Re: [PATCH 2/2] Btrfs: do not delete a subvolume which is in a R/O subvolume

[Miao Xie <miaox@cn.fujitsu.com>]

On Mon, 22 Oct 2012 05:57:12 -0600, cwillu wrote:
> On Mon, Oct 22, 2012 at 5:39 AM, Miao Xie <miaox@cn.fujitsu.com> wrote:
>> Step to reproduce:
>>  # mkfs.btrfs <disk>
>>  # mount <disk> <mnt>
>>  # btrfs sub create <mnt>/subv0
>>  # btrfs sub snap <mnt> <mnt>/subv0/snap0
>>  # change <mnt>/subv0 from R/W to R/O
>>  # btrfs sub del <mnt>/subv0/snap0
>>
>> We deleted the snapshot successfully. I think we should not be able to delete
>> the snapshot since the parent subvolume is R/O.
> 
> snap0 isn't read-only in that case, right?  From a user interaction
> standpoint, this seems like it just forces a user to rm -rf rather
> btrfs sub del, which strikes me as a bit ham-handed when all we really
> care about is leaving a (the?) directory entry where snap0 used to be.
> 

I don't think we can identify "btrfs sub del" with "rm -rf", because "rm -rf"
will check the permission of the parent directory of each file/directory which
is going to be deleted, but "btrfs sub del" doesn't do it, it will see all the
file/directory in the subvolume as one, so I think it seems like a special
"rmdir". From this standpoint, deleting a snapshot whose parent subvolume
is readonly should be forbidden.

Thanks
Miao