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

On Feb 28, 2018, at 2:12 AM, Pavel Emelyanov [off-list ref] wrote:

On 02/27/2018 05:18 AM, Dmitry V. Levin wrote:

quoted

On Mon, Feb 26, 2018 at 12:02:25PM +0300, Pavel Emelyanov wrote:

quoted

On 02/21/2018 03:44 AM, Andrew Morton wrote:

quoted

On Tue,  9 Jan 2018 08:30:49 +0200 Mike Rapoport [off-list ref] wrote:

quoted

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?