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Re: [OMPI devel] [PATCH v5 0/4] vm: add a syscall to map a process memory into a pipe
- From: "Atchley, Scott" <atchleyes at ornl dot gov>
- To: Open MPI Developers <devel at lists dot open-mpi dot org>
- Cc: Andrew Morton <akpm at linux-foundation dot org>, Mike Rapoport <rppt at linux dot vnet dot ibm dot com>, Alexander Viro <viro at zeniv dot linux dot org dot uk>, "linux-mm at kvack dot org" <linux-mm at kvack dot org>, "linux-fsdevel at vger dot kernel dot org" <linux-fsdevel at vger dot kernel dot org>, "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>, "linux-api at vger dot kernel dot org" <linux-api at vger dot kernel dot org>, "criu at openvz dot org" <criu at openvz dot org>, "gdb at sourceware dot org" <gdb at sourceware dot org>, "rr-dev at mozilla dot org" <rr-dev at mozilla dot org>, Arnd Bergmann <arnd at arndb dot de>, Michael Kerrisk <mtk dot manpages at gmail dot com>, Thomas Gleixner <tglx at linutronix dot de>, Josh Triplett <josh at joshtriplett dot org>, Jann Horn <jannh at google dot com>, Greg KH <gregkh at linuxfoundation dot org>, Andrei Vagin <avagin at openvz dot org>
- Date: Wed, 28 Feb 2018 23:12:03 +0000
- Subject: Re: [OMPI devel] [PATCH v5 0/4] vm: add a syscall to map a process memory into a pipe
- Authentication-results: sourceware.org; auth=none
- References: <1515479453-14672-1-git-send-email-rppt@linux.vnet.ibm.com> <20180220164406.3ec34509376f16841dc66e34@linux-foundation.org> <3122ec5a-7f73-f6b4-33ea-8c10ef32e5b0@virtuozzo.com> <20180227021818.GA31386@altlinux.org> <627ac4f8-a52d-0582-0c9e-e70ea667fa7e@virtuozzo.com>
> On Feb 28, 2018, at 2:12 AM, Pavel Emelyanov <xemul@virtuozzo.com> 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?
>
> -- Pavel
I may be completely off base, but could a FUSE daemon use this to read memory from the client and dump it to a file descriptor without copying the data into the kernel?