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

[Kári Davíðsson]

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 at 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 at 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.
>
> > -----Original Message-----
> > From: "Callebaut, Benoît" [mailto:benoit.callebaut at 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 at barco.com
> > http://www.barcocontrolrooms.com
> >
> >
>


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