Re: [PATCH 1/3] block: make sure discard bio is aligned with logical block size

[Ming Lei <ming.lei@redhat.com>]

On Sun, Oct 28, 2018 at 04:49:47PM +0100, Christoph Hellwig wrote:
> On Sun, Oct 28, 2018 at 08:51:31AM +0800, Ming Lei wrote:
> > On Fri, Oct 26, 2018 at 09:44:15AM +0200, Christoph Hellwig wrote:
> > > >  		if (req_sects > UINT_MAX >> 9)
> > > > -			req_sects = UINT_MAX >> 9;
> > > > +			req_sects = (UINT_MAX >> 9) & ~bs_mask;
> > > 
> > > Given that we have this same thing duplicated in write zeroes
> > > what about a documented helper?
> > 
> > IMO, using UINT_MAX & bs_mask is better because it is self-explanatory
> > in the context.
> 
> I don't think it is in any way.  I understand it because I know the
> code, but there is nothing that documents why we do that.

Then how about introducing this helper?

 /*
+ * The max sectors one bio can handle is 'UINT_MAX >> 9' becasue
+ * bvec_iter.bi_size is defined as 'unsigned int', also it has to aligned
+ * to with logical block size which is minimum accepted unit by hardware.
+ */
+static inline unsigned int blk_max_allowed_max_secotrs(struct request_queue *q)
+{
+       return round_down(UINT_MAX, queue_logical_block_size(q)) >> 9;
+}
+
+/*

Thanks,
Ming