On Thu, 20 Jul 2023, Chaitanya Kulkarni wrote:
> > Index: linux-2.6/drivers/block/brd.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/block/brd.c
> > +++ linux-2.6/drivers/block/brd.c
> > @@ -272,7 +272,8 @@ out:
> >
> > void brd_do_discard(struct brd_device *brd, struct bio *bio)
> > {
> > - sector_t sector, len, front_pad;
> > + bool zero_padding = bio_op(bio) == REQ_OP_WRITE_ZEROES;
> > + sector_t sector, len, front_pad, end_pad;
> >
> > if (unlikely(!discard)) {
> > bio->bi_status = BLK_STS_NOTSUPP;
> > @@ -282,11 +283,22 @@ void brd_do_discard(struct brd_device *b
> > sector = bio->bi_iter.bi_sector;
> > len = bio_sectors(bio);
> > front_pad = -sector & (PAGE_SECTORS - 1);
> > +
> > + if (zero_padding && unlikely(front_pad != 0))
> > + copy_to_brd(brd, page_address(ZERO_PAGE(0)),
> > + sector, min(len, front_pad) << SECTOR_SHIFT);
> > +
>
> Is it possible to create different interface for discard and write
> zeroes ? I think it is a lot of logic adding on one function if everyone
> else is okay please discard my comment ..
Copying code is anti-pattern - it increases code size and it makes it
harder to modify code in the future.
Discard and write-zeroes perform almost the same operation, the only
difference is that write-zeroes needs to zero trailing and leading parts
of boundary pages.
Therefore I think that making one function that performs both discard and
write zeroes is ok.
> > - if (bio_op(bio) == REQ_OP_DISCARD) {
> > + if (bio_op(bio) == REQ_OP_DISCARD ||
> > + bio_op(bio) == REQ_OP_WRITE_ZEROES) {
> > brd_do_discard(brd, bio);
> > goto endio;
> > }
>
> can we please use switch ? unless there is a strong need for if
> which I failed to understand ...
Yes, I can do this change.
> > @@ -355,7 +368,7 @@ MODULE_PARM_DESC(max_part, "Num Minors t
> >
> > static bool discard = false;
> > module_param(discard, bool, 0444);
> > -MODULE_PARM_DESC(discard, "Support discard");
> > +MODULE_PARM_DESC(discard, "Support discard and write zeroes");
> >
>
> write-zeroes and discards are both different req_op and they should have
> a separate module parameter ...
>
> above should be moved to new module parameter write_zeroes, unless there
> is a reason to use one module parameter for both req_op...
Is there some reason why the user might want discard and not want
write-zeroes or vice versa?
What do Christoph and Jens think? Do you think that there should be two
separate parameters too?
Mikulas
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