[Qemu-block] [PATCH v3 10/10] block: Allow changing 'force-share' on reopen

[Alberto Garcia]

'force-share' is one of the basic BlockdevOptions available for all
drivers, but it's not handled by bdrv_reopen_prepare() so any attempt
to change it results in a "Cannot change the option" error:

   (qemu) qemu-io virtio0 "reopen -o force-share=on"
   Cannot change the option 'force-share'

Since there's no reason why we shouldn't allow changing it and the
implementation is simple let's just do it.

It's worth noting that after this patch the above reopen call will
still return an error -although a different one- if the image is not
read-only:

   (qemu) qemu-io virtio0 "reopen -o force-share=on"
   force-share=on can only be used with read-only images

Signed-off-by: Alberto Garcia <address@hidden>
Reviewed-by: Max Reitz <address@hidden>
---
 block.c               | 30 ++++++++++++++++++++++++------
 include/block/block.h |  1 +
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/block.c b/block.c
index 808411ebf3..57cc4161a2 100644
--- a/block.c
+++ b/block.c
@@ -789,6 +789,18 @@ static BlockdevDetectZeroesOptions 
bdrv_parse_detect_zeroes(QemuOpts *opts,
     return detect_zeroes;
 }
 
+static bool bdrv_parse_force_share(QemuOpts *opts, int flags, Error **errp)
+{
+    bool value = qemu_opt_get_bool_del(opts, BDRV_OPT_FORCE_SHARE, false);
+
+    if (value && (flags & BDRV_O_RDWR)) {
+        error_setg(errp, BDRV_OPT_FORCE_SHARE
+                   "=on can only be used with read-only images");
+    }
+
+    return value;
+}
+
 /**
  * Set open flags for a given discard mode
  *
@@ -1374,12 +1386,9 @@ static int bdrv_open_common(BlockDriverState *bs, 
BlockBackend *file,
     drv = bdrv_find_format(driver_name);
     assert(drv != NULL);
 
-    bs->force_share = qemu_opt_get_bool(opts, BDRV_OPT_FORCE_SHARE, false);
-
-    if (bs->force_share && (bs->open_flags & BDRV_O_RDWR)) {
-        error_setg(errp,
-                   BDRV_OPT_FORCE_SHARE
-                   "=on can only be used with read-only images");
+    bs->force_share = bdrv_parse_force_share(opts, bs->open_flags, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         ret = -EINVAL;
         goto fail_opts;
     }
@@ -3202,6 +3211,14 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, 
BlockReopenQueue *queue,
         goto error;
     }
 
+    reopen_state->force_share =
+        bdrv_parse_force_share(opts, reopen_state->flags, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        ret = -EINVAL;
+        goto error;
+    }
+
     /* All other options (including node-name and driver) must be unchanged.
      * Put them back into the QDict, so that they are checked at the end
      * of this function. */
@@ -3353,6 +3370,7 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
     bs->open_flags         = reopen_state->flags;
     bs->read_only = !(reopen_state->flags & BDRV_O_RDWR);
     bs->detect_zeroes      = reopen_state->detect_zeroes;
+    bs->force_share        = reopen_state->force_share;
 
     /* Remove child references from bs->options and bs->explicit_options.
      * Child options were already removed in bdrv_reopen_queue_child() */
diff --git a/include/block/block.h b/include/block/block.h
index f71fa5a1c4..a49a027c54 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -185,6 +185,7 @@ typedef struct BDRVReopenState {
     BlockDriverState *bs;
     int flags;
     BlockdevDetectZeroesOptions detect_zeroes;
+    bool force_share;
     uint64_t perm, shared_perm;
     QDict *options;
     QDict *explicit_options;
-- 
2.11.0