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>
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@ -713,6 +713,12 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
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*/
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fd = qemu_open(path, O_RDWR, NULL);
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if (fd < 0) {
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/*
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* qemu_open() can fail if the user specifies a path that is not
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* a file or device, for example in the case of Unix Domain Socket
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* for the virtio-blk-vhost-user driver. In such cases let's have
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* libblkio open the path directly.
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*/
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fd_supported = false;
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} else {
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ret = blkio_set_int(s->blkio, "fd", fd);
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@ -741,9 +747,12 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
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}
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/*
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* If the libblkio driver doesn't support the `fd` property, blkio_connect()
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* will fail with -EINVAL. So let's try calling blkio_connect() again by
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* directly setting `path`.
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* Before https://gitlab.com/libblkio/libblkio/-/merge_requests/208
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* (libblkio <= v1.3.0), setting the `fd` property is not enough to check
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* whether the driver supports the `fd` property or not. In that case,
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* blkio_connect() will fail with -EINVAL.
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* So let's try calling blkio_connect() again by directly setting `path`
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* to cover this scenario.
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*/
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if (fd_supported && ret == -EINVAL) {
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/*
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