block: Make essential BlockDriver objects public

There are some block drivers which are essential to QEMU and may not be
removed: These are raw, file and qcow2 (as the default non-raw format).
Make their BlockDriver objects public so they can be directly referenced
throughout the block layer without needing to call bdrv_find_format()
and having to deal with an error at runtime, while the real problem
occurred during linking (where raw, file or qcow2 were not linked into
qemu).

Cc: qemu-stable@nongnu.org
Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 5f535a9)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

block/qcow2.c

@@ -2404,7 +2404,7 @@ static QemuOptsList qcow2_create_opts = {
     }
 };
 
-static BlockDriver bdrv_qcow2 = {
+BlockDriver bdrv_qcow2 = {
     .format_name        = "qcow2",
     .instance_size      = sizeof(BDRVQcowState),
     .bdrv_probe         = qcow2_probe,

block/raw-posix.c

@@ -1585,7 +1585,7 @@ static QemuOptsList raw_create_opts = {
     }
 };
 
-static BlockDriver bdrv_file = {
+BlockDriver bdrv_file = {
     .format_name = "file",
     .protocol_name = "file",
     .instance_size = sizeof(BDRVRawState),

block/raw-win32.c

@@ -540,7 +540,7 @@ static QemuOptsList raw_create_opts = {
     }
 };
 
-static BlockDriver bdrv_file = {
+BlockDriver bdrv_file = {
     .format_name	= "file",
     .protocol_name	= "file",
     .instance_size	= sizeof(BDRVRawState),

block/raw_bsd.c

@@ -173,7 +173,7 @@ static int raw_probe(const uint8_t *buf, int buf_size, const char *filename)
     return 1;
 }
 
-static BlockDriver bdrv_raw = {
+BlockDriver bdrv_raw = {
     .format_name          = "raw",
     .bdrv_probe           = &raw_probe,
     .bdrv_reopen_prepare  = &raw_reopen_prepare,

include/block/block_int.h

@@ -395,6 +395,14 @@ struct BlockDriverState {
     Error *backing_blocker;
 };
 
+
+/* Essential block drivers which must always be statically linked into qemu, and
+ * which therefore can be accessed without using bdrv_find_format() */
+extern BlockDriver bdrv_file;
+extern BlockDriver bdrv_raw;
+extern BlockDriver bdrv_qcow2;
+
+
 int get_tmp_filename(char *filename, int size);
 
 void bdrv_set_io_limits(BlockDriverState *bs,