Re: [dm-devel] [PATCH v2 2/3] block: reorganize rounding of max_discard_sectors

Paolo Bonzini
2012-07-03T11:47:59Z

Il 03/07/2012 04:49, Vivek Goyal ha scritto:
>> > + /* Zero-sector (unknown) and one-sector granularities are the same. */
>> > + granularity = max(q->limits.discard_granularity >> 9, 1U);
>> > +
>> > /*
>> > * Ensure that max_discard_sectors is of the proper
>> > * granularity
>> > */
>> > max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
>> > + max_discard_sectors = round_down(max_discard_sectors, granularity);
>> > if (unlikely(!max_discard_sectors)) {
>> > /* Avoid infinite loop below. Being cautious never hurts. */
>> > return -EOPNOTSUPP;
>> > - } else if (q->limits.discard_granularity) {
>> > - unsigned int disc_sects = q->limits.discard_granularity >> 9;
>> > -
>> > - max_discard_sectors &= ~(disc_sects - 1);
> This is kind of odd. If discard_granularity is zero, we assume that
> discards are supported and granularity is 1. But if max_discard_sectors
> is zero, we assume discards are disabled. Not sure if we should treat
> max_discard_sectors and discard_granularity in same way or not.

Yes, this keeps the same behavior as before. It is also the one that is
consistent with drivers/scsi/sd.c. sd_config_discard always sets
limits.discard_granularity and then uses limits.max_discard_sectors to
disable discards.

Paolo