[Qemu-devel] Qemu Boot failure with /dev/ram0

[Qemu-devel] Qemu Boot failure with /dev/ram0

[Saptarshi Sen]

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Hi,

   I want to use a ram disk as a block device for my kernel.( i am
measuring file io on ram )

   I am trying to boot a kernel from using /dev/ram0. However I am getting
"No root Device found"

   qemu-system-x86_64 -m  8G -hda disk.img -kernel vmlinuz-3.10.0-rc6
-initrd initramfs-3.10.0-rc6.img -append "root=/dev/ram0 selinux=0
enforcing=0 rw" -vnc :0

   My rootfs has a /dev/ram0.


Saptarshi

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Re: [Qemu-devel] Qemu Boot failure with /dev/ram0

[Philipp Hahn]

Hello,

On Monday 16 September 2013 07:40:08 Saptarshi Sen wrote:
>    I want to use a ram disk as a block device for my kernel.( i am
> measuring file io on ram )
> 
>    I am trying to boot a kernel from using /dev/ram0. However I am getting
> "No root Device found"
> 
>    qemu-system-x86_64 -m  8G -hda disk.img -kernel vmlinuz-3.10.0-rc6
> -initrd initramfs-3.10.0-rc6.img -append "root=/dev/ram0 selinux=0
> enforcing=0 rw" -vnc :0

Perhaps you're mixing "Initial*RamFS*" and "Initial*RootDisk*"? Your filename "initramfs" indicates you're going for the former, but your "root=/dev/ram0" is required fror InitRD.

InitRamFS is a (compressed) CPIO archive, which is extracted to a dynamically growing "tmpfs" by the kernel.
InitRD is a (compressed) ext2/3/4/jfs/xfs/whatever filesystem, which is backed by a fixed portion of you RAM; you probably need to explicitly specify a "ramdisk_size=250000" parameter to be large enougth to contain the uncompressed file-system. If the size is too small, you will have a corrupt FS where you also get the error you mention above.

Sincerely
Philipp
-- 
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