linux-kernel - Re: [PATCH] pipe_to_sendpage: Ensure that MSG_MORE is set if we set MSG_SENDPAGE

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Date:	Sun, 24 Nov 2013 17:40:06 -0800
From:	Shawn Landden <shawnlandden@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Richard Weinberger <richard@....at>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
	linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Tom Herbert <therbert@...gle.com>,
	"David S. Miller" <davem@...emloft.net>, stable@...r.kernel.org
Subject: Re: [PATCH] pipe_to_sendpage: Ensure that MSG_MORE is set if we set MSG_SENDPAGE_NOTLAST

On Sun, Nov 24, 2013 at 5:25 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2013-11-25 at 00:42 +0100, Richard Weinberger wrote:
>> Commit 35f9c09fe (tcp: tcp_sendpages() should call tcp_push() once)
>> added an internal flag MSG_SENDPAGE_NOTLAST.
>> We have to ensure that MSG_MORE is also set if we set MSG_SENDPAGE_NOTLAST.
>> Otherwise users that check against MSG_MORE will not see it.
>>
>> This fixes sendfile() on AF_ALG.
>>
>> Cc: Tom Herbert <therbert@...gle.com>
>> Cc: Eric Dumazet <eric.dumazet@...il.com>
>> Cc: David S. Miller <davem@...emloft.net>
>> Cc: <stable@...r.kernel.org> # 3.4.x
>> Reported-and-tested-by: Shawn Landden <shawnlandden@...il.com>
>> Signed-off-by: Richard Weinberger <richard@....at>
>> ---
>>  fs/splice.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/splice.c b/fs/splice.c
>> index 3b7ee65..b93f1b8 100644
>> --- a/fs/splice.c
>> +++ b/fs/splice.c
>> @@ -701,7 +701,7 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe,
>>       more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
>>
>>       if (sd->len < sd->total_len && pipe->nrbufs > 1)
>> -             more |= MSG_SENDPAGE_NOTLAST;
>> +             more |= MSG_SENDPAGE_NOTLAST | MSG_MORE;
>>
>>       return file->f_op->sendpage(file, buf->page, buf->offset,
>>                                   sd->len, &pos, more);
>
> I do not think this patch is right. It looks like a revert of a useful
> patch for TCP zero copy. Given the time it took to discover this
> regression, I bet tcp zero copy has more users than AF_ALG, by 5 or 6
> order of magnitude ;)
>
> Here we want to make the difference between the two flags, not merge
> them.
>
> If AF_ALG do not care of the difference, try instead :
>
> diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
> index ef5356cd280a..850246206b12 100644
> --- a/crypto/algif_hash.c
> +++ b/crypto/algif_hash.c
> @@ -114,6 +114,9 @@ static ssize_t hash_sendpage(struct socket *sock, struct page *page,
>         struct hash_ctx *ctx = ask->private;
>         int err;
>
> +       if (flags & MSG_SENDPAGE_NOTLAST)
> +               flags |= MSG_MORE;
> +
>         lock_sock(sk);
>         sg_init_table(ctx->sgl.sg, 1);
>         sg_set_page(ctx->sgl.sg, page, size, offset);
>

>From my testing this works.

-- 

---
Shawn Landden
+1 360 389 3001 (SMS preferred)
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