Re: Quota on tmpfs

[David Holland <dholland-tech%netbsd.org@localhost>]

On Thu, Jul 12, 2012 at 07:14:07PM +0000, David Holland wrote:
 >  > > > How do I enable new quota on a tmpfs?
 >  > > 
 >  > > You don't; tmpfs doesn't support quotas. It could nowadays, but
 >  > > someone has to do the coding :(
 >  > 
 >  > How is the new NetBSD 6 quota system implemented ? I thought it was
 >  > in the VFS layer but apparently it's still filesystem-specific.
 > 
 > It has to be, because the quota state has to, you know, be stored
 > somewhere.

...and to actually answer the question, the fs-independent quota
system is a data model, a client interface, and transport/request
routing code under the covers. Plus the userlevel tools, which use the
client interface.

The fs-dependent quota system takes care of storing the quota
information, storing/maintaining the usage information, enforcement
based on the usage information, and also recovering/restoring
consistency of the usage information after crashing.

It is possible that some of the enforcement logic could be made
fs-independent, but it's probably difficult without knowing how the
filesystem allocates resources. E.g. if you write() to fill in holes
in a file, outside the filesystem it's very difficult to know that
you're increasing your block usage, or for that matter by how much
when indirect blocks are (might be) involved.

-- 
David A. Holland
dholland%netbsd.org@localhost