linux-aio: properly bubble up errors from initialization

laio_init() can fail for a couple of reasons, which will lead to a NULL
pointer dereference in laio_attach_aio_context().

To solve this, add a aio_setup_linux_aio() function which is called
early in raw_open_common. If this fails, propagate the error up. The
signature of aio_get_linux_aio() was not modified, because it seems
preferable to return the actual errno from the possible failing
initialization calls.

Additionally, when the AioContext changes, we need to associate a
LinuxAioState with the new AioContext. Use the bdrv_attach_aio_context
callback and call the new aio_setup_linux_aio(), which will allocate a
new AioContext if needed, and return errors on failures. If it fails for
any reason, fallback to threaded AIO with an error message, as the
device is already in-use by the guest.

Add an assert that aio_get_linux_aio() cannot return NULL.

Signed-off-by: Nishanth Aravamudan <naravamudan@digitalocean.com>
Message-id: 20180622193700.6523-1-naravamudan@digitalocean.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 28 insertions, 5 deletions

diff --git a/block/file-posix.c b/block/file-posix.c
index 07bb061..43b963b 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -545,11 +545,17 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
 
 #ifdef CONFIG_LINUX_AIO
      /* Currently Linux does AIO only for files opened with O_DIRECT */
-    if (s->use_linux_aio && !(s->open_flags & O_DIRECT)) {
-        error_setg(errp, "aio=native was specified, but it requires "
-                         "cache.direct=on, which was not specified.");
-        ret = -EINVAL;
-        goto fail;
+    if (s->use_linux_aio) {
+        if (!(s->open_flags & O_DIRECT)) {
+            error_setg(errp, "aio=native was specified, but it requires "
+                             "cache.direct=on, which was not specified.");
+            ret = -EINVAL;
+            goto fail;
+        }
+        if (!aio_setup_linux_aio(bdrv_get_aio_context(bs), errp)) {
+            error_prepend(errp, "Unable to use native AIO: ");
+            goto fail;
+        }
     }
 #else
     if (s->use_linux_aio) {
@@ -1723,6 +1729,22 @@ static BlockAIOCB *raw_aio_flush(BlockDriverState *bs,
     return paio_submit(bs, s->fd, 0, NULL, 0, cb, opaque, QEMU_AIO_FLUSH);
 }
 
+static void raw_aio_attach_aio_context(BlockDriverState *bs,
+                                       AioContext *new_context)
+{
+#ifdef CONFIG_LINUX_AIO
+    BDRVRawState *s = bs->opaque;
+    if (s->use_linux_aio) {
+        Error *local_err;
+        if (!aio_setup_linux_aio(new_context, &local_err)) {
+            error_reportf_err(local_err, "Unable to use native AIO, "
+                                         "falling back to thread pool: ");
+            s->use_linux_aio = false;
+        }
+    }
+#endif
+}
+
 static void raw_close(BlockDriverState *bs)
 {
     BDRVRawState *s = bs->opaque;
@@ -2601,6 +2623,7 @@ BlockDriver bdrv_file = {
     .bdrv_refresh_limits = raw_refresh_limits,
     .bdrv_io_plug = raw_aio_plug,
     .bdrv_io_unplug = raw_aio_unplug,
+    .bdrv_attach_aio_context = raw_aio_attach_aio_context,
 
     .bdrv_truncate = raw_truncate,
     .bdrv_getlength = raw_getlength,