block: Add bdrv_dirname()

This function may be implemented by block drivers to derive a directory
name from a BDS. Concatenating this g_free()-able string with a relative
filename must result in a valid (not necessarily existing) filename, so
this is a function that should generally be not implemented by format
drivers, because this is protocol-specific.

If a BDS's driver does not implement this function, bdrv_dirname() will
fall through to the BDS's file if it exists. If it does not, the
exact_filename field will be used to generate a directory name.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20190201192935.18394-15-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/block.c b/block.c
index d14ce1c98c..9f655c0fd6 100644
--- a/block.c
+++ b/block.c
@@ -5715,6 +5715,33 @@ void bdrv_refresh_filename(BlockDriverState *bs)
     }
 }
 
+char *bdrv_dirname(BlockDriverState *bs, Error **errp)
+{
+    BlockDriver *drv = bs->drv;
+
+    if (!drv) {
+        error_setg(errp, "Node '%s' is ejected", bs->node_name);
+        return NULL;
+    }
+
+    if (drv->bdrv_dirname) {
+        return drv->bdrv_dirname(bs, errp);
+    }
+
+    if (bs->file) {
+        return bdrv_dirname(bs->file->bs, errp);
+    }
+
+    bdrv_refresh_filename(bs);
+    if (bs->exact_filename[0] != '\0') {
+        return path_combine(bs->exact_filename, "");
+    }
+
+    error_setg(errp, "Cannot generate a base directory for %s nodes",
+               drv->format_name);
+    return NULL;
+}
+
 /*
  * Hot add/remove a BDS's child. So the user can take a child offline when
  * it is broken and take a new child online