linux-kernel - Re: [PATCH v2] splice: sendfile() at once fails for big files

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Message-ID: <554A27F6.10800@kernel.dk>
Date:	Wed, 06 May 2015 08:40:54 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	leroy christophe <christophe.leroy@....fr>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
CC:	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>
Subject: Re: [PATCH v2] splice: sendfile() at once fails for big files

On 05/06/2015 08:38 AM, leroy christophe wrote:
>
> Le 06/05/2015 16:23, Jens Axboe a écrit :
>> On 05/05/2015 09:41 PM, Linus Torvalds wrote:
>>> Jens, ping?
>>>
>>> The test results should make this a no-brainer, but I hate how random
>>> these flag ops.
>>
>> Missed the original, apparently. I too am confused how this is a
>> correctness fix and not just an optimization.
>>
>> +               if (read_len < len)
>> +                       sd->flags |= SPLICE_F_MORE;
>> +               else if (!more)
>> +                       sd->flags &= ~SPLICE_F_MORE;
>>
>> Should that check be for 'more', not '!more'?
>>
>>
> @@ -1204,6 +1204,7 @@ ssize_t splice_direct_to_actor(struct file *in,
> struct splice_desc *sd,
>        * Don't block on output, we have to drain the direct pipe.
>        */
>       sd->flags &= ~SPLICE_F_NONBLOCK;
> +    more = sd->flags & SPLICE_F_MORE;
>
>       while (len) {
>           size_t read_len;
> @@ -1216,6 +1217,10 @@ ssize_t splice_direct_to_actor(struct file *in,
> struct splice_desc *sd,
>           read_len = ret;
>           sd->total_len = read_len;
>
> +        if (read_len < len)
> +            sd->flags |= SPLICE_F_MORE;
> +        else if (!more)
> +            sd->flags &= ~SPLICE_F_MORE;
>
>
>
> 'more' contains whether sendfile() has been called with SPLICE_F_MORE or
> not.
> Until all bytes are processed, we have to force SPLICE_F_MORE regardless
> of how sendfile() was called.
> Once all bytes have been read, we have to reset the flags according to
> how sendfile() was called, so if 'more' is NOT set, we have to clear
> SPLICE_F_MORE from sd->flags (which was unconditionaly set for
> processing the first bytes)

Ah gotcha, that looks correct. Patch is fine with me then.

-- 
Jens Axboe

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