[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Thierry Bultel]

Hi,

When booting with an initrd of type "ext2", as it is the case when using 
a generated ISO image,
the kernel (a 3.2.21 in my case) does not automagically create the 
"/dev/null" and "dev/console" entries,
whereas it does when using a cpio.

Would the solution be to always have these inodes created in 
'device_table.txt' ?
(Works in my case, I do not plan to use the static table)

Or change the ISO generation for using cpio instead of ext2 ?

Thanks
Thierry

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[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Richard Braun]

On Tue, Oct 16, 2012 at 04:16:48PM +0200, Thierry Bultel wrote:
> Would the solution be to always have these inodes created in
> 'device_table.txt' ?
> (Works in my case, I do not plan to use the static table)

The devtmpfs "file system" is usually a better approach.

-- 
Richard Braun

[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Thierry Bultel]

Le 16/10/2012 16:23, Richard Braun a ?crit :
> On Tue, Oct 16, 2012 at 04:16:48PM +0200, Thierry Bultel wrote:
>> Would the solution be to always have these inodes created in
>> 'device_table.txt' ?
>> (Works in my case, I do not plan to use the static table)
> The devtmpfs "file system" is usually a better approach.
>
I have CONFIG_TMPFS and , and CONFIG_DEVTMPFS_MOUNT, and it works with 
everything but initrd of type "ext2"

I am thus asking 2 questions to myself
1) Why does the ISO image imply an ext2 initrd , instead of a cpio ?
2) Why does ext2 not work with devtmpfs (the answer is likely somewhere 
in the kernel sources and I will take a look as well) ?

Regards
Thierry
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[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Richard Braun]

On Tue, Oct 16, 2012 at 06:15:36PM +0200, Thierry Bultel wrote:
> 2) Why does ext2 not work with devtmpfs (the answer is likely
> somewhere in the kernel sources and I will take a look as well) ?

A common mistake is forgetting to select the "mount devtmpfs at boot
time" option (CONFIG_DEVTMPFS_MOUNT).

-- 
Richard Braun

[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Thomas Petazzoni]

Dear Richard Braun,

On Tue, 16 Oct 2012 18:28:25 +0200, Richard Braun wrote:
> On Tue, Oct 16, 2012 at 06:15:36PM +0200, Thierry Bultel wrote:
> > 2) Why does ext2 not work with devtmpfs (the answer is likely
> > somewhere in the kernel sources and I will take a look as well) ?
> 
> A common mistake is forgetting to select the "mount devtmpfs at boot
> time" option (CONFIG_DEVTMPFS_MOUNT).

Yes, but Thierry explicitly said he enabled this option, re-read the
e-mail you're replying to :)

Maybe the devtmpfs mounting done by CONFIG_DEVTMPFS_MOUNT does not take
place when an initrd is used? I honestly don't know, I don't use initrd
personally.

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com

[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Richard Braun]

On Tue, Oct 16, 2012 at 07:27:00PM +0200, Thomas Petazzoni wrote:
> Yes, but Thierry explicitly said he enabled this option, re-read the
> e-mail you're replying to :)

Woah, right sorry, time to sleep. Good luck.

-- 
Richard Braun

[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Peter Korsgaard]

>>>>> "Thomas" == Thomas Petazzoni <thomas.petazzoni@free-electrons.com> writes:

Hi,


 Thomas> Maybe the devtmpfs mounting done by CONFIG_DEVTMPFS_MOUNT does
 Thomas> not take place when an initrd is used? I honestly don't know, I
 Thomas> don't use initrd personally.

I also don't use initrd's, but it's atleast not done for initramfs
(which is why we have the pre-init script in fs/cpio/init).

-- 
Bye, Peter Korsgaard

[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Arnout Vandecappelle]

On 16/10/12 16:16, Thierry Bultel wrote:
> When booting with an initrd of type "ext2", as it is the case when using a generated ISO image,

  ISO?

> the kernel (a 3.2.21 in my case) does not automagically create the "/dev/null" and "dev/console" entries,
> whereas it does when using a cpio.

  The kernel doesn't, but buildroot does.  We copy fs/cpio/init to /init
for cpio (and initramfs) archives, because those are the ones that are
normally used for initrd.

  You can copy fs/cpio/init to /init in your post-build script, if you like.


> Would the solution be to always have these inodes created in 'device_table.txt' ?
> (Works in my case, I do not plan to use the static table)

  Not really: the kernel doesn't automount devtmps for initrd.

> Or change the ISO generation for using cpio instead of ext2 ?

  There's no point in using ext2 for initrd, it just adds overhead.
So yes, switch to cpio.

  Oh, now I see your point with the iso image: fs/iso9660 uses an ext2
initrd...  Hm, that seems like a bad idea.  Someone should rewrite that.

  Regards,
  Arnout
-- 
Arnout Vandecappelle                               arnout at mind be
Senior Embedded Software Architect                 +32-16-286540
Essensium/Mind                                     http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium                BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint:  7CB5 E4CC 6C2E EFD4 6E3D A754 F963 ECAB 2450 2F1F

[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Thierry Bultel]

Le 16/10/2012 18:09, Arnout Vandecappelle a ?crit :
> On 16/10/12 16:16, Thierry Bultel wrote:
>> When booting with an initrd of type "ext2", as it is the case when
>> using a generated ISO image,
>
>  ISO?
>
>> the kernel (a 3.2.21 in my case) does not automagically create the
>> "/dev/null" and "dev/console" entries,
>> whereas it does when using a cpio.
>
>  The kernel doesn't, but buildroot does.  We copy fs/cpio/init to /init
> for cpio (and initramfs) archives, because those are the ones that are
> normally used for initrd.
>
>  You can copy fs/cpio/init to /init in your post-build script, if you
> like.
>
>
>> Would the solution be to always have these inodes created in
>> 'device_table.txt' ?
>> (Works in my case, I do not plan to use the static table)
>
>  Not really: the kernel doesn't automount devtmps for initrd.
>
>> Or change the ISO generation for using cpio instead of ext2 ?
>
>  There's no point in using ext2 for initrd, it just adds overhead.
> So yes, switch to cpio.
>
>  Oh, now I see your point with the iso image: fs/iso9660 uses an ext2
> initrd...  Hm, that seems like a bad idea.  Someone should rewrite that.

FYI, I have hacked into "iso9660.mk"

diff -r1.1.1.1 iso9660.mk
18c18
< $(BINARIES_DIR)/rootfs.iso9660: host-cdrkit host-fakeroot linux
rootfs-ext2 grub
---
> $(BINARIES_DIR)/rootfs.iso9660: host-cdrkit host-fakeroot linux
rootfs-cpio grub
22a23

25c26
<     cp $(BINARIES_DIR)/rootfs.ext2 $(ISO9660_TARGET_DIR)/initrd
---
>     cp $(BINARIES_DIR)/rootfs.cpio $(ISO9660_TARGET_DIR)/initrd

and it works perfectly without having to use the "device_table_dev.txt"

The other thing that is missing here is that the iso9660 build does not
support the grub splashscreen.

>
>  Regards,
>  Arnout

[Buildroot] no /dev/console; /dev/null when booting with initrd of type 'ext2'

[Thomas Petazzoni]

Dear Thierry Bultel,

On Wed, 17 Oct 2012 14:04:07 +0200, Thierry Bultel wrote:

> FYI, I have hacked into "iso9660.mk"
> 
> diff -r1.1.1.1 iso9660.mk
> 18c18
> < $(BINARIES_DIR)/rootfs.iso9660: host-cdrkit host-fakeroot linux
> rootfs-ext2 grub
> ---
> > $(BINARIES_DIR)/rootfs.iso9660: host-cdrkit host-fakeroot linux
> rootfs-cpio grub
> 22a23
> 
> 25c26
> <     cp $(BINARIES_DIR)/rootfs.ext2 $(ISO9660_TARGET_DIR)/initrd
> ---
> >     cp $(BINARIES_DIR)/rootfs.cpio $(ISO9660_TARGET_DIR)/initrd
> 
> and it works perfectly without having to use the
> "device_table_dev.txt"

Could you send a proper Git patch for that? See
http://elinux.org/Buildroot_how_to_contribute.

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com