RE: register_blk_dev seems to do nothing during boot for /dev/mtdblock0

Hi,

You (as in "a script/program living on the rootfs") do not need to mount the root to access
the root at boot this is handled by the kernel.
Check root_dev_names[] in init/do_mounts.c (linuxppc-2.4.19-pre6) and check if a reference to mtdblock
is there.
You should see something like
	{"mtdblock", 0x1ff00},
in the root_dev_names[] structure. root_dev_names lists all devices that the kernel can boot the rootfs from.

-----Original Message-----
From: "Callebaut, Benoît" [mailto:benoit.callebaut@barco.com]
Sent: 13. mars 2003 14:30
To: Linuxppc-Embedded (E-mail)
Subject: RE: register_blk_dev seems to do nothing during boot for
/dev/mtdblock0



I tried with both mtdblock0 and mtdblock/0 I doesn't work.
I guess that the right name must be mtdblock0 since the devfs
is mounted
after the root.
So the cramfs filesystem must be already mounted to be able
to mount /devfs.

Correct, but like I said above you do not have to have root mounted to access the root on boot.

But the biggest problem for me is that when I use the standard way,

Standard way?

and when the cramfs filesystem is the root filesystem, the
mounting of the
root
hang in the __wait_on_buffer function called by cramfs_read.

(note __wait_for_buffer is defined in fs/buffer.c and cramfs_read in
/fs/cramfs/inode.c)

How did you generate the cramfs image? If I remember correctly then the utility to
generate the cramfs was not endian safe so generating the image on i386 could cause
problems. Note though that it is a long time since I have generated cramfs image.
I am using entirely jffs2 now. But the booting sequence should be the same..

Assuming that the cramfs image is generated correctly, how do you transfer it to the
flash? Are mtd partitions correctly set up for the flash, i.e. is /dev/mtdblock/0 actually
accessing the cramfs image?

The place where it "blocks" in __wait_on_buffer on the loop
implementing the
waiting.
(same kind of code can be found in Linux Device Drivers 2nd
Edition p.287).
Since this code has nothing to do either with the mtd driver
or the cramfs
and also since I have no problem is to mount the cramfs is it
is not the
root filesystem,
I have no idea to make it working.
I tried to bypass this code (putting the mtdblock driver in the cramfs
driver) but that doesn't work.
VFS complains about the /mtdblock driver He can not find.
Without this hack
It can open the mtd driver.

The lacking of /dev/mtdblock0(or /dev/mtdblock/0) seems not
be a problem for
linux at boot time,

It should not be, at boot time the kernel accesses the flash with the aid of
root_dev_names[], not throught the file systems (which at boot time is not mounted,
you are actually prepareing (I am assuming that the mount process is failing (which might
be wrong assumption ( no I am not a LISP programmer ( 8-))))) to mount it).

devfs_find_handle returns also 0 when I uses the standard
code (I use a
string constant)
The kernel uses the major and minor number to find the root
device. ( see

which has to be defined in root_dev_names[].

super.c)

Regards,

K.D.

-----Original Message-----
From: Kári Davíðsson [mailto:kd@medcare.is]
Sent: Thursday, March 13, 2003 2:22 PM
To: "Callebaut, Benoît"; Linuxppc-Embedded (E-mail)
Subject: RE: register_blk_dev seems to do nothing during boot for
/dev/mtdblock0


Hi,

If you are using devfs, it is called /dev/mtdblock/0 _not_
/dev/mtdblock0.

Do not forget to mount the devfs on boot.

Regards,

K.D.

quoted

-----Original Message-----
From: "Callebaut, Benoît" [mailto:benoit.callebaut@barco.com]
Sent: 13. mars 2003 13:11
To: Linuxppc-Embedded (E-mail)
Subject: register_blk_dev seems to do nothing during boot for
/dev/mtdblock0



I placed the function devfs_find_handle after registering the
filesystem in
the read only block driver for MTD devices.
It returns zero and I never see a mtdblock0 entry appaering
in /dev/ Why
must I use MAKEDEV to do that.
Notes that I can use MAKEDEV in my case since I want to mount
my cramfs
filesystem at boot up.

--------------------------------------------------------------
--------------
------
Benoit Callebaut
Software Development Engineer
Barco | Control Rooms
Noordlaan 5, 8520 Kuurne, Belgium

Tel 	+32(0)56 36 84 28
Fax 	+32(0)56 36 86 05

mailto:benoit.callebaut@barco.com
http://www.barcocontrolrooms.com

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/