Re: [PATCH] machine: add missing doc for memory-backend option

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 14 Jan 2021 20:38:01 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 11/01/21 23:27, Igor Mammedov wrote:
> > Add documentation for '-machine memory-backend' CLI option and
> > how to use it.
> > 
> > PS:
> > While at it add a comment to x-use-canonical-path-for-ramblock-id,
> > to make sure it won't go away by accident.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> >   backends/hostmem.c |  8 ++++++++
> >   qemu-options.hx    | 25 ++++++++++++++++++++++++-
> >   2 files changed, 32 insertions(+), 1 deletion(-)
> > 
> > diff --git a/backends/hostmem.c b/backends/hostmem.c
> > index 4bde00e8e7..f6f4e818c7 100644
> > --- a/backends/hostmem.c
> > +++ b/backends/hostmem.c
> > @@ -497,6 +497,14 @@ host_memory_backend_class_init(ObjectClass *oc, void *data)
> >           host_memory_backend_get_share, host_memory_backend_set_share);
> >       object_class_property_set_description(oc, "share",
> >           "Mark the memory as private to QEMU or shared");
> > +    /*
> > +     * Do not delete/rename option till 4.0 and older machine types exist,
> > +     * Option will be used by upper layers to override (disable) canonical path
> > +     * for ramblock-id set by compat properties on old machine types ( <= 4.0),
> > +     * to keep migration working when backend is used for main RAM with
> > +     * -machine memory-backend= option (main RAM historically used prefix-less
> > +     * ramblock-id).
> > +     */
> >       object_class_property_add_bool(oc, "x-use-canonical-path-for-ramblock-id",
> >           host_memory_backend_get_use_canonical_path,
> >           host_memory_backend_set_use_canonical_path);
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 459c916d3d..c02628bd26 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -35,7 +35,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
> >       "                suppress-vmdesc=on|off disables self-describing migration (default=off)\n"
> >       "                nvdimm=on|off controls NVDIMM support (default=off)\n"
> >       "                memory-encryption=@var{} memory encryption object to use (default=none)\n"
> > -    "                hmat=on|off controls ACPI HMAT support (default=off)\n",
> > +    "                hmat=on|off controls ACPI HMAT support (default=off)\n"
> > +    "                memory-backend='backend-id' specifies explicitly provided backend for main RAM (default=none)\n",
> >       QEMU_ARCH_ALL)
> >   SRST
> >   ``-machine [type=]name[,prop=value[,...]]``
> > @@ -96,6 +97,28 @@ SRST
> >       ``hmat=on|off``
> >           Enables or disables ACPI Heterogeneous Memory Attribute Table
> >           (HMAT) support. The default is off.
> > +
> > +     ``memory-backend='id'``
> > +        An alternative to legacy ``-mem-path`` and ``mem-prealloc`` options.
> > +        Allows to use a memory backend as main RAM.
> > +
> > +        For example:
> > +        ::
> > +        -object memory-backend-file,id=pc.ram,size=512M,mem-path=/hugetlbfs,prealloc=on,share=on
> > +        -machine memory-backend=pc.ram
> > +        -m 512M
> > +
> > +        Migration compatibility note:
> > +        a) as backend id one shall use value of 'default-ram-id', advertised by
> > +        machine type (available via ``query-machines`` QMP command)
> > +        b) for machine types 4.0 and older, user shall
> > +        use ``x-use-canonical-path-for-ramblock-id=on`` backend option,
1) should be
s/on=off/

> > +        if migration to/from old QEMU (<5.0) is expected.
> > +        For example:
> > +        ::
> > +        -object memory-backend-ram,id=pc.ram,size=512M,x-use-canonical-path-for-ramblock-id=on
> > +        -machine memory-backend=pc.ram
> > +        -m 512M
> >   ERST
> >   
> >   HXCOMM Deprecated by -machine
> >   
> 
> Queued, thanks.

Paolo,

can you drop this patch fro your queue, pls?
it has a mistake (1)

v3 is in process of cooking, once there is some agreement I'll post it.

> 
> Paolo
> 
>