[Qemu-block] [PATCH v3 3/5] block: Add bdrv_filename()

[Max Reitz]

Split the part which actually refreshes the BlockDriverState.filename
field off of bdrv_refresh_filename() into a more generic function
bdrv_filename(), which first calls bdrv_refresh_filename() and then
stores a qemu-usable filename into the given buffer instead of
BlockDriverState.filename.

Since bdrv_refresh_filename() therefore no longer refreshes that field,
some calls to that function have to be replaced by calls to
bdrv_filename() "manually" refreshing the BDS filename field (this is
only temporary).

Additionally, a wrapper function bdrv_filename_alloc() is added which
allocates a buffer of size PATH_MAX, call bdrv_filename() on that buffer
and returns it, since needing a temporary buffer for the filename is a
rather common pattern.

Signed-off-by: Max Reitz <address@hidden>
---
 block.c               | 39 ++++++++++++++++++++++++++++++++-------
 block/blkverify.c     |  3 ++-
 block/quorum.c        |  2 +-
 include/block/block.h |  2 ++
 4 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/block.c b/block.c
index 1572785..d2a3e8d 100644
--- a/block.c
+++ b/block.c
@@ -1559,7 +1559,7 @@ static int bdrv_open_inherit(BlockDriverState **pbs, 
const char *filename,
         }
     }
 
-    bdrv_refresh_filename(bs);
+    bdrv_filename(bs, bs->filename, sizeof(bs->filename));
 
     /* For snapshot=on, create a temporary qcow2 overlay. bs points to the
      * temporary snapshot afterwards. */
@@ -4153,9 +4153,6 @@ static bool append_open_options(QDict *d, 
BlockDriverState *bs)
  *  - full_open_options: Options which, when given when opening a block device
  *                       (without a filename), result in a BDS (mostly)
  *                       equalling the given one
- *  - filename: If exact_filename is set, it is copied here. Otherwise,
- *              full_open_options is converted to a JSON object, prefixed with
- *              "json:" (for use through the JSON pseudo protocol) and put 
here.
  */
 void bdrv_refresh_filename(BlockDriverState *bs)
 {
@@ -4242,15 +4239,43 @@ void bdrv_refresh_filename(BlockDriverState *bs)
 
         bs->full_open_options = opts;
     }
+}
+
+/* First refreshes exact_filename and full_open_options by calling
+ * bdrv_refresh_filename(). Then, if exact_filename is set, it is copied into
+ * the target buffer. Otherwise, full_open_options is converted to a JSON
+ * object, prefixed with "json:" (for use through the JSON pseudo protocol) and
+ * put there.
+ *
+ * If sz > 0, the string put into the buffer will always be null-terminated.
+ *
+ * Returns @dest.
+ */
+char *bdrv_filename(BlockDriverState *bs, char *dest, size_t sz)
+{
+    bdrv_refresh_filename(bs);
+
+    if (sz > INT_MAX) {
+        sz = INT_MAX;
+    }
 
     if (bs->exact_filename[0]) {
-        pstrcpy(bs->filename, sizeof(bs->filename), bs->exact_filename);
+        pstrcpy(dest, sz, bs->exact_filename);
     } else if (bs->full_open_options) {
         QString *json = qobject_to_json(QOBJECT(bs->full_open_options));
-        snprintf(bs->filename, sizeof(bs->filename), "json:%s",
-                 qstring_get_str(json));
+        snprintf(dest, sz, "json:%s", qstring_get_str(json));
         QDECREF(json);
     }
+
+    return dest;
+}
+
+/* Wrapper around bdrv_filename() using g_malloc(PATH_MAX) for the destination
+ * buffer.
+ */
+char *bdrv_filename_alloc(BlockDriverState *bs)
+{
+    return bdrv_filename(bs, g_malloc(PATH_MAX), PATH_MAX);
 }
 
 /* This accessor function purpose is to allow the device models to access the
diff --git a/block/blkverify.c b/block/blkverify.c
index d277e63..cb9ce02 100644
--- a/block/blkverify.c
+++ b/block/blkverify.c
@@ -309,7 +309,8 @@ static void blkverify_refresh_filename(BlockDriverState *bs)
     BDRVBlkverifyState *s = bs->opaque;
 
     /* bs->file has already been refreshed */
-    bdrv_refresh_filename(s->test_file);
+    bdrv_filename(s->test_file, s->test_file->filename,
+                  sizeof(s->test_file->filename));
 
     if (bs->file->full_open_options && s->test_file->full_open_options) {
         QDict *opts = qdict_new();
diff --git a/block/quorum.c b/block/quorum.c
index 2f6c45f..00d1fb0 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -1003,7 +1003,7 @@ static void quorum_refresh_filename(BlockDriverState *bs)
     int i;
 
     for (i = 0; i < s->num_children; i++) {
-        bdrv_refresh_filename(s->bs[i]);
+        bdrv_filename(s->bs[i], s->bs[i]->filename, 
sizeof(s->bs[i]->filename));
         if (!s->bs[i]->full_open_options) {
             return;
         }
diff --git a/include/block/block.h b/include/block/block.h
index a78e4f1..4be6c18 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -267,6 +267,8 @@ 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);
+char *bdrv_filename(BlockDriverState *bs, char *dest, size_t sz);
+char *bdrv_filename_alloc(BlockDriverState *bs);
 int bdrv_truncate(BlockDriverState *bs, int64_t offset);
 int64_t bdrv_nb_sectors(BlockDriverState *bs);
 int64_t bdrv_getlength(BlockDriverState *bs);
-- 
2.4.6