On Thu, Jun 29, 2017 at 01:34:22PM +0000, Marc-André Lureau wrote: > Hi > > On Wed, Jun 28, 2017 at 8:29 PM Eduardo Habkost <ehabk...@redhat.com> wrote: > > > On Tue, Jun 27, 2017 at 08:23:03AM +0000, Marc-André Lureau wrote: > > > Hi Eduardo > > > > > > On Fri, Jun 23, 2017 at 11:09 PM Eduardo Habkost <ehabk...@redhat.com> > > > wrote: > > > > > > > On Wed, Jun 21, 2017 at 04:02:18PM +0200, Marc-André Lureau wrote: > > > > > Add a new memory backend, similar to hostmem-file, except that it > > > > > doesn't need to create files. It also enforces memory sealing. > > > > > > > > > > This backend is mainly useful for sharing the memory with other > > > > > processes. > > > > > > > > How exactly can the memfd be used to share memory? Is there an > > existing > > > > mechanism for sharing the memfd file descriptor with another process > > > > > > > > > > > > Since there is no backing file, the traditional mechanism is by passing > > fd, > > > via socket ancillary data or forking etc.. Both ivshmem and vhost-user > > have > > > such messages, with eventually details for the memory map usage. > > > > The documentation is very similar to memory-backend-file, so it sounded > > like there was a generic mechanism to ask QEMU to share the backend FD. > > Maybe it would be interesting to mention on which cases the FD can > > actually be shared. Are ivshmem and vhost-user the only existing cases? > > > > > Actually, vhost-user may be the only way today to get the fd outside of > qemu process. > > (ivshmem needs the server to provide the fd) > > We could quite easily add or extend QMP messages for that in the future. > > Do you want this detail to be written in the commit message or elsewhere?
(Sorry for taking so long to reply.) I think this should be in the documentation of the new option (in qemu-options.hx). I don't think it needs lots of extra detail, maybe just change "which can be used to share the memory with a co-operating external process" to "which allows QEMU to share the memory with an external process in some cases (e.g. when using vhost-user)". -- Eduardo
