new file system (my experiments)

[Kris Kennaway]

Chagin Dmitry wrote:
> Hi
> 
> I experiment resalization of new file system based on tmpfs - shmfs for
> Linux emulation layer. for the beginning has simply copied current source
> codes to compat/lintmps, has compiled a module and tried to mount:
> 
> mount -t lintmpfs lintmpfs /compat/linux/dev/shm
> and has received a panic:
> 
> #11 0xffffffff803b6ade in calltrap ()
>     at /usr/local/root/pub/linux_shmfs/sys/amd64/amd64/exception.S:217
> ---Type <return> to continue, or q <return> to quit---
> #12 0xffffffff802a794b in vfs_filteropt (opts=0x0, legal=0xffffffff808497e0)
>     at /usr/local/root/pub/linux_shmfs/sys/kern/vfs_mount.c:1812
> #13 0xffffffff80847015 in tmpfs_mount (mp=0xffffff0001a3a000,
>     td=0xffffff004dcb56c0)
>     at /usr/local/root/pub/linux_shmfs/sys/modules/lintmpfs/../../compat/lintmpf
>     s/lintmpfs_vfsops.c:206
> #14 0xffffffff802a947f in vfs_donmount (td=0xffffff004dcb56c0, fsflags=0,
>     fsoptions=0xffffff000190e800)
>     at /usr/local/root/pub/linux_shmfs/sys/kern/vfs_mount.c:1010
> #15 0xffffffff802aaa46 in nmount (td=0xffffff004dcb56c0,
>     uap=0xfffffffe7e7fcbf0)
>     at /usr/local/root/pub/linux_shmfs/sys/kern/vfs_mount.c:417
> #16 0xffffffff803d4e47 in syscall (frame=0xfffffffe7e7fcc80)
>     at /usr/local/root/pub/linux_shmfs/sys/amd64/amd64/trap.c:902
> #17 0xffffffff803b6ceb in Xfast_syscall ()
> 
> (kgdb) f 12
> #12 0xffffffff802a794b in vfs_filteropt (opts=0x0, legal=0xffffffff808497e0)
>     at /usr/local/root/pub/linux_shmfs/sys/kern/vfs_mount.c:1812
> 1812    {
> (kgdb) list *0xffffffff802a794b
> 0xffffffff802a794b is in vfs_filteropt (/usr/local/root/pub/linux_shmfs/sys/kern
> /vfs_mount.c:1818).
> 1813            struct vfsopt *opt;
> 1814            char errmsg[255];
> 1815            const char **t, *p, *q;
> 1816            int ret = 0;
> 1817
> 1818            TAILQ_FOREACH(opt, opts, link) {
> 1819                    p = opt->name;
> 1820                    q = NULL;
> 1821                    if (p[0] == 'n' && p[1] == 'o')
> 1822                            q = p + 2;
> (kgdb)
> (kgdb) up
> #13 0xffffffff80847015 in tmpfs_mount (mp=0xffffff0001a3a000,
>     td=0xffffff004dcb56c0)
>     at /usr/local/root/pub/linux_shmfs/sys/modules/lintmpfs/../../compat/lintmpf
> s/lintmpfs_vfsops.c:206
> 206             if (vfs_filteropt(mp->mnt_optnew, lintmpfs_opts))
> (kgdb)
> 
> Problem in that mp->mnt_optnew is 0, but tmpfs works correctly.
> I shall not understand that I have missied...
> 

If you have DEBUG_LOCKS and/or DEBUG_VFS_LOCKS then one of them changes 
the kernel ABI (adds entries to structs somewhere).  You need to either 
add them to the module CFLAGS or use make buildkernel.

Kris