After trying most of the block devices to boot the kernel under QEMU,
I added few printks around the code that does the mounting.
The function mount_root() in file init/do_mounts.c, mounts the root
file system. Using following code
printk("\n\nmajor=%d minor=%d\n\n", MAJOR(ROOT_DEV), MINOR(ROOT_DEV));
create_dev("/dev/root", ROOT_DEV);
mount_block_root("/dev/root", root_mountflags);
Question 1: Why is it creating a new device file with name /dev/root
and mounting the /dev/root? I am specifying my root device to be
/dev/hda1 as a boot parameter.
In function, added a printk to display the file system the code is
trying to mount
mount_block_root()
{
...
...
for (p = fs_names; *p; p += strlen(p)+1) {
int err = do_mount_root(name, p, flags, root_mount_data);
printk("name=%s fs=%s err=%d\n", name, p, err);
...
...
}
This is the log produced
# qemu-system-arm -M realview-pbx-a9 -kernel clfskernel-2.6.36 -hda
initrd-rootfs.gz -append "console=ttyAMA0 root=/dev/hda1 ro mem=256M"
-m 1024 -nographic
..
..
major=0 minor=0
name=/dev/root fs=ext3 err=-6
VFS: Cannot open root device "hda1" or unknown-block(0,0)
Please append a correct "root=" boot option; here are the available partitions:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
Backtrace:
The error is
#define ENXIO 6 /* No such device or address */
Question 2: Shouldn't this always fail, the major and minor numbers are zero?
Thanks and Regards,
Prasad
On Thu, Dec 9, 2010 at 2:27 PM, Prasad Joshi <prasadjoshi124@xxxxxxxxx> wrote:
> On Thu, Dec 9, 2010 at 1:54 PM, Alexandre Courbot <gnurou@xxxxxxxxx> wrote:
>>> $ qemu-system-arm -M realview-pbx-a9 -kernel clfskernel-2.6.36 -hda
>>> initrd-rootfs.img -append "console=ttyAMA0 root=/dev/hda1 ro mem=256M"
>>> -m 1024 -nographic
>>> ...
>>> VFS: Cannot open root device "hda1" or unknown-block(0,0)
>>> Please append a correct "root=" boot option; here are the available partitions:
>>> Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
>>
>> Yup, no partition are listed, this means that the kernel did not
>> detect the disk. The required block device driver and filesystem must
>> be built into the kernel (i.e. not as modules) or you will not be able
>> to mount access it.
>>
>> In that case I am afraid the link I gave you will not be very helpful
>> - you just need to enable to right device driver. Unless QEmu did not
>> like your disk image, but in that case I guess it would have
>> complained.
>>
>
> It is not complaining about the root disk image. I think I have tried
> all of the block device drivers now :(
> Here is the log
>
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