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

[Leonardo Bras <leonardo@linux.ibm.com>]

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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
> > 
> 
> 

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