LimHD:Fuse

FUSE

As it turns out, there are at least two FUSE filesystems that sits on libdvdread / libdvdcss. I could use one of those, or a more raw one that only uses libdvdcss. However, first we will need FUSE compiled, and that is not easy. It seems only Fuse-1.4 will compile against such an old kernel. Most Fuse filesystems will not work against the old FUSE.

I have tried a few versions of FUSE.

Fuse-2.0b from [[1]]

uclibc[/tmp]# insmod fuse.ko
Using fuse.ko
insmod: unresolved symbol match_octal
insmod: unresolved symbol page_cache_release
insmod: unresolved symbol sema_init
insmod: unresolved symbol match_token
insmod: unresolved symbol BUG_ON
insmod: unresolved symbol down
insmod: unresolved symbol down_interruptible
insmod: unresolved symbol down_trylock
insmod: unresolved symbol match_int
insmod: unresolved symbol grab_cache_page
insmod: unresolved symbol up
insmod: unresolved symbol test_bit

Fuse-2.5.3:

uclibc[/tmp]# insmod fuse.o 
Using fuse.o
insmod: unresolved symbol page_cache_release
insmod: unresolved symbol get_user_pages
insmod: unresolved symbol grab_cache_page

Fuse-1.4:

uclibc[/tmp]# insmod fuse.o
Using fuse.o
insmod: unresolved symbol page_cache_release
insmod: unresolved symbol BUG_ON
insmod: unresolved symbol grab_cache_page

As it happens, grab_cache_page call can be replaced by a find_get_page. I have not found a replacement for page_cache_release but as a proof of concept I can go without it (and leak memory).

get_user_pages would be trickiest in 2.5.3, otherwise 1.4 should run if the BUG_ON thing isn't hard.

Trying Fuse

Ok tried 2.5.3 and patched my way around things with some serious hacks:

uclibc[/tmp]# insmod fuse-25.o
Using fuse-25.o
uclibc[/tmp]# lsmod
Module                  Size  Used by    Tainted: P
fuse-25                25664   0 (unused)

uclibc[/tmp]# ./hello-25 /mnt/USB2 -d -s &
25157

But unfortunately df shows no mounts, and there is nothing to see in there. Oh well. It is possible the userland patches never gets to the kernel, as we can't daemonize, nor fork.

It is basically due to pthreads as it replaced vfork and blocks it all. Porting fuse not to be multi-threaded, and changing it to use /tmp/dev/fuse since /dev/ is read-only:

uclibc[/tmp]# dmesg
fuse init (API version 7.5)
fuse distribution version: 2.5.3

uclibc[/tmp]# mknod /tmp/dev/fuse -m 0666 c 10 229
uclibc[/tmp]# ./hello-25 /tmp/mnt -d -s
I am HERE
ibefore parsing
before mount
in mount, before socketpair
before vfork
after vfork 0
executing fusermount
after vfork 262
Common 0x90ec6028

.. and it panics.. so .. shame I can't read the output from "dmesg" before then :)

Retrying Fuse-2.5.3

Fresh start, from compiling. Top level configure:

./configure CFLAGS="-DPATH_MAX=4096 -DMAX_LFS_FILESIZE=0x7fffffffffffffff -DFUSE_DEV_NEW=\"/tmp/dev/fuse\"" LDFLAGS=-Wl,-elf2flt --host=arm-elf --enable-static --enable-kernel-module --with-kernel=/home/lundman/uClinux-2.4
vi libtool
#version_type=none => =linux

Lots of small changes in .C, Makefile.am and Makefiles in general. Mostly to take out all multi-threaded things.

The do the same for kernel/ directory, but notice that the Makefile is not generated correctly.

vi kernel/Makefile
#CC=arm-elf-gcc
#LD=arm-elf-ld

And compile that. The first error we get is:

inode.c:584: error: unknown field `alloc_inode" specified in initializer
inode.c:584: warning: initialization from incompatible pointer type
inode.c:585: error: unknown field `destroy_inode" specified in initializer
inode.c:585: warning: initialization from incompatible pointer type

Basically, around 2.4.20 - 2.4.24 kernel versions, they added support to alloc_inode inside the super_operation structure. Without that we are stuck. However, the same patch [[2]] also define a new function called inode_init_once.

# grep inode_init_once /proc/ksyms
900ddcf8 inode_init_once

So the Lim kernel has this patch. We need to add it to our kernel tree.

vi +871 /home/lundman/uClinux-2.4/include/linux/fs.h
struct super_operations {
+   	struct inode *(*alloc_inode)(struct super_block *sb);
+	void (*destroy_inode)(struct inode *);
+
 	void (*read_inode) (struct inode *);

and suddenly it all compiles. Here it comes, loading the module will reveal the same missing functions:

uclibc[/tmp]# insmod /mnt/smbfs1/fuse.o
Using /mnt/smbfs1/fuse.o
insmod: unresolved symbol page_cache_release
insmod: unresolved symbol get_user_pages
insmod: unresolved symbol grab_cache_page