hostmem-shm: preserve for cpr

Preserve memory-backend-shm memory objects during cpr-transfer.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-11-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>

backends/hostmem-shm.c

@@ -13,6 +13,7 @@
 #include "qemu/osdep.h"
 #include "system/hostmem.h"
 #include "qapi/error.h"
+#include "migration/cpr.h"
 
 #define TYPE_MEMORY_BACKEND_SHM "memory-backend-shm"
 
@@ -25,9 +26,9 @@ struct HostMemoryBackendShm {
 static bool
 shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 {
-    g_autofree char *backend_name = NULL;
+    g_autofree char *backend_name = host_memory_backend_get_name(backend);
     uint32_t ram_flags;
-    int fd;
+    int fd = cpr_find_fd(backend_name, 0);
 
     if (!backend->size) {
         error_setg(errp, "can't create shm backend with size 0");
@@ -39,13 +40,18 @@ shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         return false;
     }
 
+    if (fd >= 0) {
+        goto have_fd;
+    }
+
     fd = qemu_shm_alloc(backend->size, errp);
     if (fd < 0) {
         return false;
     }
+    cpr_save_fd(backend_name, 0, fd);
 
+have_fd:
     /* Let's do the same as memory-backend-ram,share=on would do. */
-    backend_name = host_memory_backend_get_name(backend);
     ram_flags = RAM_SHARED;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;