block: Allow reference for bdrv_file_open()

Allow specifying a reference to an existing block device (by name) for
bdrv_file_open() instead of a filename and/or options.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -858,9 +858,10 @@ free_and_fail:
  * dictionary, it needs to use QINCREF() before calling bdrv_file_open.
  */
 int bdrv_file_open(BlockDriverState **pbs, const char *filename,
-                   QDict *options, int flags, Error **errp)
+                   const char *reference, QDict *options, int flags,
+                   Error **errp)
 {
-    BlockDriverState *bs;
+    BlockDriverState *bs = NULL;
     BlockDriver *drv;
     const char *drvname;
     bool allow_protocol_prefix = false;
@@ -872,6 +873,24 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
         options = qdict_new();
     }
 
+    if (reference) {
+        if (filename || qdict_size(options)) {
+            error_setg(errp, "Cannot reference an existing block device with "
+                       "additional options or a new filename");
+            return -EINVAL;
+        }
+        QDECREF(options);
+
+        bs = bdrv_find(reference);
+        if (!bs) {
+            error_setg(errp, "Cannot find block device '%s'", reference);
+            return -ENODEV;
+        }
+        bdrv_ref(bs);
+        *pbs = bs;
+        return 0;
+    }
+
     bs = bdrv_new("");
     bs->options = options;
     options = qdict_clone_shallow(options);
@@ -1124,7 +1143,7 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
 
     qdict_extract_subqdict(options, &file_options, "file.");
 
-    ret = bdrv_file_open(&file, filename, file_options,
+    ret = bdrv_file_open(&file, filename, NULL, file_options,
                          bdrv_open_flags(bs, flags | BDRV_O_UNMAP), &local_err);
     if (ret < 0) {
         goto fail;

block/blkdebug.c

@@ -403,7 +403,7 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    ret = bdrv_file_open(&bs->file, filename, NULL, flags, &local_err);
+    ret = bdrv_file_open(&bs->file, filename, NULL, NULL, flags, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         goto fail;

block/blkverify.c

@@ -141,7 +141,7 @@ static int blkverify_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    ret = bdrv_file_open(&bs->file, raw, NULL, flags, &local_err);
+    ret = bdrv_file_open(&bs->file, raw, NULL, NULL, flags, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         goto fail;

block/cow.c

@@ -351,7 +351,8 @@ static int cow_create(const char *filename, QEMUOptionParameter *options,
         return ret;
     }
 
-    ret = bdrv_file_open(&cow_bs, filename, NULL, BDRV_O_RDWR, &local_err);
+    ret = bdrv_file_open(&cow_bs, filename, NULL, NULL, BDRV_O_RDWR,
+                         &local_err);
     if (ret < 0) {
         qerror_report_err(local_err);
         error_free(local_err);

block/qcow.c

@@ -691,7 +691,8 @@ static int qcow_create(const char *filename, QEMUOptionParameter *options,
         return ret;
     }
 
-    ret = bdrv_file_open(&qcow_bs, filename, NULL, BDRV_O_RDWR, &local_err);
+    ret = bdrv_file_open(&qcow_bs, filename, NULL, NULL, BDRV_O_RDWR,
+                         &local_err);
     if (ret < 0) {
         qerror_report_err(local_err);
         error_free(local_err);

block/qcow2.c

@@ -1483,7 +1483,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
         return ret;
     }
 
-    ret = bdrv_file_open(&bs, filename, NULL, BDRV_O_RDWR, &local_err);
+    ret = bdrv_file_open(&bs, filename, NULL, NULL, BDRV_O_RDWR, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         return ret;

block/qed.c

@@ -563,8 +563,8 @@ static int qed_create(const char *filename, uint32_t cluster_size,
         return ret;
     }
 
-    ret = bdrv_file_open(&bs, filename, NULL, BDRV_O_RDWR | BDRV_O_CACHE_WB,
-                         &local_err);
+    ret = bdrv_file_open(&bs, filename, NULL, NULL,
+                         BDRV_O_RDWR | BDRV_O_CACHE_WB, &local_err);
     if (ret < 0) {
         qerror_report_err(local_err);
         error_free(local_err);

block/sheepdog.c

@@ -1534,7 +1534,7 @@ static int sd_prealloc(const char *filename)
     Error *local_err = NULL;
     int ret;
 
-    ret = bdrv_file_open(&bs, filename, NULL, BDRV_O_RDWR, &local_err);
+    ret = bdrv_file_open(&bs, filename, NULL, NULL, BDRV_O_RDWR, &local_err);
     if (ret < 0) {
         qerror_report_err(local_err);
         error_free(local_err);
@@ -1695,7 +1695,7 @@ static int sd_create(const char *filename, QEMUOptionParameter *options,
             goto out;
         }
 
-        ret = bdrv_file_open(&bs, backing_file, NULL, 0, &local_err);
+        ret = bdrv_file_open(&bs, backing_file, NULL, NULL, 0, &local_err);
         if (ret < 0) {
             qerror_report_err(local_err);
             error_free(local_err);

block/vhdx.c

@@ -1797,7 +1797,7 @@ static int vhdx_create(const char *filename, QEMUOptionParameter *options,
         goto exit;
     }
 
-    ret = bdrv_file_open(&bs, filename, NULL, BDRV_O_RDWR, &local_err);
+    ret = bdrv_file_open(&bs, filename, NULL, NULL, BDRV_O_RDWR, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         goto exit;

block/vmdk.c

@@ -769,8 +769,8 @@ static int vmdk_parse_extents(const char *desc, BlockDriverState *bs,
 
         path_combine(extent_path, sizeof(extent_path),
                 desc_file_path, fname);
-        ret = bdrv_file_open(&extent_file, extent_path, NULL, bs->open_flags,
-                             errp);
+        ret = bdrv_file_open(&extent_file, extent_path, NULL, NULL,
+                             bs->open_flags, errp);
         if (ret) {
             return ret;
         }
@@ -1469,7 +1469,7 @@ static int vmdk_create_extent(const char *filename, int64_t filesize,
         goto exit;
     }
 
-    ret = bdrv_file_open(&bs, filename, NULL, BDRV_O_RDWR, &local_err);
+    ret = bdrv_file_open(&bs, filename, NULL, NULL, BDRV_O_RDWR, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         goto exit;
@@ -1807,7 +1807,7 @@ static int vmdk_create(const char *filename, QEMUOptionParameter *options,
             goto exit;
         }
     }
-    ret = bdrv_file_open(&new_bs, filename, NULL, BDRV_O_RDWR, &local_err);
+    ret = bdrv_file_open(&new_bs, filename, NULL, NULL, BDRV_O_RDWR, &local_err);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not write description");
         goto exit;

include/block/block.h

@@ -184,7 +184,8 @@ void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top);
 int bdrv_parse_cache_flags(const char *mode, int *flags);
 int bdrv_parse_discard_flags(const char *mode, int *flags);
 int bdrv_file_open(BlockDriverState **pbs, const char *filename,
-                   QDict *options, int flags, Error **errp);
+                   const char *reference, QDict *options, int flags,
+                   Error **errp);
 int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp);
 int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
               int flags, BlockDriver *drv, Error **errp);

qemu-io.c

@@ -59,7 +59,7 @@ static int openfile(char *name, int flags, int growable, QDict *opts)
     }
 
     if (growable) {
-        if (bdrv_file_open(&qemuio_bs, name, opts, flags, &local_err)) {
+        if (bdrv_file_open(&qemuio_bs, name, NULL, opts, flags, &local_err)) {
             fprintf(stderr, "%s: can't open device %s: %s\n", progname, name,
                     error_get_pretty(local_err));
             error_free(local_err);