backends/hostmem-shm: factor out allocation of "anonymous shared memory with an fd"

Let's factor it out so we can reuse it.

Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-2-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>

1 files changed, 4 insertions, 41 deletions

diff --git a/backends/hostmem-shm.c b/backends/hostmem-shm.c
index 5551ba7..fabee41 100644
--- a/backends/hostmem-shm.c
+++ b/backends/hostmem-shm.c
@@ -25,11 +25,9 @@ struct HostMemoryBackendShm {
 static bool
 shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 {
-    g_autoptr(GString) shm_name = g_string_new(NULL);
     g_autofree char *backend_name = NULL;
     uint32_t ram_flags;
-    int fd, oflag;
-    mode_t mode;
+    int fd;
 
     if (!backend->size) {
         error_setg(errp, "can't create shm backend with size 0");
@@ -41,48 +39,13 @@ shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         return false;
     }
 
-    /*
-     * Let's use `mode = 0` because we don't want other processes to open our
-     * memory unless we share the file descriptor with them.
-     */
-    mode = 0;
-    oflag = O_RDWR | O_CREAT | O_EXCL;
-    backend_name = host_memory_backend_get_name(backend);
-
-    /*
-     * Some operating systems allow creating anonymous POSIX shared memory
-     * objects (e.g. FreeBSD provides the SHM_ANON constant), but this is not
-     * defined by POSIX, so let's create a unique name.
-     *
-     * From Linux's shm_open(3) man-page:
-     *   For  portable  use,  a shared  memory  object should be identified
-     *   by a name of the form /somename;"
-     */
-    g_string_printf(shm_name, "/qemu-" FMT_pid "-shm-%s", getpid(),
-                    backend_name);
-
-    fd = shm_open(shm_name->str, oflag, mode);
+    fd = qemu_shm_alloc(backend->size, errp);
     if (fd < 0) {
-        error_setg_errno(errp, errno,
-                         "failed to create POSIX shared memory");
-        return false;
-    }
-
-    /*
-     * We have the file descriptor, so we no longer need to expose the
-     * POSIX shared memory object. However it will remain allocated as long as
-     * there are file descriptors pointing to it.
-     */
-    shm_unlink(shm_name->str);
-
-    if (ftruncate(fd, backend->size) == -1) {
-        error_setg_errno(errp, errno,
-                         "failed to resize POSIX shared memory to %" PRIu64,
-                         backend->size);
-        close(fd);
         return false;
     }
 
+    /* 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;