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[PATCH v3] machine: add missing doc for memory-backend option
From: |
Igor Mammedov |
Subject: |
[PATCH v3] machine: add missing doc for memory-backend option |
Date: |
Thu, 21 Jan 2021 11:15:04 -0500 |
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>
---
v2:
- add doc that x-use-canonical-path-for-ramblock-id is considered stable,
(Peter Krempa <pkrempa@redhat.com>)
v3:
-
s/x-use-canonical-path-for-ramblock-id=on/x-use-canonical-path-for-ramblock-id=off/
(Michal Privoznik <mprivozn@redhat.com>)
- add to commit message why x- prefix is preserved
- drop clause about x-use-canonical-path-for-ramblock-id being stable
from help section, but keep it in code comment above
x-use-canonical-path-for-ramblock-id property. It's sufficient
to prevent option being changed/removed by accident.
(Peter Maydell <peter.maydell@linaro.org>)
---
backends/hostmem.c | 10 ++++++++++
qemu-options.hx | 26 +++++++++++++++++++++++++-
2 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/backends/hostmem.c b/backends/hostmem.c
index 9f9ac95edd..813aeb83c9 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -498,6 +498,16 @@ 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. This option must be considered stable
+ * (as if it didn't have the 'x-' prefix including deprecation period) as
+ * long as 4.0 and older machine types exists.
+ * 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 62791f56d8..059b1a1d14 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 +97,29 @@ 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), 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
--
2.27.0
- [PATCH v3] machine: add missing doc for memory-backend option,
Igor Mammedov <=
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Michal Privoznik, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Daniel P . Berrangé, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Daniel P . Berrangé, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Michal Privoznik, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Daniel P . Berrangé, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Igor Mammedov, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Michal Privoznik, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Igor Mammedov, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Daniel P . Berrangé, 2021/01/27
- Re: [PATCH v3] machine: add missing doc for memory-backend option, Michal Privoznik, 2021/01/27