptodate(page);
> +	}

  reply	other threads:[~2021-06-14 13:28 UTC|newest]

Thread overview: 15+ 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 [this message]
2021-06-14 13:37   ` David Howells
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
2021-06-17  7:43 ` [PATCH 1/3] afs: Handle len being extending over page end in write_begin/write_end kernel test robot

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