linux-kernel - Re: [PATCH v5 0/4] vm: add a syscall to map a process memory into a pipe

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Message-ID: <20180228175035.GA20686@outlook.office365.com>
Date:   Wed, 28 Feb 2018 09:50:36 -0800
From:   Andrei Vagin <avagin@...tuozzo.com>
To:     Pavel Emelyanov <xemul@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Alexander Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, criu@...nvz.org, gdb@...rceware.org,
        devel@...ts.open-mpi.org, rr-dev@...illa.org,
        Arnd Bergmann <arnd@...db.de>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Triplett <josh@...htriplett.org>,
        Jann Horn <jannh@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrei Vagin <avagin@...nvz.org>
Subject: Re: [PATCH v5 0/4] vm: add a syscall to map a process memory into a
 pipe

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@...ux.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