[QEMU HCI-8.0 PATCH v4 3/5] vhost-blk: add read-only flag

[Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>]

Also compare BLKROGET with the selected mode and reject r/w if
needed.

https://virtuozzo.atlassian.net/browse/VSTOR-143437
Reviewed-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
---
v2:
 - check BLKROGET only if rw was requested like posix_file

 hw/block/vhost-blk.c          | 25 ++++++++++++++++++++++++-
 include/hw/virtio/vhost-blk.h |  1 +
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/hw/block/vhost-blk.c b/hw/block/vhost-blk.c
index a517c5e22b..dc21f9fbbf 100644
--- a/hw/block/vhost-blk.c
+++ b/hw/block/vhost-blk.c
@@ -234,8 +234,9 @@ static bool vhost_blk_open_backend(VHostBlk *s, Error **errp)
     ERRP_GUARD();
     BlockConf *conf = &s->conf.conf;
     struct stat st;
+    int open_flags = s->conf.readonly ? O_RDONLY : O_RDWR;
 
-    s->backend_fd = qemu_open(s->conf.devpath, O_RDWR, errp);
+    s->backend_fd = qemu_open(s->conf.devpath, open_flags, errp);
     if (s->backend_fd < 0) {
         error_prepend(errp, "vhost-blk: unable to open backend: ");
         return false;
@@ -253,6 +254,23 @@ static bool vhost_blk_open_backend(VHostBlk *s, Error **errp)
         goto fail;
     }
 
+    if (!s->conf.readonly) {
+        int readonly;
+
+        if (ioctl(s->backend_fd, BLKROGET, &readonly) < 0) {
+            error_setg_errno(errp, errno,
+                             "vhost-blk: unable to get read-only status of "
+                             "'%s'", s->conf.devpath);
+            goto fail;
+        }
+
+        if (readonly) {
+            error_setg_errno(errp, EROFS, "vhost-blk: '%s' is not writable",
+                             s->conf.devpath);
+            goto fail;
+        }
+    }
+
     vhost_blk_update_size(s, errp);
     if (*errp) {
         goto fail;
@@ -411,6 +429,10 @@ static uint64_t vhost_blk_get_features(VirtIODevice *vdev,
 
     virtio_add_feature(&features, VIRTIO_F_VERSION_1);
 
+    if (s->conf.readonly) {
+        virtio_add_feature(&features, VIRTIO_BLK_F_RO);
+    }
+
     if (s->conf.num_queues > 1) {
         virtio_add_feature(&features, VIRTIO_BLK_F_MQ);
     }
@@ -458,6 +480,7 @@ static void vhost_blk_update_config(VirtIODevice *vdev, uint8_t *config)
 
 static const Property vhost_blk_properties[] = {
     DEFINE_PROP_STRING("devpath", VHostBlk, conf.devpath),
+    DEFINE_PROP_BOOL("read-only", VHostBlk, conf.readonly, false),
     DEFINE_PROP_UINT16("num-queues", VHostBlk, conf.num_queues,
                        VHOST_BLK_AUTO_NUM_QUEUES),
     DEFINE_PROP_UINT16("queue-size", VHostBlk, conf.queue_size, 256),
diff --git a/include/hw/virtio/vhost-blk.h b/include/hw/virtio/vhost-blk.h
index c194b421d9..c6646f5845 100644
--- a/include/hw/virtio/vhost-blk.h
+++ b/include/hw/virtio/vhost-blk.h
@@ -25,6 +25,7 @@
 typedef struct VhostBlkConf {
     BlockConf conf;
     char *devpath;
+    bool readonly;
     uint16_t num_queues;
     uint16_t queue_size;
     uint16_t num_threads;
-- 
2.43.5