block: Add status callback to bdrv_amend_options()

Depending on the changed options and the image format,
bdrv_amend_options() may take a significant amount of time. In these
cases, a way to be informed about the operation's status is desirable.

Since the operation is rather complex and may fundamentally change the
image, implementing it as AIO or a coroutine does not seem feasible. On
the other hand, implementing it as a block job would be significantly
more difficult than a simple callback and would not add benefits other
than progress report to the amending operation, because it should not
actually be run as a block job at all.

A callback may not be very pretty, but it's very easy to implement and
perfectly fits its purpose here.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NBenoît Canet <benoit.canet@nodalink.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Message-id: 1414404776-4919-2-git-send-email-mreitz@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block.c

@@ -5759,12 +5759,13 @@ void bdrv_add_before_write_notifier(BlockDriverState *bs,
     notifier_with_return_list_add(&bs->before_write_notifiers, notifier);
 }
 
-int bdrv_amend_options(BlockDriverState *bs, QemuOpts *opts)
+int bdrv_amend_options(BlockDriverState *bs, QemuOpts *opts,
+                       BlockDriverAmendStatusCB *status_cb)
 {
     if (!bs->drv->bdrv_amend_options) {
         return -ENOTSUP;
     }
-    return bs->drv->bdrv_amend_options(bs, opts);
+    return bs->drv->bdrv_amend_options(bs, opts, status_cb);
 }
 
 /* This function will be called by the bdrv_recurse_is_first_non_filter method

block/qcow2.c

@@ -2613,7 +2613,8 @@ static int qcow2_downgrade(BlockDriverState *bs, int target_version)
     return 0;
 }
 
-static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts)
+static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
+                               BlockDriverAmendStatusCB *status_cb)
 {
     BDRVQcowState *s = bs->opaque;
     int old_version = s->qcow_version, new_version = old_version;

include/block/block.h

@@ -268,7 +268,13 @@ typedef enum {
 
 int bdrv_check(BlockDriverState *bs, BdrvCheckResult *res, BdrvCheckMode fix);
 
-int bdrv_amend_options(BlockDriverState *bs_new, QemuOpts *opts);
+/* The units of offset and total_work_size may be chosen arbitrarily by the
+ * block driver; total_work_size may change during the course of the amendment
+ * operation */
+typedef void BlockDriverAmendStatusCB(BlockDriverState *bs, int64_t offset,
+                                      int64_t total_work_size);
+int bdrv_amend_options(BlockDriverState *bs_new, QemuOpts *opts,
+                       BlockDriverAmendStatusCB *status_cb);
 
 /* external snapshots */
 bool bdrv_recurse_is_first_non_filter(BlockDriverState *bs,

include/block/block_int.h

@@ -232,7 +232,8 @@ struct BlockDriver {
     int (*bdrv_check)(BlockDriverState* bs, BdrvCheckResult *result,
         BdrvCheckMode fix);
 
-    int (*bdrv_amend_options)(BlockDriverState *bs, QemuOpts *opts);
+    int (*bdrv_amend_options)(BlockDriverState *bs, QemuOpts *opts,
+                              BlockDriverAmendStatusCB *status_cb);
 
     void (*bdrv_debug_event)(BlockDriverState *bs, BlkDebugEvent event);
 

qemu-img.c

@@ -2968,7 +2968,7 @@ static int img_amend(int argc, char **argv)
         goto out;
     }
 
-    ret = bdrv_amend_options(bs, opts);
+    ret = bdrv_amend_options(bs, opts, NULL);
     if (ret < 0) {
         error_report("Error while amending options: %s", strerror(-ret));
         goto out;