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, 9 insertions, 3 deletions

diff --git a/block/linux-aio.c b/block/linux-aio.c
index 88b8d55ec7..19eb922fdd 100644
--- a/block/linux-aio.c
+++ b/block/linux-aio.c
@@ -15,6 +15,7 @@
 #include "block/raw-aio.h"
 #include "qemu/event_notifier.h"
 #include "qemu/coroutine.h"
+#include "qapi/error.h"
 
 #include <libaio.h>
 
@@ -470,16 +471,21 @@ void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
                            qemu_laio_poll_cb);
 }
 
-LinuxAioState *laio_init(void)
+LinuxAioState *laio_init(Error **errp)
 {
+    int rc;
     LinuxAioState *s;
 
     s = g_malloc0(sizeof(*s));
-    if (event_notifier_init(&s->e, false) < 0) {
+    rc = event_notifier_init(&s->e, false);
+    if (rc < 0) {
+        error_setg_errno(errp, -rc, "failed to to initialize event notifier");
         goto out_free_state;
     }
 
-    if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
+    rc = io_setup(MAX_EVENTS, &s->ctx);
+    if (rc < 0) {
+        error_setg_errno(errp, -rc, "failed to create linux AIO context");
         goto out_close_efd;
     }