This is the common but non-trivial steps to assign or change the
backing_hd of BDS.
Signed-off-by: Fam Zheng <f...@redhat.com>
---
block.c | 46 ++++++++++++++++++++++++++++++++++++++--------
include/block/block.h | 1 +
2 files changed, 39 insertions(+), 8 deletions(-)
diff --git a/block.c b/block.c
index 684b9d6..9caade9 100644
--- a/block.c
+++ b/block.c
@@ -1041,6 +1041,32 @@ fail:
return ret;
}
+void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
+{
+ if (backing_hd) {
+ /* Grab the reference before unref original backing_hd, so we are safe
+ * when rebasing in the backing chain.
+ */
+ bdrv_ref(backing_hd);
+ }
+
+ if (bs->backing_hd) {
+ bdrv_unref(bs->backing_hd);
+ }
+
+ bs->backing_hd = backing_hd;
+ if (!backing_hd) {
+ bs->backing_file[0] = '\0';
+ bs->backing_format[0] = '\0';
+ goto out;
+ }
+ pstrcpy(bs->backing_file, sizeof(bs->backing_file), backing_hd->filename);
+ pstrcpy(bs->backing_format, sizeof(bs->backing_format),
+ backing_hd->drv ? backing_hd->drv->format_name : "");
+out:
+ bdrv_refresh_limits(bs);
+}
+
/*
* Opens the backing file for a BlockDriverState if not yet open
*
@@ -1054,6 +1080,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict
*options, Error **errp)
char backing_filename[PATH_MAX];
int back_flags, ret;
BlockDriver *back_drv = NULL;
+ BlockDriverState *backing_hd;
Error *local_err = NULL;
if (bs->backing_hd != NULL) {
@@ -1077,6 +1104,8 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict
*options, Error **errp)
sizeof(backing_filename));
}
+ backing_hd = bdrv_new("");
+
if (bs->backing_format[0] != '\0') {
back_drv = bdrv_find_format(bs->backing_format);
}
@@ -1085,23 +1114,24 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict
*options, Error **errp)
back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT |
BDRV_O_COPY_ON_READ);
- assert(bs->backing_hd == NULL);
- ret = bdrv_open(&bs->backing_hd,
+ ret = bdrv_open(&backing_hd,
*backing_filename ? backing_filename : NULL, NULL, options,
back_flags, back_drv, &local_err);
if (ret < 0) {
bs->backing_hd = NULL;
+ bdrv_unref(backing_hd);
+ backing_hd = NULL;
bs->open_flags |= BDRV_O_NO_BACKING;
error_setg(errp, "Could not open backing file: %s",
error_get_pretty(local_err));
error_free(local_err);
return ret;
}
-
- if (bs->backing_hd->file) {
- pstrcpy(bs->backing_file, sizeof(bs->backing_file),
- bs->backing_hd->file->filename);
- }
+ bdrv_set_backing_hd(bs, backing_hd);
+ /* Now we have refcnt = 2 on backing_hd by bdrv_new and
+ * bdrv_set_backing_hd, while we only need 1 */
+ assert(backing_hd->refcnt == 2);
+ bdrv_unref(backing_hd);
/* Recalculate the BlockLimits with the backing file */
bdrv_refresh_limits(bs);
@@ -1923,7 +1953,7 @@ void bdrv_append(BlockDriverState *bs_new,
BlockDriverState *bs_top)
/* The contents of 'tmp' will become bs_top, as we are
* swapping bs_new and bs_top contents. */
- bs_top->backing_hd = bs_new;
+ bdrv_set_backing_hd(bs_top, bs_new);
bs_top->open_flags &= ~BDRV_O_NO_BACKING;
pstrcpy(bs_top->backing_file, sizeof(bs_top->backing_file),
bs_new->filename);
diff --git a/include/block/block.h b/include/block/block.h
index a46f70a..ee1582d 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -208,6 +208,7 @@ int bdrv_parse_discard_flags(const char *mode, int *flags);
int bdrv_open_image(BlockDriverState **pbs, const char *filename,
QDict *options, const char *bdref_key, int flags,
bool allow_none, Error **errp);
+void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd);
int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp);
int bdrv_open(BlockDriverState **pbs, const char *filename,
const char *reference, QDict *options, int flags,
--
1.8.5.4
