On Mon, 18 Feb 2019 13:06:55 +0000
Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx> wrote:
> Since we don't currently tell the guest when the disk backend is
> read-only, it will report any inconsistent read after write as an error.
> An image may be read-only either because user requested it on the
> command-line, or because write support isn't implemented. Pass the
> read-only attribute using the VIRTIO_BLK_F_RO feature.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>
Cheers,
Andre
> ---
> disk/core.c | 9 +++++++--
> include/kvm/disk-image.h | 1 +
> virtio/blk.c | 5 ++++-
> 3 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/disk/core.c b/disk/core.c
> index dd2f258b0..4c7c4f030 100644
> --- a/disk/core.c
> +++ b/disk/core.c
> @@ -139,8 +139,10 @@ static struct disk_image *disk_image__open(const char *filename, bool readonly,
>
> /* blk device ?*/
> disk = blkdev__probe(filename, flags, &st);
> - if (!IS_ERR_OR_NULL(disk))
> + if (!IS_ERR_OR_NULL(disk)) {
> + disk->readonly = readonly;
> return disk;
> + }
>
> fd = open(filename, flags);
> if (fd < 0)
> @@ -150,13 +152,16 @@ static struct disk_image *disk_image__open(const char *filename, bool readonly,
> disk = qcow_probe(fd, true);
> if (!IS_ERR_OR_NULL(disk)) {
> pr_warning("Forcing read-only support for QCOW");
> + disk->readonly = true;
> return disk;
> }
>
> /* raw image ?*/
> disk = raw_image__probe(fd, &st, readonly);
> - if (!IS_ERR_OR_NULL(disk))
> + if (!IS_ERR_OR_NULL(disk)) {
> + disk->readonly = readonly;
> return disk;
> + }
>
> if (close(fd) < 0)
> pr_warning("close() failed");
> diff --git a/include/kvm/disk-image.h b/include/kvm/disk-image.h
> index b72805242..4746e88c9 100644
> --- a/include/kvm/disk-image.h
> +++ b/include/kvm/disk-image.h
> @@ -59,6 +59,7 @@ struct disk_image {
> void *priv;
> void *disk_req_cb_param;
> void (*disk_req_cb)(void *param, long len);
> + bool readonly;
> bool async;
> int evt;
> #ifdef CONFIG_HAS_AIO
> diff --git a/virtio/blk.c b/virtio/blk.c
> index a57df2e96..6e7a1ee36 100644
> --- a/virtio/blk.c
> +++ b/virtio/blk.c
> @@ -148,10 +148,13 @@ static u8 *get_config(struct kvm *kvm, void *dev)
>
> static u32 get_host_features(struct kvm *kvm, void *dev)
> {
> + struct blk_dev *bdev = dev;
> +
> return 1UL << VIRTIO_BLK_F_SEG_MAX
> | 1UL << VIRTIO_BLK_F_FLUSH
> | 1UL << VIRTIO_RING_F_EVENT_IDX
> - | 1UL << VIRTIO_RING_F_INDIRECT_DESC;
> + | 1UL << VIRTIO_RING_F_INDIRECT_DESC
> + | (bdev->disk->readonly ? 1UL << VIRTIO_BLK_F_RO : 0);
> }
>
> static void set_guest_features(struct kvm *kvm, void *dev, u32 features)
