RAM disk image with offset after kernel

From: Martin Kreiner (martin@boich.de)
Date: Tue Sep 17 2002 - 08:03:02 EST


i'am currently working on a thin-client solution for IBM's 2x00.
with modified bios they are able to load an uncompressed kernel. i would
like to append a RAM disk image as described in
../Documentation/ramdisk.txt but rdev can't handle this magic any more?:

./arch/i386/kernel/setup.c:#define RAMDISK_IMAGE_START_MASK 0x07FF
./arch/i386/kernel/setup.c:#define RAMDISK_PROMPT_FLAG 0x8000
./arch/i386/kernel/setup.c:#define RAMDISK_LOAD_FLAG 0x4000


The usage of the word (two bytes) that "rdev -r" sets in the kernel image
has changed. The low 11 bits (0 -> 10) specify an offset (in 1 k blocks)
of up to 2 MB (2^11) of where to find the RAM disk (this used to be the
size). Bit 14 indicates that a RAM disk is to be loaded, and bit 15
indicates whether a prompt/wait sequence is to be given before trying
to read the RAM disk.


Use "rdev" to set the boot device, RAM disk offset, prompt flag, etc.
For prompt_ramdisk=1, load_ramdisk=1, ramdisk_start=400, one would
have 2^15 + 2^14 + 400 = 49552.

        rdev /dev/fd0 /dev/fd0
        rdev -r /dev/fd0 49552

so i tried :

dd if=my_ramdisk_image of=vmlinux bs=1k seek=my_kernel_size+some_space

and changed in ../arch/i386/kernel/setup.c:

- char c = ' ', *to = command_line, *from = COMMAND_LINE
+ char c = ' ', *to = command_line, *from = strcat(COMMAND_LINE , "

but in ../init/do_mount.c:

if (ext2sb->s_magic == cpu_to_le16(EXT2_SUPER_MAGIC)

failed, so at boot i get:

RAMDISK: Couldn't find valid RAM disk image starting at

what's wrong? Superblock?


martin kreiner

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