Re: [OMPI devel] [PATCH v5 0/4] vm: add a syscall to map a process memory into a pipe

Atchley, Scott
2018-02-28T23:12:09Z

> 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?