[PATCH] init: Add bdev fs printk if mount_block_root failed

[Angus Chen <angus.chen@jaguarmicro.com>]

Attempt to printk all bdev fstype as root gives the following kernel panic:

[    1.729006] VFS: Cannot open root device "vda" or unknown-block(253,0): error -19
[    1.730603] Please append a correct "root=" boot option; here are the available partitions:
[    1.732323] fd00          256000 vda
[    1.732329]  driver: virtio_blk
[    1.734194] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(253,0)
[    1.734771] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.4.0-rc2+ #53
[    1.735194] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1ubuntu1 04/01/2014
[    1.735772] Call Trace:
[    1.735950]  <TASK>
[    1.736113]  dump_stack_lvl+0x32/0x50
[    1.736367]  panic+0x108/0x310
[    1.736570]  mount_block_root+0x161/0x310
[    1.736849]  ? rdinit_setup+0x40/0x40
[    1.737088]  prepare_namespace+0x10c/0x180
[    1.737393]  kernel_init_freeable+0x354/0x450
[    1.737707]  ? rest_init+0xd0/0xd0
[    1.737945]  kernel_init+0x16/0x130
[    1.738196]  ret_from_fork+0x1f/0x30

QEMU command line:
"qemu-system-x86_64 -append root=/dev/vda rootfstype=ext4 ..."

This error is because ext4 is not buildin and request ext4 module fail.

As a hint, printk all the bdev fstype available for prompts.

Signed-off-by: Angus Chen <angus.chen@jaguarmicro.com>
---
 init/do_mounts.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 811e94daf0a8..7fa48590c681 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -427,8 +427,19 @@ void __init mount_block_root(char *name, int flags)
 		printk("VFS: Cannot open root device \"%s\" or %s: error %d\n",
 				root_device_name, b, err);
 		printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");
-
 		printk_all_partitions();
+
+		if (root_fs_names)
+			num_fs = list_bdev_fs_names(fs_names, PAGE_SIZE);
+		if (!num_fs)
+			pr_err("Can't find any bdev filesystem to be used for mount!\n");
+		else {
+			pr_err("List of all bdev filesystem:\n");
+			for (i = 0, p = fs_names; i < num_fs; i++, p += strlen(p)+1)
+				pr_err(" %s", p);
+			pr_err("\n");
+		}
+
 		panic("VFS: Unable to mount root fs on %s", b);
 	}
 	if (!(flags & SB_RDONLY)) {
-- 
2.25.1