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 <[email protected]>
Reviewed-by: Alberto Garcia <[email protected]>
Message-id: 20190201192935[email protected]
Signed-off-by: Max Reitz <[email protected]>

diff --git a/block.c b/block.c
index d14ce1c98cd0eca19febd47f12818839b22c2b41..9f655c0fd6444f0e250be9f97c0a80fc43601a43 100644 (file)
--- 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

diff --git a/include/block/block.h b/include/block/block.h
index 42cc38f598a92f937cb0cce31523854338d05362..5b5cf868df093206562123d94e73c0dec4e87840 100644 (file)
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -491,6 +491,7 @@ char *bdrv_get_full_backing_filename(BlockDriverState *bs, Error **errp);
 char *bdrv_get_full_backing_filename_from_filename(const char *backed,
                                                    const char *backing,
                                                    Error **errp);
+char *bdrv_dirname(BlockDriverState *bs, Error **errp);
 
 int path_has_protocol(const char *path);
 int path_is_absolute(const char *path);

diff --git a/include/block/block_int.h b/include/block/block_int.h
index dd7276cde23246dbf20b3e1b790c305eee4980c0..e4d4817ea6ff80eb51585cfa4d910f2cb0289ad2 100644 (file)
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -141,6 +141,13 @@ struct BlockDriver {
 
     void (*bdrv_refresh_filename)(BlockDriverState *bs, QDict *options);
 
+    /*
+     * Returns an allocated string which is the directory name of this BDS: It
+     * will be used to make relative filenames absolute by prepending this
+     * function's return value to them.
+     */
+    char *(*bdrv_dirname)(BlockDriverState *bs, Error **errp);
+
     /* aio */
     BlockAIOCB *(*bdrv_aio_preadv)(BlockDriverState *bs,
         uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags,