[Qemu-devel] [PATCH] blockdev: warn about aio=native if libaio is unavailable

[Stefan Hajnoczi <stefanha@redhat.com>]

QEMU silently ignores aio=native if libaio is unavailable.  It is
confusing when aio=native performance is identical to aio=threads
because the binary was accidentally built without libaio.

Use error_report() because failing would break backward compatibility.
There are probably users using aio=native who would be inconvenienced if
QEMU suddenly refused to start their guests.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 blockdev.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 62a4586..f30828a 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -405,10 +405,14 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
         bdrv_flags |= BDRV_O_NO_FLUSH;
     }
 
-#ifdef CONFIG_LINUX_AIO
     if ((buf = qemu_opt_get(opts, "aio")) != NULL) {
         if (!strcmp(buf, "native")) {
+#ifdef CONFIG_LINUX_AIO
             bdrv_flags |= BDRV_O_NATIVE_AIO;
+#else
+            error_report("warning: aio=native support unavailable, "
+                         "using default instead");
+#endif
         } else if (!strcmp(buf, "threads")) {
             /* this is the default */
         } else {
@@ -416,7 +420,6 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
            goto early_err;
         }
     }
-#endif
 
     if ((buf = qemu_opt_get(opts, "format")) != NULL) {
         if (is_help_option(buf)) {
-- 
2.4.3