RE: register_blk_dev seems to do nothing during boot for /dev/mtd block0

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.

I have this line

quoted

-----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.

quoted

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

Standard way?

By enabling the good options in the kernel config with make xconfig without
trying to change anything in the code

quoted

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?

I had the same question about endianess but since I can access this image
when it is mounted after boot up,
I suppose that the endianess is correct (at least cramfs has no problem with
endianess)

I use my BDI2000 probe to do this, but again after using MAKEDEV on the
board, I can see the /dev/mtdblock0 and access it
without problem.
I tried in the kernel to configure the flash as a 3MByte flash instead of a
4MByte to hide the kernel image and ppcboot
from the driver but that doesn't work better.

quoted

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).

quoted

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[].

quoted

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

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