Using mtdblock as root device

Using mtdblock as root device

[Robert Kaiser]

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Hi,

I just tried to build a system that uses jffs on /dev/mtdblock0 as root fs.
This didn't work right away because the kernel did not honor the option
"root=/dev/mtdblock0" . This is because mtdblock devices are not listed
in the list of known root devices in the kernel (see "root_dev_names" in file
init/main.c). After applying the attached patch, using mtdblock as rootfs
worked nicely.

Now my question is: is there any particular reason (other than "nobody has
told Linus") why this is not already in the standard kernel ?

If there isn't, should I go ahead and submit my patch to Linus ?


Cheers

Rob


----------------------------------------------------------------
Robert Kaiser                         email: rkaiser@sysgo.de
SYSGO RTS GmbH
Am Pfaffenstein 14                    phone: (49) 6136 9948-762
D-55270 Klein-Winternheim / Germany   fax:   (49) 6136 9948-10

[-- Attachment #2: patch-mtdblock-root --]
[-- Type: text/plain, Size: 656 bytes --]

--- linux/init/main.c.orig	Thu Jan  4 05:45:26 2001
+++ linux/init/main.c	Tue Mar  6 12:57:00 2001
@@ -273,6 +273,24 @@
 #ifdef CONFIG_NFTL
 	{ "nftla", 0x5d00 },
 #endif
+#ifdef CONFIG_MTD
+	{ "mtdblock0", 0x1f00 },
+	{ "mtdblock1", 0x1f01 },
+	{ "mtdblock2", 0x1f02 },
+	{ "mtdblock3", 0x1f03 },
+	{ "mtdblock4", 0x1f04 },
+	{ "mtdblock5", 0x1f05 },
+	{ "mtdblock6", 0x1f06 },
+	{ "mtdblock7", 0x1f07 },
+	{ "mtdblock8", 0x1f08 },
+	{ "mtdblock9", 0x1f09 },
+	{ "mtdblock10", 0x1f0a },
+	{ "mtdblock11", 0x1f0b },
+	{ "mtdblock12", 0x1f0c },
+	{ "mtdblock13", 0x1f0d },
+	{ "mtdblock14", 0x1f0e },
+	{ "mtdblock15", 0x1f0f },
+#endif
 	{ NULL, 0 }
 };
 

Re: Using mtdblock as root device

[Robert Kaiser]

Hi,

On Die, 06 Mär 2001 you wrote:
> It's been submitted many many times. If you do submit it again, please add 
> nftl[bcd] and ftl[abcd] too, and I don't think you actually need anything 
> more than
> 	{"mtdblock", 0x1f00},
> 
> for the mtdblock devices, because they're handled just like partitions.

Hmm, I for one have two mtd devices on my platform, both of which I'd like
to be able to use as root device. But I agree that 16 is probably a bit
overkill. How about:

	{"mtdblock0", 0x1f00},
	{"mtdblock1", 0x1f01},
or:
	{"mtdblock", 0x1f00},
	{"mtdblock0", 0x1f00},
	{"mtdblock1", 0x1f01},

Rob

----------------------------------------------------------------
Robert Kaiser                         email: rkaiser@sysgo.de
SYSGO RTS GmbH
Am Pfaffenstein 14                    phone: (49) 6136 9948-762
D-55270 Klein-Winternheim / Germany   fax:   (49) 6136 9948-10


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RE: Using mtdblock as root device

[Vipin Malik]

>Now my question is: is there any particular reason (other than "nobody
>has told Linus") why this is not already in the standard kernel ?


because it's easier to do a
$rdev <your kernel image here> /dev/mtdblock0 before installing
the kernel with lilo. You don't need to pass any root kernel
line parameters then.

You can even boot a compressed root file system this way by
passing the bit LOAD_RAMDISK=1, the RAMDISK_OFFSET=<your offset in
1k from the start of your root device>. See the bootdisk
howto.

Additionally, You have to go and hack the rd.c code in drivers/block/rc.c to
remove the check to see that the boot device for compressed f/s
is a floppy.

As one additional matter you have to add a call to rd_load() just
before mount_root() in init/main.c so that the ramdisk loading code
runs *after* the mtdblock device has been registered.

Go back in the archives a few weeks. There was quite a bit
discussion re. this matter. I've found all these problems before :)

There's quite a big update to the HOWTO pending that I'll commit
as soon as I get some time (that includes all this stuff and
some corrections). There is a bigger power fail issue
in jffs1 that's hogging all my time right now.

Vipin


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RE: Using mtdblock as root device

[Robert Kaiser]

On Die, 06 Mär 2001 you wrote:
> >Now my question is: is there any particular reason (other than "nobody
> >has told Linus") why this is not already in the standard kernel ?
> 
> 
> because it's easier to do a
> $rdev <your kernel image here> /dev/mtdblock0 before installing
> the kernel with lilo. You don't need to pass any root kernel
> line parameters then.

I'd say since the kernel does support a "root=..." option it might as well
support it for all possible devices rather than just a selection of them.

But that's probably a discussion to be held in linux-kernel.

Rob


----------------------------------------------------------------
Robert Kaiser                         email: rkaiser@sysgo.de
SYSGO RTS GmbH
Am Pfaffenstein 14                    phone: (49) 6136 9948-762
D-55270 Klein-Winternheim / Germany   fax:   (49) 6136 9948-10


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Re: Using mtdblock as root device

[David Woodhouse]

rob@sysgo.de said:
>  I'd say since the kernel does support a "root=..." option it might as
> well support it for all possible devices rather than just a selection
> of them.

I agree. The patch has been submitted many times. I'll resubmit it next 
time I bother - actually it may already be in -ac patches.

--
dwmw2




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Re: Using mtdblock as root device

[David Schleef]

On Tue, Mar 06, 2001 at 02:37:48PM +0100, Robert Kaiser wrote:
> Hi,
> 
> On Die, 06 Mär 2001 you wrote:
> > It's been submitted many many times. If you do submit it again, please add 
> > nftl[bcd] and ftl[abcd] too, and I don't think you actually need anything 
> > more than
> > 	{"mtdblock", 0x1f00},
> > 
> > for the mtdblock devices, because they're handled just like partitions.
> 
> Hmm, I for one have two mtd devices on my platform, both of which I'd like
> to be able to use as root device. But I agree that 16 is probably a bit
> overkill. How about:
> 
> 	{"mtdblock0", 0x1f00},
> 	{"mtdblock1", 0x1f01},
> or:
> 	{"mtdblock", 0x1f00},
> 	{"mtdblock0", 0x1f00},
> 	{"mtdblock1", 0x1f01},


Just {"mtdblock", 0x1f00} will suffice, because any number
appended will be converted to an integer and be added to the
base number given.

Check the implementation of name_to_kdev_t in init/main.c for
details.



dave...



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