Re: [PATCH 2/3] change libfs sb creation routines to avoid collisions with their root inodes

[Jeff Layton <jlayton@poochiereds.net>]

Eric Sandeen wrote:
> Christoph Hellwig wrote:
>
>>>  		return -ENOMEM;
>>> +	/* set to high value to try and avoid collisions with loop below */
>>> +	inode->i_ino = 0xffffffff;
>>> +	insert_inode_hash(inode);
>> This is odd.  Can't we just add some constant base to the loop below?
>>
> I thought the same thing, but Jeff pointed out that
> nfsctl_transaction_write does ops based on inode numbers, and they maybe
> can't move around?
>
>         rv =  write_op[ino](file, data, size);
>
> However, nfsd's call to simple_fill_super already sends in a set of
> files starting at inode 2:
>
> enum {
>         NFSD_Root = 1,
>         NFSD_Svc,
> ...
>
>         static struct tree_descr nfsd_files[] = {
>                 [NFSD_Svc] = {".svc", &transaction_ops, S_IWUSR},
> ...
>         return simple_fill_super(sb, 0x6e667364, nfsd_files);
>
> which does...
>
>       for (i = 0; !files->name || files->name[0]; i++, files++) {
>                 if (!files->name)
>                         continue;
> ...
>                 inode->i_ino = i;
>
> So I think it's already expecting the root inode at one, and the other
> files starting at 2?
>

Very interesting -- I saw that nfsctl depended on certain values for i_ino,
but I didn't notice that it had reserved the first slot for NFSD_Root. The
only other caller of simple_fill_super that seems to depend on the inode
numbers is selinuxfs, and that one has this:

enum sel_inos {
        SEL_ROOT_INO = 2,

...so it looks like we can probably use 1 for the root inode (though we might
want to fix selinuxfs to set SEL_ROOT_INO = 1). I'll have a closer look to be
sure that this is all correct and respin this patch since that seems like it
would be less magic-number-y.

Thanks,
Jeff
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