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hostmem-file: add readonly=on|off option

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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.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20210104171320.575838-3-stefanha@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2021-01-04 17:13:19 +00:00 • committed by Eduardo Habkost
parent 369d6dc4de
commit 86635aa4e9
2 changed files with 31 additions and 2 deletions
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28
backends/hostmem-file.c
View file

@ -29,6 +29,7 @@ struct HostMemoryBackendFile {
uint64_t align;
bool discard_data;
bool is_pmem;
bool readonly;
};
static void
@ -56,7 +57,7 @@ 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
}
@ -151,6 +152,28 @@ 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 *obj, Error **errp)
{
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
return fb->readonly;
}
static void file_memory_backend_set_readonly(Object *obj, bool value,
Error **errp)
{
HostMemoryBackend *backend = MEMORY_BACKEND(obj);
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
if (host_memory_backend_mr_inited(backend)) {
error_setg(errp, "cannot change property 'readonly' of %s.",
object_get_typename(obj));
return;
}
fb->readonly = value;
}
static void file_backend_unparent(Object *obj)
{
HostMemoryBackend *backend = MEMORY_BACKEND(obj);
@ -182,6 +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)