machine: add missing doc for memory-backend option
Add documentation for '-machine memory-backend' CLI option and
how to use it.
And document that x-use-canonical-path-for-ramblock-id,
is considered to be stable to make sure it won't go away by accident.
x- was intended for unstable/iternal properties, and not supposed to
be stable option. However it's too late to rename (drop x-)
it as it would mean that users will have to mantain both
x-use-canonical-path-for-ramblock-id (for QEMU 5.0-5.2) versions
and prefix-less for later versions.
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20210121161504.1007247-1-imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/qemu-options.hx b/qemu-options.hx
index c09c464..6c34c70 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -35,7 +35,8 @@
" 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 +97,29 @@
``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), if migration
+ to/from old QEMU (<5.0) is expected.
+ b) for machine types 4.0 and older, user shall
+ use ``x-use-canonical-path-for-ramblock-id=off`` backend option
+ 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=off
+ -machine memory-backend=pc.ram
+ -m 512M
ERST
HXCOMM Deprecated by -machine
