block: Add bdrv_refresh_filename()

Some block devices may not have a filename in their BDS; and for some,
there may not even be a normal filename at all. To work around this, add
a function which tries to construct a valid filename for the
BDS.filename field.

If a filename exists or a block driver is able to reconstruct a valid
filename (which is placed in BDS.exact_filename), this can directly be
used.

If no filename can be constructed, we can still construct an options
QDict which is then converted to a JSON object and prefixed with the
"json:" pseudo protocol prefix. The QDict is placed in
BDS.full_open_options.

For most block drivers, this process can be done automatically; those
that need special handling may define a .bdrv_refresh_filename() method
to fill BDS.exact_filename and BDS.full_open_options themselves.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 7 insertions, 0 deletions

diff --git a/include/block/block.h b/include/block/block.h
index e94b701667..8f4ad16d8f 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -274,6 +274,7 @@ int coroutine_fn bdrv_co_write_zeroes(BlockDriverState *bs, int64_t sector_num,
 BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
     const char *backing_file);
 int bdrv_get_backing_file_depth(BlockDriverState *bs);
+void bdrv_refresh_filename(BlockDriverState *bs);
 int bdrv_truncate(BlockDriverState *bs, int64_t offset);
 int64_t bdrv_nb_sectors(BlockDriverState *bs);
 int64_t bdrv_getlength(BlockDriverState *bs);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 7b541a0691..233489547e 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -123,6 +123,9 @@ struct BlockDriver {
     int (*bdrv_create)(const char *filename, QemuOpts *opts, Error **errp);
     int (*bdrv_set_key)(BlockDriverState *bs, const char *key);
     int (*bdrv_make_empty)(BlockDriverState *bs);
+
+    void (*bdrv_refresh_filename)(BlockDriverState *bs);
+
     /* aio */
     BlockDriverAIOCB *(*bdrv_aio_readv)(BlockDriverState *bs,
         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
@@ -323,6 +326,9 @@ struct BlockDriverState {
                                 this file image */
     char backing_format[16]; /* if non-zero and backing_file exists */
 
+    QDict *full_open_options;
+    char exact_filename[1024];
+
     BlockDriverState *backing_hd;
     BlockDriverState *file;