Tigran Aivazian writes:
> On Sat, 10 Jun 2000, Alexander Viro wrote:
> > > - although not documented, you need to do kern_mount() before trying
> > Yup.
> > > normal mounts of a FS_SINGLE; perhaps kern_mount()/kern_umount()
> > > should be called automatically in
> > > register_filesystem()/unregister_filesystem()?
> >
> > I don't think so. They are different operations and I'm not too happy
> > about mixing them together. Matter of taste, but...
>
> In get_sb_single() you wrote:
>
> sb = fs_type->kern_mnt->mnt_sb;
> if (!sb)
> BUG();
>
> and it is kern_mount() that initialises type->kern_mnt. So, if one forgot
> to kern_mount a FS_SINGLE filesystem prior to letting userspace try to
> mount(2) it, then it is not the BUG() that we hit but an oops of this
> kind:
>
> Code; c013c6b1 <get_sb_single+59/98> <=====
> 0: 8b 58 1c mov 0x1c(%eax),%ebx <=====
>
> (0x1c being offset of mnt_sb in vfsmount)
>
> i.e. maybe we should really have in get_sb_single():
>
> if (!fs_type->kern_mnt || !(sb = fs_type->kern_mnt->mnt_sb))
> BUG();
>
> I.e. if one forgot to kern_mount then fs_type->kern_mnt will be probably
> left at NULL so one is more likely to follow a NULL pointer via ->kern_mnt
> rather that follow somewhere valid and then find NULL via ->mnt_sb?
>
> Richard, how is it that you actually hit the BUG() above?
Hm. Digging back into my archives, I see I said I got a kernel BUG. So
that means I got a BUG, not an Oops. Perhaps that means that *fs_type
hasn't been initialised to 0, or perhaps that fs_type->kern_mnt gets
initialised elsewhere even when kern_mount() isn't called (and perhaps
kern_mount() just initialises fs_type->kern_mnt->mnt_sb).
Speculations only: I haven't RTFS.
Regards,
Richard....
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