Re: fs-independent quotas

[Alan Barrett <apb%cequrux.com@localhost>]

On Wed, 19 Oct 2011, David Holland wrote:
>   - the quota key is:
>        the quota *class*
>        the id
>        the quota *type*
>
>   - the quota value is:
>        the configured hard limit
>        the configured soft limit
>        the configured grace period
>        the current usage
>        the current grace expiry time (if any)

This seems sensible.

> 1. A file system type can have or not have support for quotas. If
> there is no support for quotas, nothing else works.
>
> 2. Any given filesystem volume may have or not have quota data on it.
> This is the filesystem code's problem and irrelevant to the
> FS-independent logic.
>
> 3. Any given filesystem volume may be mounted with or without quotas
> enabled. If quotas are not enabled, quota information is not available
> and the quota utilities will not be able to do anything.
>
> 4. Once mounted, quotas can be either on or off. As far as the
> FS-independent code is concerned, quotas being off means only that
> they aren't enforced; that is, with quotas off operations that
> increase usage do not fail with EDQUOT. When quotas are off, quota
> information can still be inspected or updated.

I don't like the names "on" and "off" at level 4.  They are too vague,
and too easily confused with "enabled" or "not enabled" at level 3.

I'd suggest these names:

1. "supported" or "not supported" by the file system format
2. "present" or "not present" in the file system backing store
3. "enabled" or "not enabled" in the mounted file system
4. "enforced" or "not enforced" for the system/user/group/file system/???

I think you might want a fs-independent API to ask the file 
system whether or not quotas are supported or present.  I suppose 
getschemaname answers the "present?" question, but I don't see 
anything that would help a user interface choose whether to 
display a message saying "quotas not supported, tough luck" or 
"quotas not enabled, would you like to enable quotas now?"

--apb (Alan Barrett)