Date: Tue, 8 Aug 2017 17:40:10 +0200
From: Willy Tarreau <w@1wt.eu>
To: Thomas Meyer <thomas@m3y3r.de>
Cc: rob@landley.net, linux-kernel@vger.kernel.org
Subject: Re: INITRAMFS_SOURCE broken by
 6e19eded3684dc184181093af3bff2ff440f5b53?
Message-ID: <20170808154010.GB27774@1wt.eu>
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 <20170808131819.GA15596@localhost.localdomain>
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On Tue, Aug 08, 2017 at 03:18:19PM +0200, Thomas Meyer wrote:
> On Tue, Aug 08, 2017 at 02:04:42PM +0200, Willy Tarreau wrote:
> > Hi Thomas,
> > 
> > On Tue, Aug 08, 2017 at 01:46:25PM +0200, Thomas Meyer wrote:
> > > Hi,
> > > 
> > > did the commit 6e19eded3684dc184181093af3bff2ff440f5b53 break a linux kernel
> > > build with an included ramdisk?
> > > 
> > > As fas as I understand you must expliclity add rootfstype=ramfs to the kernel
> > > command line to boot from the included ramfsdisk?
> > > 
> > > bug or feature?
> > 
> > Strange, I'm running my kernels with the modules packaged inside the initramfs
> > and never met this problem even after this commit (my 4.9 kernels are still
> > packaged this way and run fine). And yes, I do have TMPFS enabled. I can't
> > tell whether tmpfs or ramfs was used however given that at this level I don't
> > have all the tools available to report the FS type (and proc says "rootfs").
> > Are you sure you're not missing anything ?
> Pretty much I miss something!
> 
> I see that the embedded ramdisk is populated in populate_rootfs()
> without any errors.
> But later it fails in mount_root -> mount_block_root with:
> 
> [   27.070000] VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
> [   27.070000] Please append a correct "root=" boot option; here are the available partitions:
> [   27.070000] DEBUG_BLOCK_EXT_DEVT is enabled, you need to specify explicit textual name for "root=" boot option.
> [   27.070000] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
> 
> but adding rootfstype=ramfs seems to end up with an empty ramfs?!

It would be nice to ensure that your initramfs is really packaged within
the kernel (try to see if adding a large file to it changes the bzImage
size). Maybe it's really empty and the problem happens during the build
and not at boot.

Willy