USB stick as root device does not work

DISCUSSION Micha Nelissen 3 participants 4 messages May 22, 2011 – May 23, 2011

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Micha Nelissen

author

2011-05-22 14:13 UTC #0 lore raw

Hi,

Using USB stick as root device does not work for me. I specify 'root=/dev/sdb1 rootwait' on the kernel commandline, but the kernel does not wait for the USB stick to be scanned and its partitions found. I have a harddisk which is /dev/sda, and this USB stick would be /dev/sdb.

I think blk_lookup_devt returns the block device number even if it does not exist yet, and init/do_mounts.c:473 therefore skips waiting:

        if ((ROOT_DEV == 0) && root_wait) {

due to ROOT_DEV having become non-zero already.

If I use the commandline: 'root=/dev/sdb1 rootdelay=5' then it does mount and boot properly. However, using rootwait seems safer and faster to me, that it's meant for this use case.

Thanks for any pointers,

Micha

Randy Dunlap

2011-05-23 17:14 UTC #1 lore raw

[adding cc: of linux-usb mailing list]

Quoted 14 lines · On Sun, 22 May 2011 16:13:17 +0200 Micha Nelissen wrote:

Hi,
Using USB stick as root device does not work for me. I specify 'root=/dev/sdb1 rootwait' on the kernel commandline, but the kernel does not wait for the USB stick to be scanned and its partitions found. I have a harddisk which is /dev/sda, and this USB stick would be /dev/sdb.
I think blk_lookup_devt returns the block device number even if it does not exist yet, and init/do_mounts.c:473 therefore skips waiting:
        if ((ROOT_DEV == 0) && root_wait) {
due to ROOT_DEV having become non-zero already.

Quoted 8 lines

If I use the commandline: 'root=/dev/sdb1 rootdelay=5' then it does mount and boot properly. However, using rootwait seems safer and faster to me, that it's meant for this use case.
Thanks for any pointers,
Micha
--

---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***

Alan Stern

2011-05-23 17:36 UTC #2 lore raw

Quoted 1 line · Randy Dunlap

[adding cc: of linux-usb mailing list]

Better to ask people familiar with the block layer (CC'ed).

Alan Stern

Quoted 28 lines · On Sun, 22 May 2011 16:13:17 +0200 Micha Nelissen wrote:

Quoted 15 lines
Hi,
Using USB stick as root device does not work for me. I specify 'root=/dev/sdb1 rootwait' on the kernel commandline, but the kernel does not wait for the USB stick to be scanned and its partitions found. I have a harddisk which is /dev/sda, and this USB stick would be /dev/sdb.
I think blk_lookup_devt returns the block device number even if it does not exist yet, and init/do_mounts.c:473 therefore skips waiting:
        if ((ROOT_DEV == 0) && root_wait) {
due to ROOT_DEV having become non-zero already.
Quoted 8 lines
If I use the commandline: 'root=/dev/sdb1 rootdelay=5' then it does mount and boot properly. However, using rootwait seems safer and faster to me, that it's meant for this use case.
Thanks for any pointers,
Micha
--
---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***

Micha Nelissen

author

2011-05-23 18:06 UTC #3 lore raw

Hi all,

Quoted 2 lines · Alan Stern

On Mon, 23 May 2011, Randy Dunlap wrote:
Better to ask people familiar with the block layer (CC'ed).

I found out what happened: I use LILO, and lilo was not passing root=/dev/sdb1 on the commandline, but root=811. However, I didn't see that since on i386 that part had already scrolled off-screen. I found out by accident, due to a user space program trying to parse that, expecting a string, getting a number :-).

Using the following in my lilo.conf:

append="root=/dev/sdb1 rootwait"
instead of

	root=/dev/sdb1

works perfectly. Maybe this information is useful for somebody else; I did not find it using a quick google.

Thanks for your attention.

Micha

Quoted 29 lines

Quoted 27 lines · On Sun, 22 May 2011 16:13:17 +0200 Micha Nelissen wrote:
Quoted 15 lines
Hi,
Using USB stick as root device does not work for me. I specify 'root=/dev/sdb1 rootwait' on the kernel commandline, but the kernel does not wait for the USB stick to be scanned and its partitions found. I have a harddisk which is /dev/sda, and this USB stick would be /dev/sdb.
I think blk_lookup_devt returns the block device number even if it does not exist yet, and init/do_mounts.c:473 therefore skips waiting:
        if ((ROOT_DEV == 0) && root_wait) {
due to ROOT_DEV having become non-zero already.
Quoted 8 lines
If I use the commandline: 'root=/dev/sdb1 rootdelay=5' then it does mount and boot properly. However, using rootwait seems safer and faster to me, that it's meant for this use case.
Thanks for any pointers,
Micha
--
---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***