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, 1 insertions, 1 deletions

diff --git a/include/block/raw-aio.h b/include/block/raw-aio.h
index 0e717fd475..8d698ccd31 100644
--- a/include/block/raw-aio.h
+++ b/include/block/raw-aio.h
@@ -43,7 +43,7 @@
 /* linux-aio.c - Linux native implementation */
 #ifdef CONFIG_LINUX_AIO
 typedef struct LinuxAioState LinuxAioState;
-LinuxAioState *laio_init(void);
+LinuxAioState *laio_init(Error **errp);
 void laio_cleanup(LinuxAioState *s);
 int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
                                 uint64_t offset, QEMUIOVector *qiov, int type);