Re: [PATCH] vmsplice.2: SPLICE_F_GIFT became no-op

[Jens Axboe <axboe@kernel.dk>]

Sorry, better late than never?

He's right, Nick Piggin removed that flag (and promised to reinstate it,
but a decade later I'm not holding my breath).


On 12/17/19 2:12 PM, Leonardo Bras wrote:
> On Fri, 2019-09-13 at 14:55 +0200, Michael Kerrisk (man-pages) wrote:
>> Hello Jens,
>>
>> Would you be willing to take a look at this man-pages bug report
>> relating to vmsplice()?
> 
> Hello Jens,
> 
> Could you please provide feedback on this patch?
> 
> Thank you,
> Leonardo Bras
> 
> 
>>
>> Thanks,
>>
>> Michael
>>
>> On 8/2/19 12:24 AM, Leonardo Bras wrote:
>>> As explained in splice.2, SPLICE_F_MOVE became a no-op, and since it
>>> is needed to use page gifting, it made SPLICE_F_GIFT a no-op too.
>>>
>>> I took a look in current code, and found no use of this flag:
>>> When enabled, it sets PIPE_BUF_FLAG_GIFT,which is only checked in
>>> user_page_pipe_buf_steal, which is only used on
>>> user_page_pipe_buf_ops, as a .steal component.
>>>
>>> But, in the whole kernel code, there is no calling of a steal()
>>> function, making me believe this flag is not used anymore.
>>>
>>> Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
>>> ---
>>>  man2/vmsplice.2 | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>> diff --git a/man2/vmsplice.2 b/man2/vmsplice.2
>>> index 17834607b..94fb86142 100644
>>> --- a/man2/vmsplice.2
>>> +++ b/man2/vmsplice.2
>>> @@ -123,6 +123,11 @@ if this flag is not specified, then a subsequent
>>>  .B SPLICE_F_MOVE
>>>  must copy the pages.
>>>  Data must also be properly page aligned, both in memory and length.
>>> +Starting in Linux 2.6.21, it is a no-op, because the
>>> +.B SPLICE_F_MOVE
>>> +also became a no-op on
>>> +.BR splice (2)
>>> +.
>>>  .\" FIXME
>>>  .\" It looks like the page-alignment requirement went away with
>>>  .\" commit bd1a68b59c8e3bce45fb76632c64e1e063c3962d
>>>
>>
>>


-- 
Jens Axboe