Re: [Qemu-devel] QEMU patch to allow VM introspection via libvmi

[Eduardo Habkost]

On Thu, Oct 22, 2015 at 01:57:13PM -0600, Valerio Aimale wrote:
> On 10/22/15 1:12 PM, Eduardo Habkost wrote:
> >On Wed, Oct 21, 2015 at 12:54:23PM +0200, Markus Armbruster wrote:
> >>Valerio Aimale <address@hidden> writes:
> >[...]
> >>>There's also a similar patch, floating around the internet, the uses
> >>>shared memory, instead of sockets, as inter-process communication
> >>>between libvmi and QEMU. I've never used that.
> >>By the time you built a working IPC mechanism on top of shared memory,
> >>you're often no better off than with AF_LOCAL sockets.
> >>
> >>Crazy idea: can we allocate guest memory in a way that support sharing
> >>it with another process?  Eduardo, can -mem-path do such wild things?
> >It can't today, but just because it creates a temporary file inside
> >mem-path and unlinks it immediately after opening a file descriptor. We
> >could make memory-backend-file also accept a full filename as argument,
> >or add a mechanism to let QEMU send the open file descriptor to a QMP
> >client.
> >
> Eduardo, would my "artisanal" idea of creating an mmap'ed image of the guest
> memory footprint work, augmented by Eric's suggestion of having the qmp
> client pass the filename?

The code below doesn't make sense to me.

> 
> qmp_pmemmap( [...]) {
> 
>     char *template = "/tmp/QEM_mmap_XXXXXXX";
>     int mmap_fd;
>     uint8_t *local_memspace = malloc( (size_t) 8589934592 /* assuming VM
> with 8GB RAM */);
> 
>     cpu_physical_memory_rw( (hwaddr) 0,  local_memspace , (hwaddr)
> 8589934592 /* assuming VM with 8GB RAM */, 0 /* no write for now will
> discuss write later */);

Are you suggesting copying all the VM RAM contents to a whole new area?
Why?

> 
>    mmap_fd = mkstemp("/tmp/QEUM_mmap_XXXXXXX");
> 
>    mmap((void *) local_memspace, (size_t) 8589934592, PROT_READ |
> PROT_WRITE,  MAP_SHARED | MAP_ANON,  mmap_fd, (off_t) 0);

I don't understand what you are trying to do here.

> 
>   /* etc */
> 
> }
> 
> pmemmap would return the following json
> 
> {
>     'success' : 'true',
>     'map_filename' : '/tmp/QEM_mmap_1234567'
> }
> 
> 

-- 
Eduardo