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Date:   Wed, 28 Feb 2018 09:50:36 -0800
From:   Andrei Vagin <avagin@virtuozzo.com>
To:     Pavel Emelyanov <xemul@virtuozzo.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
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        Josh Triplett <josh@joshtriplett.org>,
        Jann Horn <jannh@google.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andrei Vagin <avagin@openvz.org>
Subject: Re: [PATCH v5 0/4] vm: add a syscall to map a process memory into a
 pipe
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On Wed, Feb 28, 2018 at 10:12:55AM +0300, Pavel Emelyanov wrote:
> On 02/27/2018 05:18 AM, Dmitry V. Levin wrote:
> > On Mon, Feb 26, 2018 at 12:02:25PM +0300, Pavel Emelyanov wrote:
> >> On 02/21/2018 03:44 AM, Andrew Morton wrote:
> >>> On Tue,  9 Jan 2018 08:30:49 +0200 Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:
> >>>
> >>>> This patches introduces new process_vmsplice system call that combines
> >>>> functionality of process_vm_read and vmsplice.
> >>>
> >>> All seems fairly strightforward.  The big question is: do we know that
> >>> people will actually use this, and get sufficient value from it to
> >>> justify its addition?
> >>
> >> Yes, that's what bothers us a lot too :) I've tried to start with finding out if anyone 
> >> used the sys_read/write_process_vm() calls, but failed :( Does anybody know how popular
> >> these syscalls are?
> > 
> > Well, process_vm_readv itself is quite popular, it's used by debuggers nowadays,
> > see e.g.
> > $ strace -qq -esignal=none -eprocess_vm_readv strace -qq -o/dev/null cat /dev/null
> 
> I see. Well, yes, this use-case will not benefit much from remote splice. How about more
> interactive debug by, say, gdb? It may attach, then splice all the memory, then analyze
> the victim code/data w/o copying it to its address space?

Hmm, in this case, you probably will want to be able to map pipe pages
into memory.

> 
> -- Pavel