block: Framework for reopening files safely

This is based on Supriya Kannery's bdrv_reopen() patch series.

This provides a transactional method to reopen multiple
images files safely.

Image files are queue for reopen via bdrv_reopen_queue(), and the
reopen occurs when bdrv_reopen_multiple() is called.  Changes are
staged in bdrv_reopen_prepare() and in the equivalent driver level
functions.  If any of the staged images fails a prepare, then all
of the images left untouched, and the staged changes for each image
abandoned.

Block drivers are passed a reopen state structure, that contains:
    * BDS to reopen
    * flags for the reopen
    * opaque pointer for any driver-specific data that needs to be
      persistent from _prepare to _commit/_abort
    * reopen queue pointer, if the driver needs to queue additional
      BDS for a reopen

Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/block_int.h b/block_int.h
index 4452f6f398..22b3d93d19 100644
--- a/block_int.h
+++ b/block_int.h
@@ -139,6 +139,13 @@ struct BlockDriver {
     int instance_size;
     int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
     int (*bdrv_probe_device)(const char *filename);
+
+    /* For handling image reopen for split or non-split files */
+    int (*bdrv_reopen_prepare)(BDRVReopenState *reopen_state,
+                               BlockReopenQueue *queue, Error **errp);
+    void (*bdrv_reopen_commit)(BDRVReopenState *reopen_state);
+    void (*bdrv_reopen_abort)(BDRVReopenState *reopen_state);
+
     int (*bdrv_open)(BlockDriverState *bs, int flags);
     int (*bdrv_file_open)(BlockDriverState *bs, const char *filename, int flags);
     int (*bdrv_read)(BlockDriverState *bs, int64_t sector_num,
@@ -336,6 +343,7 @@ struct BlockDriverState {
 
     /* long-running background operation */
     BlockJob *job;
+
 };
 
 int get_tmp_filename(char *filename, int size);