block: Add reference parameter to bdrv_open()

Allow bdrv_open() to handle references to existing block devices just as
bdrv_file_open() is already capable of.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -1046,7 +1046,7 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
     }
 
     if (!drv->bdrv_file_open) {
-        ret = bdrv_open(&bs, filename, options, flags, drv, &local_err);
+        ret = bdrv_open(&bs, filename, NULL, options, flags, drv, &local_err);
         options = NULL;
     } else {
         ret = bdrv_open_common(bs, NULL, options, flags, drv, &local_err);
@@ -1125,7 +1125,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
 
     assert(bs->backing_hd == NULL);
     ret = bdrv_open(&bs->backing_hd,
-                    *backing_filename ? backing_filename : NULL, options,
+                    *backing_filename ? backing_filename : NULL, NULL, options,
                     back_flags, back_drv, &local_err);
     if (ret < 0) {
         bs->backing_hd = NULL;
@@ -1206,7 +1206,7 @@ int bdrv_open_image(BlockDriverState **pbs, const char *filename,
             goto done;
         }
 
-        ret = bdrv_open(pbs, filename, image_options, flags, NULL, errp);
+        ret = bdrv_open(pbs, filename, NULL, image_options, flags, NULL, errp);
     } else {
         ret = bdrv_file_open(pbs, filename, reference, image_options, flags,
                              errp);
@@ -1227,9 +1227,14 @@ done:
  *
  * If *pbs is NULL, a new BDS will be created with a pointer to it stored there.
  * If it is not NULL, the referenced BDS will be reused.
+ *
+ * The reference parameter may be used to specify an existing block device which
+ * should be opened. If specified, neither options nor a filename may be given,
+ * nor can an existing BDS be reused (that is, *pbs has to be NULL).
  */
-int bdrv_open(BlockDriverState **pbs, const char *filename, QDict *options,
-              int flags, BlockDriver *drv, Error **errp)
+int bdrv_open(BlockDriverState **pbs, const char *filename,
+              const char *reference, QDict *options, int flags,
+              BlockDriver *drv, Error **errp)
 {
     int ret;
     /* TODO: extra byte is a hack to ensure MAX_PATH space on Windows. */
@@ -1240,6 +1245,31 @@ int bdrv_open(BlockDriverState **pbs, const char *filename, QDict *options,
 
     assert(pbs);
 
+    if (reference) {
+        bool options_non_empty = options ? qdict_size(options) : false;
+        QDECREF(options);
+
+        if (*pbs) {
+            error_setg(errp, "Cannot reuse an existing BDS when referencing "
+                       "another block device");
+            return -EINVAL;
+        }
+
+        if (filename || options_non_empty) {
+            error_setg(errp, "Cannot reference an existing block device with "
+                       "additional options or a new filename");
+            return -EINVAL;
+        }
+
+        bs = bdrv_lookup_bs(reference, reference, errp);
+        if (!bs) {
+            return -ENODEV;
+        }
+        bdrv_ref(bs);
+        *pbs = bs;
+        return 0;
+    }
+
     if (*pbs) {
         bs = *pbs;
     } else {
@@ -1268,7 +1298,7 @@ int bdrv_open(BlockDriverState **pbs, const char *filename, QDict *options,
         /* Get the required size from the image */
         QINCREF(options);
         bs1 = NULL;
-        ret = bdrv_open(&bs1, filename, options, BDRV_O_NO_BACKING,
+        ret = bdrv_open(&bs1, filename, NULL, options, BDRV_O_NO_BACKING,
                         drv, &local_err);
         if (ret < 0) {
             goto fail;
@@ -5309,7 +5339,7 @@ void bdrv_img_create(const char *filename, const char *fmt,
                 flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
 
             bs = NULL;
-            ret = bdrv_open(&bs, backing_file->value.s, NULL, back_flags,
+            ret = bdrv_open(&bs, backing_file->value.s, NULL, NULL, back_flags,
                             backing_drv, &local_err);
             if (ret < 0) {
                 error_setg_errno(errp, -ret, "Could not open '%s': %s",

block/qcow2.c

@@ -1553,7 +1553,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
      */
     BlockDriver* drv = bdrv_find_format("qcow2");
     assert(drv != NULL);
-    ret = bdrv_open(&bs, filename, NULL,
+    ret = bdrv_open(&bs, filename, NULL, NULL,
         BDRV_O_RDWR | BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH, drv, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
@@ -1604,7 +1604,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
     bs = NULL;
 
     /* Reopen the image without BDRV_O_NO_FLUSH to flush it before returning */
-    ret = bdrv_open(&bs, filename, NULL,
+    ret = bdrv_open(&bs, filename, NULL, NULL,
                     BDRV_O_RDWR | BDRV_O_CACHE_WB | BDRV_O_NO_BACKING,
                     drv, &local_err);
     if (local_err) {

block/vmdk.c

@@ -1756,7 +1756,8 @@ static int vmdk_create(const char *filename, QEMUOptionParameter *options,
     }
     if (backing_file) {
         BlockDriverState *bs = NULL;
-        ret = bdrv_open(&bs, backing_file, NULL, BDRV_O_NO_BACKING, NULL, errp);
+        ret = bdrv_open(&bs, backing_file, NULL, NULL, BDRV_O_NO_BACKING, NULL,
+                        errp);
         if (ret != 0) {
             goto exit;
         }

block/vvfat.c

@@ -2937,7 +2937,7 @@ static int enable_write_target(BDRVVVFATState *s)
     }
 
     s->qcow = NULL;
-    ret = bdrv_open(&s->qcow, s->qcow_filename, NULL,
+    ret = bdrv_open(&s->qcow, s->qcow_filename, NULL, NULL,
             BDRV_O_RDWR | BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH, bdrv_qcow,
             &local_err);
     if (ret < 0) {

blockdev.c

@@ -504,7 +504,7 @@ static DriveInfo *blockdev_init(const char *file, QDict *bs_opts,
     bdrv_flags |= ro ? 0 : BDRV_O_RDWR;
 
     QINCREF(bs_opts);
-    ret = bdrv_open(&dinfo->bdrv, file, bs_opts, bdrv_flags, drv, &error);
+    ret = bdrv_open(&dinfo->bdrv, file, NULL, bs_opts, bdrv_flags, drv, &error);
 
     if (ret < 0) {
         error_setg(errp, "could not open disk image %s: %s",
@@ -1333,7 +1333,7 @@ static void external_snapshot_prepare(BlkTransactionState *common,
     /* TODO Inherit bs->options or only take explicit options with an
      * extended QMP command? */
     assert(state->new_bs == NULL);
-    ret = bdrv_open(&state->new_bs, new_image_file, options,
+    ret = bdrv_open(&state->new_bs, new_image_file, NULL, options,
                     flags | BDRV_O_NO_BACKING, drv, &local_err);
     /* We will manually add the backing_hd field to the bs later */
     if (ret != 0) {
@@ -1582,7 +1582,7 @@ static void qmp_bdrv_open_encrypted(BlockDriverState *bs, const char *filename,
     Error *local_err = NULL;
     int ret;
 
-    ret = bdrv_open(&bs, filename, NULL, bdrv_flags, drv, &local_err);
+    ret = bdrv_open(&bs, filename, NULL, NULL, bdrv_flags, drv, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         return;
@@ -2019,7 +2019,7 @@ void qmp_drive_backup(const char *device, const char *target,
     }
 
     target_bs = NULL;
-    ret = bdrv_open(&target_bs, target, NULL, flags, drv, &local_err);
+    ret = bdrv_open(&target_bs, target, NULL, NULL, flags, drv, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         return;
@@ -2162,8 +2162,8 @@ void qmp_drive_mirror(const char *device, const char *target,
      * file.
      */
     target_bs = NULL;
-    ret = bdrv_open(&target_bs, target, NULL, flags | BDRV_O_NO_BACKING, drv,
-                    &local_err);
+    ret = bdrv_open(&target_bs, target, NULL, NULL, flags | BDRV_O_NO_BACKING,
+                    drv, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         return;

hw/block/xen_disk.c

@@ -813,8 +813,8 @@ static int blk_connect(struct XenDevice *xendev)
             Error *local_err = NULL;
             BlockDriver *drv = bdrv_find_whitelisted_format(blkdev->fileproto,
                                                            readonly);
-            if (bdrv_open(&blkdev->bs,
-                          blkdev->filename, NULL, qflags, drv, &local_err) != 0)
+            if (bdrv_open(&blkdev->bs, blkdev->filename, NULL, NULL, qflags,
+                          drv, &local_err) != 0)
             {
                 xen_be_printf(&blkdev->xendev, 0, "error: %s\n",
                               error_get_pretty(local_err));

include/block/block.h

@@ -190,8 +190,9 @@ int bdrv_open_image(BlockDriverState **pbs, const char *filename,
                     QDict *options, const char *bdref_key, int flags,
                     bool force_raw, bool allow_none, Error **errp);
 int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp);
-int bdrv_open(BlockDriverState **pbs, const char *filename, QDict *options,
-              int flags, BlockDriver *drv, Error **errp);
+int bdrv_open(BlockDriverState **pbs, const char *filename,
+              const char *reference, QDict *options, int flags,
+              BlockDriver *drv, Error **errp);
 BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,
                                     BlockDriverState *bs, int flags);
 int bdrv_reopen_multiple(BlockReopenQueue *bs_queue, Error **errp);

qemu-img.c

@@ -289,7 +289,7 @@ static BlockDriverState *bdrv_new_open(const char *filename,
         drv = NULL;
     }
 
-    ret = bdrv_open(&bs, filename, NULL, flags, drv, &local_err);
+    ret = bdrv_open(&bs, filename, NULL, NULL, flags, drv, &local_err);
     if (ret < 0) {
         error_report("Could not open '%s': %s", filename,
                      error_get_pretty(local_err));
@@ -2312,7 +2312,7 @@ static int img_rebase(int argc, char **argv)
 
         bs_old_backing = bdrv_new("old_backing");
         bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
-        ret = bdrv_open(&bs_old_backing, backing_name, NULL, BDRV_O_FLAGS,
+        ret = bdrv_open(&bs_old_backing, backing_name, NULL, NULL, BDRV_O_FLAGS,
                         old_backing_drv, &local_err);
         if (ret) {
             error_report("Could not open old backing file '%s': %s",
@@ -2322,8 +2322,8 @@ static int img_rebase(int argc, char **argv)
         }
         if (out_baseimg[0]) {
             bs_new_backing = bdrv_new("new_backing");
-            ret = bdrv_open(&bs_new_backing, out_baseimg, NULL, BDRV_O_FLAGS,
-                        new_backing_drv, &local_err);
+            ret = bdrv_open(&bs_new_backing, out_baseimg, NULL, NULL,
+                            BDRV_O_FLAGS, new_backing_drv, &local_err);
             if (ret) {
                 error_report("Could not open new backing file '%s': %s",
                              out_baseimg, error_get_pretty(local_err));

qemu-io.c

@@ -68,7 +68,9 @@ static int openfile(char *name, int flags, int growable, QDict *opts)
     } else {
         qemuio_bs = bdrv_new("hda");
 
-        if (bdrv_open(&qemuio_bs, name, opts, flags, NULL, &local_err) < 0) {
+        if (bdrv_open(&qemuio_bs, name, NULL, opts, flags, NULL, &local_err)
+            < 0)
+        {
             fprintf(stderr, "%s: can't open device %s: %s\n", progname, name,
                     error_get_pretty(local_err));
             error_free(local_err);

qemu-nbd.c

@@ -597,7 +597,7 @@ int main(int argc, char **argv)
 
     bs = bdrv_new("hda");
     srcpath = argv[optind];
-    ret = bdrv_open(&bs, srcpath, NULL, flags, drv, &local_err);
+    ret = bdrv_open(&bs, srcpath, NULL, NULL, flags, drv, &local_err);
     if (ret < 0) {
         errno = -ret;
         err(EXIT_FAILURE, "Failed to bdrv_open '%s': %s", argv[optind],