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hostmem-file: Add "discard-data" option

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The new option can be used to indicate that the file contents can
be destroyed and don't need to be flushed to disk when QEMU exits
or when the memory backend object is removed.

Internally, it will trigger a madvise(MADV_REMOVE) call when the
memory backend is removed.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170824192315.5897-4-ehabkost@redhat.com>
[ehabkost: fixup: improved documentation]
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Tested-by: Zack Cornelius <zack.cornelius@kove.net>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
This commit is contained in:
Eduardo Habkost 2017-08-24 16:23:15 -03:00
parent 0f81d33530
commit 11ae6ed8af
2 changed files with 36 additions and 1 deletions
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29
backends/hostmem-file.c
View file

@ -32,6 +32,7 @@ struct HostMemoryBackendFile {
HostMemoryBackend parent_obj;
bool share;
bool discard_data;
char *mem_path;
};
@ -103,16 +104,44 @@ static void file_memory_backend_set_share(Object *o, bool value, Error **errp)
fb->share = value;
}
static bool file_memory_backend_get_discard_data(Object *o, Error **errp)
{
return MEMORY_BACKEND_FILE(o)->discard_data;
}
static void file_memory_backend_set_discard_data(Object *o, bool value,
Error **errp)
{
MEMORY_BACKEND_FILE(o)->discard_data = value;
}
static void file_backend_unparent(Object *obj)
{
HostMemoryBackend *backend = MEMORY_BACKEND(obj);
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
if (host_memory_backend_mr_inited(backend) && fb->discard_data) {
void *ptr = memory_region_get_ram_ptr(&backend->mr);
uint64_t sz = memory_region_size(&backend->mr);
qemu_madvise(ptr, sz, QEMU_MADV_REMOVE);
}
}
static void
file_backend_class_init(ObjectClass *oc, void *data)
{
HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
bc->alloc = file_backend_memory_alloc;
oc->unparent = file_backend_unparent;
object_class_property_add_bool(oc, "share",
file_memory_backend_get_share, file_memory_backend_set_share,
&error_abort);
object_class_property_add_bool(oc, "discard-data",
file_memory_backend_get_discard_data, file_memory_backend_set_discard_data,
&error_abort);
object_class_property_add_str(oc, "mem-path",
get_mem_path, set_mem_path,
&error_abort);