Let -object memory-backend-file work on read-only files when the
readonly=on option is given. This can be used to share the contents of a
file between multiple guests while preventing them from consuming
Copy-on-Write memory if guests dirty the pages, for example.
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <phi...@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
backends/hostmem-file.c | 26 +++++++++++++++++++++++++-
qemu-options.hx | 5 ++++-
2 files changed, 29 insertions(+), 2 deletions(-)
diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index dffdf142e0..da585e4300 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -31,6 +31,7 @@ struct HostMemoryBackendFile {
uint64_t align;
bool discard_data;
bool is_pmem;
+ bool readonly;
};
static void
@@ -58,7 +59,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error
**errp)
backend->size, fb->align,
(backend->share ? RAM_SHARED : 0) |
(fb->is_pmem ? RAM_PMEM : 0),
- fb->mem_path, false, errp);
+ fb->mem_path, fb->readonly, errp);
g_free(name);
#endif
}
@@ -153,6 +154,26 @@ static void file_memory_backend_set_pmem(Object *o, bool
value, Error **errp)
fb->is_pmem = value;
}
+static bool file_memory_backend_get_readonly(Object *o, Error **errp)
+{
+ return MEMORY_BACKEND_FILE(o)->readonly;
+}
+
+static void file_memory_backend_set_readonly(Object *o, bool value,
+ Error **errp)
+{
+ HostMemoryBackend *backend = MEMORY_BACKEND(o);
+ HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+
+ if (host_memory_backend_mr_inited(backend)) {
+ error_setg(errp, "cannot change property 'readonly' of %s.",
+ object_get_typename(o));
+ return;
+ }
+
+ fb->readonly = value;
+}
+
static void file_backend_unparent(Object *obj)
{
HostMemoryBackend *backend = MEMORY_BACKEND(obj);
@@ -184,6 +205,9 @@ file_backend_class_init(ObjectClass *oc, void *data)
NULL, NULL);
object_class_property_add_bool(oc, "pmem",
file_memory_backend_get_pmem, file_memory_backend_set_pmem);
+ object_class_property_add_bool(oc, "readonly",
+ file_memory_backend_get_readonly,
+ file_memory_backend_set_readonly);
}
static void file_backend_instance_finalize(Object *o)
diff --git a/qemu-options.hx b/qemu-options.hx
index b0f020594e..3dfaaddd62 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4369,7 +4369,7 @@ SRST
they are specified. Note that the 'id' property must be set. These
objects are placed in the '/objects' path.
- ``-object
memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align``
+ ``-object
memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,readonly=on|off``
Creates a memory file backend object, which can be used to back
the guest RAM with huge pages.
@@ -4452,6 +4452,9 @@ SRST
4.15) and the filesystem of ``mem-path`` mounted with DAX
option.
+ The ``readonly`` option specifies whether the backing file is opened
+ read-only or read-write (default).
+
``-object
memory-backend-ram,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave``
Creates a memory backend object, which can be used to back the
guest RAM. Memory backend objects offer more control than the
--
2.26.2
