raw-posix: add Linux native AIO support

Now that do have a nicer interface to work against we can add Linux native
AIO support.  It's an extremly thing layer just setting up an iocb for
the io_submit system call in the submission path, and registering an
eventfd with the qemu poll handler to do complete the iocbs directly
from there.

This started out based on Anthony's earlier AIO patch, but after
estimated 42,000 rewrites and just as many build system changes
there's not much left of it.

To enable native kernel aio use the aio=native sub-command on the
drive command line.  I have also added an option to qemu-io to
test the aio support without needing a guest.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/block.h b/block.h
index ccd4c1e70..28bf35709 100644
--- a/block.h
+++ b/block.h
@@ -37,6 +37,7 @@ typedef struct QEMUSnapshotInfo {
                                      bdrv_file_open()) */
 #define BDRV_O_NOCACHE     0x0020 /* do not use the host page cache */
 #define BDRV_O_CACHE_WB    0x0040 /* use write-back caching */
+#define BDRV_O_NATIVE_AIO  0x0080 /* use native AIO instead of the thread pool */
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB)