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block/blkio: add more comments on the fd passing handling 

As Hanna pointed out, it is not clear in the code why qemu_open()
can fail, and why blkio_set_int("fd") is not enough to discover
the `fd` property support.

Let's fix them by adding more details in the code comments.

Suggested-by: Hanna Czenczek <hreitz@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20230803082825.25293-3-sgarzare@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefano Garzarella 2023-08-03 10:28:25 +02:00 committed by Stefan Hajnoczi
parent 0b054b4c82
commit 9b06d0d076
1 changed files with 12 additions and 3 deletions
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15
block/blkio.c
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@ -713,6 +713,12 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
*/
fd = qemu_open(path, O_RDWR, NULL);
if (fd < 0) {
/*
* qemu_open() can fail if the user specifies a path that is not
* a file or device, for example in the case of Unix Domain Socket
* for the virtio-blk-vhost-user driver. In such cases let's have
* libblkio open the path directly.
*/
fd_supported = false;
} else {
ret = blkio_set_int(s->blkio, "fd", fd);
@ -741,9 +747,12 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
}
/*
* If the libblkio driver doesn't support the `fd` property, blkio_connect()
* will fail with -EINVAL. So let's try calling blkio_connect() again by
* directly setting `path`.
* Before https://gitlab.com/libblkio/libblkio/-/merge_requests/208
* (libblkio <= v1.3.0), setting the `fd` property is not enough to check
* whether the driver supports the `fd` property or not. In that case,
* blkio_connect() will fail with -EINVAL.
* So let's try calling blkio_connect() again by directly setting `path`
* to cover this scenario.
*/
if (fd_supported && ret == -EINVAL) {
/*