virtio_blk: allow read-only disks

Hello Rusty,

sometimes it is useful to share a disk (e.g. usr). To avoid file system
corruption, the disk should be mounted read-only in that case. This patch
adds a new feature flag, that allows the host to specify, if the disk should
be considered read-only.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index c4804f3465db..dd7ea203f940 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -260,6 +260,10 @@ static int virtblk_probe(struct virtio_device *vdev)
         if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))
                 blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_TAG, NULL);
 
+        /* If disk is read-only in the host, the guest should obey */
+        if (virtio_has_feature(vdev, VIRTIO_BLK_F_RO))
+                set_disk_ro(vblk->disk, 1);
+
         /* Host must always specify the capacity. */
         vdev->config->get(vdev, offsetof(struct virtio_blk_config, capacity),
                           &cap, sizeof(cap));
@@ -326,7 +330,7 @@ static struct virtio_device_id id_table[] = {
 
 static unsigned int features[] = {
         VIRTIO_BLK_F_BARRIER, VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX,
-        VIRTIO_BLK_F_GEOMETRY,
+        VIRTIO_BLK_F_GEOMETRY, VIRTIO_BLK_F_RO,
 };
 
 static struct virtio_driver virtio_blk = {