Laurent Vivier <lviv...@redhat.com> writes: > On 10/05/2019 14:27, Markus Armbruster wrote: >> Laurent Vivier <lviv...@redhat.com> writes: >> >>> Add a new RNG backend using QEMU builtin getrandom function. >>> >>> It can be created and used with something like: >>> >>> ... -object rng-builtin,id=rng0 -device virtio-rng,rng=rng0 ... >>> >>> Reviewed-by: Richard Henderson <richard.hender...@linaro.org> >>> Signed-off-by: Laurent Vivier <lviv...@redhat.com> >>> --- >>> >>> Notes: >>> This patch applies on top of >>> "[PATCH v5 00/24] Add qemu_getrandom and ARMv8.5-RNG etc" >>> Based-on: 20190510012458.22706-1-richard.hender...@linaro.org >>> v2: Update qemu-options.hx >>> describe the new backend and specify virtio-rng uses the >>> rng-random by default (do we want to change this?) >>> >>> backends/Makefile.objs | 2 +- >>> backends/rng-builtin.c | 56 ++++++++++++++++++++++++++++++++++++++++++ >>> qemu-options.hx | 10 +++++++- >>> 3 files changed, 66 insertions(+), 2 deletions(-) >>> create mode 100644 backends/rng-builtin.c >>> >>> diff --git a/backends/Makefile.objs b/backends/Makefile.objs >>> index ff619d31b461..8da4a508d97b 100644 >>> --- a/backends/Makefile.objs >>> +++ b/backends/Makefile.objs >>> @@ -1,4 +1,4 @@ >>> -common-obj-y += rng.o rng-egd.o >>> +common-obj-y += rng.o rng-egd.o rng-builtin.o >>> common-obj-$(CONFIG_POSIX) += rng-random.o >>> common-obj-$(CONFIG_TPM) += tpm.o >>> diff --git a/backends/rng-builtin.c b/backends/rng-builtin.c >>> new file mode 100644 >>> index 000000000000..b1264b745407 >>> --- /dev/null >>> +++ b/backends/rng-builtin.c >>> @@ -0,0 +1,56 @@ >>> +/* >>> + * QEMU Builtin Random Number Generator Backend >>> + * >>> + * 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 "sysemu/rng.h" >>> +#include "qapi/error.h" >>> +#include "qapi/qmp/qerror.h" >>> +#include "qemu/main-loop.h" >>> +#include "qemu/guest-random.h" >>> + >>> +#define TYPE_RNG_BUILTIN "rng-builtin" >>> +#define RNG_BUILTIN(obj) OBJECT_CHECK(RngBuiltin, (obj), TYPE_RNG_BUILTIN) >>> + >>> +typedef struct RngBuiltin { >>> + RngBackend parent; >>> +} RngBuiltin; >>> + >>> +static void rng_builtin_request_entropy(RngBackend *b, RngRequest *req) >>> +{ >>> + RngBuiltin *s = RNG_BUILTIN(b); >>> + >>> + while (!QSIMPLEQ_EMPTY(&s->parent.requests)) { >>> + RngRequest *req = QSIMPLEQ_FIRST(&s->parent.requests); >>> + >>> + qemu_guest_getrandom_nofail(req->data, req->size); >>> + >>> + req->receive_entropy(req->opaque, req->data, req->size); >>> + >>> + rng_backend_finalize_request(&s->parent, req); >>> + } >>> +} >>> + >>> +static void rng_builtin_class_init(ObjectClass *klass, void *data) >>> +{ >>> + RngBackendClass *rbc = RNG_BACKEND_CLASS(klass); >>> + >>> + rbc->request_entropy = rng_builtin_request_entropy; >>> +} >>> + >>> +static const TypeInfo rng_builtin_info = { >>> + .name = TYPE_RNG_BUILTIN, >>> + .parent = TYPE_RNG_BACKEND, >>> + .instance_size = sizeof(RngBuiltin), >>> + .class_init = rng_builtin_class_init, >>> +}; >>> + >>> +static void register_types(void) >>> +{ >>> + type_register_static(&rng_builtin_info); >>> +} >>> + >>> +type_init(register_types); >>> diff --git a/qemu-options.hx b/qemu-options.hx >>> index 0191ef8b1eb7..3e2a51c691b0 100644 >>> --- a/qemu-options.hx >>> +++ b/qemu-options.hx >>> @@ -4280,13 +4280,21 @@ other options. >>> The @option{share} boolean option is @var{on} by default with >>> memfd. >>> +@item -object rng-builtin,id=@var{id} >>> + >>> +Creates a random number generator backend which obtains entropy from >>> +QEMU builtin functions. The @option{id} parameter is a unique ID that >>> +will be used to reference this entropy backend from the @option{virtio-rng} >>> +device. >>> + >>> @item -object rng-random,id=@var{id},filename=@var{/dev/random} >>> Creates a random number generator backend which obtains entropy >>> from >>> a device on the host. The @option{id} parameter is a unique ID that >>> will be used to reference this entropy backend from the >>> @option{virtio-rng} >>> device. >> >> There's also the "spapr-rng" device, I think. > > spapr-rng doesn't have default. You must specify one to be able to use it: > qemu-system-ppc64: -device spapr-rng: spapr-rng needs an RNG backend!
You're right. >>> The @option{filename} parameter specifies which file to obtain >>> -entropy from and if omitted defaults to @option{/dev/random}. >>> +entropy from and if omitted defaults to @option{/dev/random}. By default, >>> +the @option{virtio-rng} device uses this RNG backend. >>> @item -object rng-egd,id=@var{id},chardev=@var{chardevid} >> >> Trivial conflict with Kashyap's "[PATCH v2] VirtIO-RNG: Update default >> entropy source to `/dev/urandom`". >> >> virtio-rng indeed creates an rng-random backend when the user doesn't >> specify one. I consider having device model frontends create backends a >> bad idea. Not this patch's fault, of course. >> >> That said, would rng-builtin be a better default? For starters, it's >> available when !CONFIG_POSIX. I suspect virtio-rng crashes when it >> tries to create an rng-random that isn't available. > > I will send a v3 with rng-builtin as a default. Maintainer will be > able to pick one of his choice, v2 or v3. > >> >> The new rng-builtin is considerably simpler than both rng-random and >> rng-egd. Moreover, it just works, whereas rng-random is limited to >> CONFIG_POSIX, and rng-egd needs egd running (which I suspect basically >> nobody does). Have we considered deprecating these two backends in >> favor of rng-builtin? > > I have several bugzilla involving these backends: as there are > blocking, the virtio-rng device in the guest can hang, or crash during > hot-unplug. From my point of view, life would be easier without > them... Sounds like perfectly fine reasons for deprecating them. Amit, what do you think?