----- Original Message -----
> On Tue, 12 Apr 2016 13:55:28 +0200
> marcandre.lur...@redhat.com wrote:
>
> > From: Marc-André Lureau <marcandre.lur...@redhat.com>
> >
> > Add a new memory backend, similar to hostmem-file, except that it
> > doesn't need a file path, or hugepages directory permissions. It also
> > try to enforce memory sealing if available.
> >
> > This backend is mainly useful for easily sharing the memory with other
> > processes, for example with vhost-user backend, when hugepages aren't
> > available (for security reasons and other limitations).
> >
> > Usage:
> > -object memory-backend-memfd,id=mem1,size=1G
> Does it make sense if it's possible to reuse/extend memory-backend-file,
> i.e. make 'mem-path' optional and behave like this patch
> and also add 'memfd' property so that parent process could
> pass its handle to QEMU as well?
I don't mind, I would be a bit worried by the combination of options and the
expected result though.
> >
> > Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> > ---
> > backends/Makefile.objs | 1 +
> > backends/hostmem-memfd.c | 85
> > ++++++++++++++++++++++++++++++++++++++++++++++++
> > qemu-options.hx | 12 +++++++
> > 3 files changed, 98 insertions(+)
> > create mode 100644 backends/hostmem-memfd.c
> >
> > diff --git a/backends/Makefile.objs b/backends/Makefile.objs
> > index 31a3a89..32cfcdb 100644
> > --- a/backends/Makefile.objs
> > +++ b/backends/Makefile.objs
> > @@ -9,3 +9,4 @@ common-obj-$(CONFIG_TPM) += tpm.o
> >
> > common-obj-y += hostmem.o hostmem-ram.o
> > common-obj-$(CONFIG_LINUX) += hostmem-file.o
> > +common-obj-$(CONFIG_POSIX) += hostmem-memfd.o
> > diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
> > new file mode 100644
> > index 0000000..e0e18d7
> > --- /dev/null
> > +++ b/backends/hostmem-memfd.c
> > @@ -0,0 +1,85 @@
> > +/*
> > + * QEMU host memfd memory backend
> > + *
> > + * Copyright (C) 2016 Red Hat Inc
> > + *
> > + * Authors:
> > + * Marc-André Lureau <marcandre.lur...@redhat.com>
> > + *
> > + * This work is licensed under the terms of the GNU GPL, version 2 or
> > later.
> > + * See the COPYING file in the top-level directory.
> > + */
> > +#include "qemu/osdep.h"
> > +#include "qemu-common.h"
> > +#include "sysemu/hostmem.h"
> > +#include "sysemu/sysemu.h"
> > +#include "qom/object_interfaces.h"
> > +#include "qemu/memfd.h"
> > +#include "qapi/error.h"
> > +
> > +/**
> > + * @TYPE_MEMORY_BACKEND_MEMFD:
> > + * name of the memory backend that uses memfd mmap
> > + */
> > +#define TYPE_MEMORY_BACKEND_MEMFD "memory-backend-memfd"
> > +
> > +#define MEMORY_BACKEND_MEMFD(obj) \
> > + OBJECT_CHECK(HostMemoryBackendMemfd, (obj), TYPE_MEMORY_BACKEND_MEMFD)
> > +
> > +typedef struct HostMemoryBackendMemfd HostMemoryBackendMemfd;
> > +
> > +struct HostMemoryBackendMemfd {
> > + HostMemoryBackend parent_obj;
> > +
> > + int fd;
> > +};
> > +
> > +static void
> > +memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
> > +{
> > + int fd;
> > +
> > + if (!backend->size) {
> > + error_setg(errp, "can't create backend with size 0");
> > + return;
> > + }
> > +#ifndef CONFIG_LINUX
> > + error_setg(errp, "memfd not supported on this host");
> > +#else
> > + if (!memory_region_size(&backend->mr)) {
> > + backend->force_prealloc = mem_prealloc;
> > + fd = qemu_memfd_create(TYPE_MEMORY_BACKEND_MEMFD,
> > + backend->size,
> > + F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL);
> > + if (fd == -1) {
> > + error_setg(errp, "can't allocate memfd backend");
> > + return;
> > + }
> > + memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend),
> > + object_get_canonical_path(OBJECT(backend)),
> > + backend->size, true, fd, errp);
> > + }
> > +#endif
> > +}
> > +
> > +static void
> > +memfd_backend_class_init(ObjectClass *oc, void *data)
> > +{
> > + HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
> > +
> > + bc->alloc = memfd_backend_memory_alloc;
> > +}
> > +
> > +static const TypeInfo memfd_backend_info = {
> > + .name = TYPE_MEMORY_BACKEND_MEMFD,
> > + .parent = TYPE_MEMORY_BACKEND,
> > + .class_init = memfd_backend_class_init,
> > + .instance_size = sizeof(HostMemoryBackendMemfd),
> > +};
> > +
> > +static void register_types(void)
> > +{
> > + type_register_static(&memfd_backend_info);
> > +}
> > +
> > +type_init(register_types);
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 587de8f..a54af0f 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -3756,6 +3756,18 @@ The @option{share} boolean option determines whether
> > the memory
> > region is marked as private to QEMU, or shared. The latter allows
> > a co-operating external process to access the QEMU memory region.
> >
> > +@item -object memory-backend-memfd,id=@var{id},size=@var{size}
> > +
> > +Creates an anonymous memory file backend object, which can be used to
> > +share the memory with a co-operating external process. The memory is
> > +created with memfd and sealing if possible, but has fallback mechanism
> > +for systems that lack it.
> > +
> > +The @option{id} parameter is a unique ID that will be used to
> > +reference this memory region when configuring the @option{-numa}
> > +argument. The @option{size} option provides the size of the memory
> > +region, and accepts common suffixes, eg @option{500M}.
> > +
> > @item -object rng-random,id=@var{id},filename=@var{/dev/random}
> >
> > Creates a random number generator backend which obtains entropy from
>
>
