@@ -1247,6 +1247,20 @@ out:
bdrv_refresh_limits(bs, NULL);
}
+#define ALLOW_WRITE_BACKING_FILE "allow-write-backing-file"
+static QemuOptsList backing_file_opts = {
+ .name = "backing_file",
+ .head = QTAILQ_HEAD_INITIALIZER(backing_file_opts.head),
+ .desc = {
+ {
+ .name = ALLOW_WRITE_BACKING_FILE,
+ .type = QEMU_OPT_BOOL,
+ .help = "allow write to backing file",
+ },
+ { /* end of list */ }
+ },
+};
+
/*
* Opens the backing file for a BlockDriverState if not yet open
*
@@ -1261,6 +1275,8 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
int ret = 0;
BlockDriverState *backing_hd;
Error *local_err = NULL;
+ QemuOpts *opts = NULL;
+ int flags;
if (bs->backing_hd != NULL) {
QDECREF(options);
@@ -1273,6 +1289,19 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
}
bs->open_flags &= ~BDRV_O_NO_BACKING;
+ flags = bdrv_backing_flags(bs->open_flags);
+
+ opts = qemu_opts_create(&backing_file_opts, NULL, 0, &error_abort);
+ qemu_opts_absorb_qdict(opts, options, &local_err);
+ if (local_err) {
+ ret = -EINVAL;
+ goto free_exit;
+ }
+ if (qemu_opt_get_bool(opts, ALLOW_WRITE_BACKING_FILE, false)) {
+ flags |= BDRV_O_RDWR;
+ }
+ qemu_opts_del(opts);
+
if (qdict_haskey(options, "file.filename")) {
backing_filename[0] = '\0';
} else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) {
@@ -1305,7 +1334,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
assert(bs->backing_hd == NULL);
ret = bdrv_open(&backing_hd,
*backing_filename ? backing_filename : NULL, NULL, options,
- bdrv_backing_flags(bs->open_flags), NULL, &local_err);
+ flags, NULL, &local_err);
if (ret < 0) {
bdrv_unref(backing_hd);
backing_hd = NULL;