> On 4/18/21 10:49 PM, Changheun Lee wrote:
> >>> @@ -167,6 +168,7 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
> >>> max_sectors = round_down(max_sectors,
> >>> limits->logical_block_size >> SECTOR_SHIFT);
> >>> limits->max_sectors = max_sectors;
> >>> + limits->bio_max_bytes = max_sectors << SECTOR_SHIFT;
> >>>
> >>> q->backing_dev_info->io_pages = max_sectors >> (PAGE_SHIFT - 9);
> >>> }
> >>
> >> Can the new shift operation overflow? If so, how about using
> >> check_shl_overflow()?
> >
> > Actually, overflow might be not heppen in case of physical device.
> > But I modified as below. feedback about this.
> >
> > @@ -168,6 +169,9 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
> > limits->logical_block_size >> SECTOR_SHIFT);
> > limits->max_sectors = max_sectors;
> >
> > + limits->bio_max_bytes = check_shl_overflow(max_sectors, SECTOR_SHIFT,
> > + &limits->bio_max_bytes) ? UINT_MAX : max_sectors << SECTOR_SHIFT;
> > +
> > q->backing_dev_info->io_pages = max_sectors >> (PAGE_SHIFT - 9);
> > }
> > EXPORT_SYMBOL(blk_queue_max_hw_sectors);
>
> If no overflow occurs, check_shl_overflow() stores the result in the
> memory location the third argument points at. So the above expression
> can be simplified into the following:
>
> if (check_shl_overflow(max_sectors, SECTOR_SHIFT, &limits->bio_max_bytes)) {
> limits->bio_max_bytes = UINT_MAX;
> }
OK. No problem. It might be more readable.
>
> >>> diff --git a/include/linux/bio.h b/include/linux/bio.h
> >>> index d0246c92a6e8..e5add63da3af 100644
> >>> --- a/include/linux/bio.h
> >>> +++ b/include/linux/bio.h
> >>> @@ -106,6 +106,8 @@ static inline void *bio_data(struct bio *bio)
> >>> return NULL;
> >>> }
> >>>
> >>> +extern unsigned int bio_max_size(struct bio *bio);
> >>
> >> You may want to define bio_max_size() as an inline function in bio.h
> >> such that no additional function calls are introduced in the hot path.
> >
> > I tried, but it is not easy. because request_queue structure of blkdev.h
> > should be referred in bio.h. I think it's not good to apply as a inline function.
>
> Please don't worry about this. Inlining bio_max_size() is not a big
> concern to me.
>
> Thanks,
>
> Bart.
I think removing of UINT_MAX setting in blk_stack_limits() might be good.
Because default queue limits for stacking device will be set in
blk_set_stacking_limits(), and blk_set_default_limits() will be called
automatically. So setting of UINT_MAX in blk_stack_limits() is not needed.
And setting in blk_stack_limits() can overwrite bio_max_bytes as a default
after stacking driver set to proper bio_max_bytes value.
Thanks,
Changheun Lee.
