Re: [RFC] Draft Linux kernel interfaces for ZBC drives

[Theodore Ts'o <tytso@mit.edu>]

On Tue, Feb 04, 2014 at 02:00:58AM +0000, HanBin Yoon wrote:
> 
> Just a minor point, but I noticed that the specification (14-010r1) had an 
> ordering for these flags in the zone descriptor format (Table 6) in a 
> different way from the above #define's. I thought it might be handy to have 
> these sync up? For example:

Sure, making them line up would mean make it a little easier to
translate from the response from the drive to the Linux kernel
structure.

> >  * If free_sectors_criteria is positive, then return zones that have
> >  * at least that many sectors available to be written.  If it is zero,
> >  * then match all zones.  If free_sectors_criteria is negative, then
> >  * return the zones that match the following criteria:
> >  *
> >  *      -1     Return all read-only zones
> >  *      -2     Return all offline zones
> >  *      -3     Return all zones where the write ptr != the checkpoint ptr
> 
> "all" above for -1/-2/-3 is still limited by (int) max_zones, correct?

Good point, that is what I intended.  We can better clarify this
replacing "Return all..." with "Match all...".

> I was also wondering whether the returned (struct) zone_status'es should 
> have any ordering, e.g., if they should preserve the ordering given by the 
> drive. According to the specification for REPORT ZONES, "The descriptors 
> shall be sorted in ascending order based on the zone start LBA value." If 
> this ordering is preserved, maybe it will help to reduce seek distance 
> (assuming correlation between ascending LBA and going from OD to ID)?

Yes, I was assuming they would be returned in ascending LBA order,
but we should explicitly specify this in the interface specification.

Cheers,

					- Ted