Miles Bader wrote:
>Jeff Garzik <jgarzik@pobox.com> writes:
>
>
>>I'm not saying that initramfs will do
>>this out of the box :) but going from initramfs to "initromfs" should
>>not be a huge leap...
>>
>>
>
>Do you mean by putting the `internal' format that initramfs normally
>uses in RAM, in ROM, and skip the initial decompression step?
>
>Or do you mean have it somehow avoid copying the data areas of the cpio
>stream (i.e. store pointers from the tree-in-ram to the actual data
>blocks in ROM).
>
>I guess the latter sounds cleaner... it would also have the advantage
>that you could have a tree with the bulk of data in ROM, but which
>allowed new files to be written (which would be stored in RAM).
>
>
Well, Linux wants file data in pages, so you would need to be able to
get your kernel to point to page-aligned ROM regions. Otherwise you are
stuck with the same issues as fs/romfs or fs/cramfs or most other Linux
filesystems -- you gotta copy the data into a RAM page before the Linux
VFS will look at it[1]. For the initramfs cpio image itself, it can
either piggyback inside the kernel image, or be loaded separately via
bootloader, from ROM, or some other magic means. Unpacking [what is
essentially] pointers into the ROM would probably involve custom
userland code in an initramfs which mounts and populates a ROM-based
filesystem.
So one way or another you can have all of _your own_ data in ROM, but I
don't want to paint too rosy a picture -- if you want to be smarter than
fs/romfs is now, it will take some additional work. And of course the
ramfs-based rootfs will still be needed as the underlying writable fs.
Jeff
[1] or you can create your own file_operations and eliminate this
restriction... with a bunch of ROM-specific custom code that totally
bypasses the pagecache
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This archive was generated by hypermail 2b29 : Thu Oct 31 2002 - 22:00:47 EST