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

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Message-ID: <554A2E1F.7010102@kernel.dk>
Date:	Wed, 06 May 2015 09:07:11 -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 08:40 AM, Jens Axboe wrote:
> 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.

Needs a comment added to that effect, imho.

-- 
Jens Axboe

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