[Qemu-block] [PATCH 18/19] block: Add 'base-directory' BDS option

[Max Reitz]

Using this option, one can directly override what bdrv_dirname() will
return. This is useful if one uses e.g. qcow2 on top of quorum (with
only protocol BDSs under the quorum BDS) and wants to be able to use
relative backing filenames.

Signed-off-by: Max Reitz <address@hidden>
---
 block.c                   | 13 +++++++++++++
 include/block/block_int.h |  2 ++
 qapi/block-core.json      |  9 +++++++++
 3 files changed, 24 insertions(+)

diff --git a/block.c b/block.c
index a909b7a..2086c6d 100644
--- a/block.c
+++ b/block.c
@@ -889,6 +889,11 @@ static QemuOptsList bdrv_runtime_opts = {
             .type = QEMU_OPT_BOOL,
             .help = "Ignore flush requests",
         },
+        {
+            .name = "base-directory",
+            .type = QEMU_OPT_STRING,
+            .help = "String to be prepended to filenames relative to this BDS 
to make them absolute",
+        },
         { /* end of list */ }
     },
 };
@@ -948,6 +953,8 @@ static int bdrv_open_common(BlockDriverState *bs, BdrvChild 
*file,
         goto fail_opts;
     }
 
+    bs->dirname = g_strdup(qemu_opt_get(opts, "base-directory"));
+
     bs->request_alignment = 512;
     bs->zero_beyond_eof = true;
     bs->read_only = !(bs->open_flags & BDRV_O_RDWR);
@@ -2359,6 +2366,8 @@ static void bdrv_delete(BlockDriverState *bs)
 
     bdrv_close(bs);
 
+    g_free(bs->dirname);
+
     /* remove from list, if necessary */
     if (bs->node_name[0] != '\0') {
         QTAILQ_REMOVE(&graph_bdrv_states, bs, node_list);
@@ -4043,6 +4052,10 @@ char *bdrv_dirname(BlockDriverState *bs, Error **errp)
 {
     BlockDriver *drv = bs->drv;
 
+    if (bs->dirname) {
+        return g_strdup(bs->dirname);
+    }
+
     if (!drv) {
         error_setg(errp, "Node '%s' is ejected", bs->node_name);
         return NULL;
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 087d9ac..863caf2 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -415,6 +415,8 @@ struct BlockDriverState {
     QDict *full_open_options;
     char exact_filename[PATH_MAX];
 
+    char *dirname;
+
     BdrvChild *backing;
     BdrvChild *file;
 
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 1d09079..85b8e06 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2045,6 +2045,14 @@
 # @node-name:     #optional the name of a block driver state node (Since 2.0).
 #                 This option is required on the top level of blockdev-add if
 #                 the @id option is not given there.
+# @base-directory #optional May be specified for any node. Normally, whenever a
+#                 filename is specified which is supposed to be relative to 
this
+#                 node (such as relative backing filenames), the base directory
+#                 to be used is the directory the image file of this node is 
in,
+#                 which is simply prepended to the relative filename. Using 
this
+#                 option, the string which is prepended (i.e. the base
+#                 directory) can be overridden.
+#                 (Since 2.7)
 # @discard:       #optional discard-related options (default: ignore)
 # @cache:         #optional cache-related options
 # @aio:           #optional AIO backend (default: threads)
@@ -2073,6 +2081,7 @@
   'base': { 'driver': 'BlockdevDriver',
             '*id': 'str',
             '*node-name': 'str',
+            '*base-directory': 'str',
             '*discard': 'BlockdevDiscardOptions',
             '*cache': 'BlockdevCacheOptions',
             '*aio': 'BlockdevAioOptions',
-- 
2.8.0