init: DEBUG_BLOCK_EXT_DEVT requires explicit root= param

DEBUG_BLOCK_EXT_DEVT shuffles SCSI and IDE device numbers and root
device number set using rdev become meaningless.  Root devices should
be explicitly specified using textual names.  Warn about it if root
can't be found and DEBUG_BLOCK_EXT_DEVT is enabled.  Also, add warning
to the help text.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 3715feb8446d..d055b1914c3d 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -263,6 +263,10 @@ retry:
                 printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");
 
                 printk_all_partitions();
+#ifdef CONFIG_DEBUG_BLOCK_EXT_DEVT
+                printk("DEBUG_BLOCK_EXT_DEVT is enabled, you need to specify "
+                       "explicit textual name for \"root=\" boot option.\n");
+#endif
                 panic("VFS: Unable to mount root fs on %s", b);
         }