[PATCH 1/3] init: print some info about UUID and LABEL in name_to_dev_t()

[Tiezhu Yang <yangtiezhu@loongson.cn>]

If there is no valid initrd, but root=UUID or root=LABEL is used
in the command line, boot hangs like this:

[    5.739815] VFS: Cannot open root device "UUID=19957230-2e15-494c-8dfa-84aab3591961" or unknown-block(0,0): error -6
[    5.750280] Please append a correct "root=" boot option; here are the available partitions:
[    5.856059] 0800       125034840 sda
[    5.856061]  driver: sd
[    5.862124]   0801          307200 sda1 d5077411-3d87-4f85-b312-8cc309ef9073
[    5.862128]
[    5.870603]   0802         1048576 sda2 aae0dd30-e5f5-44e1-994e-d47bf5ce2e52
[    5.870606]
[    5.879080]   0803        52428800 sda3 759079ee-85fa-4636-9de7-1ac0643ab87e
[    5.879083]
[    5.887558]   0804         8388608 sda4 439c4b0a-7b4f-4434-82f1-f9d380b55fb9
[    5.887560]
[    5.896035]   0805        62860288 sda5 ee52e951-1315-4fab-a3e5-45c6eeae6ce6
[    5.910575] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[    5.918796] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) ]---

The above log is very useful, but some users still need time
to analysis the cause [1, 2]. It is better to print some info
to explicitly tell the users root=UUID or root=LABEL is not
supported without initrd.

[1] https://unix.stackexchange.com/questions/93767/why-cant-i-specify-my-root-fs-with-a-uuid
[2] https://unix.stackexchange.com/questions/302795/how-to-identify-root-partition-via-uuid-without-initramfs-initrd

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 init/do_mounts.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 7058e14..2c1c492 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -290,6 +290,14 @@ dev_t name_to_dev_t(const char *name)
 	if (strncmp(name, "/dev/", 5) == 0)
 		return devt_from_devname(name + 5);
 #endif
+	if (strncmp(name, "UUID=", 5) == 0) {
+		pr_info("root=UUID is not supported without initrd\n");
+		return 0;
+	}
+	if (strncmp(name, "LABEL=", 6) == 0) {
+		pr_info("root=LABEL is not supported without initrd\n");
+		return 0;
+	}
 	return devt_from_devnum(name);
 }
 EXPORT_SYMBOL_GPL(name_to_dev_t);
-- 
2.1.0