Re: [RFC] vfs generic subtree support

[Dmitry Monakhov <dmonakhov@openvz.org>]

Al Viro <viro@ZenIV.linux.org.uk> writes:

> On Tue, Feb 16, 2010 at 05:01:36PM +0300, Dmitry Monakhov wrote:
>
>> Let's call it "metagroup" id. If you know better (more descriptive) word
>> for this purpose i please make your suggestion.
>> 
>> - Such metagroup may be assigned to inode. And this id is stored on
>>   inode.
>> - It may be inherent from parent, if corresponding flag is set 
>>   on parent dir.
- if inherent flag is not set, then inherent metagroup id
  from mnt_root 
>> - metagroup id may be used by generic quota.
>
> I would probably like to see example with fewer "may" and more details ;-)
> Seriously, what kind of rules and uses for it do you have in mind?  More
> specific example would be nice...
Use-cases:
*Assing maximum disc space consumption for some hierarchy *

  1) Create chroot environment
    # tar  xf chroot_env.tar /var/xxx/chroot
  2) Assign some metagroup id to the chroot content (via not yet
     existent ./metagroup cmd-tool)
    # find /var/xxx/chroot  | xargs ./metagroup --set 1000

  3) Setup quota limits
    # quota-set --type metagroup --blk_soft=1024M blk_hard=1024M /var

  4) Export this tree (it may be more complex)
    # mount /var/xxx/chroot /mnt/chroot -obound

  5)Now we may use this /mnt/chroot as:
    5A) A regular chroot envirement, user is unable to exceed metagroup
        quota, regardless to real available space on /var/
    5B) As a container's (namespace) root. 
    5C) export this /mnt/chroot to nfs server and nfs client can not
        overcome given metagroup quota limit.