On 5/20/24 03:20, Nitesh Shetty wrote:
+ if (blk_rq_nr_phys_segments(req) != BLK_COPY_MAX_SEGMENTS)
+ return status;
Why is this check necessary?
+ /*
+ * First bio contains information about destination and last bio
+ * contains information about source.
+ */
Please check this at runtime (WARN_ON_ONCE()?).
+ __rq_for_each_bio(bio, req) {
+ if (seg == blk_rq_nr_phys_segments(req)) {
+ sector_in = bio->bi_iter.bi_sector;
+ if (rem != bio->bi_iter.bi_size)
+ return status;
+ } else {
+ sector_out = bio->bi_iter.bi_sector;
+ rem = bio->bi_iter.bi_size;
+ }
+ seg++;
+ }
_rq_for_each_bio() iterates over the bios in a request. Does a copy
offload request always have two bios - one copy destination bio and
one copy source bio? If so, is 'seg' a bio counter? Why is that bio
counter compared with the number of physical segments in the request?
+ trace_nullb_copy_op(req, sector_out << SECTOR_SHIFT,
+ sector_in << SECTOR_SHIFT, rem);
+
+ spin_lock_irq(&nullb->lock);
+ while (rem > 0) {
+ chunk = min_t(size_t, nullb->dev->blocksize, rem);
+ offset_in = (sector_in & SECTOR_MASK) << SECTOR_SHIFT;
+ offset_out = (sector_out & SECTOR_MASK) << SECTOR_SHIFT;
+
+ if (null_cache_active(nullb) && !is_fua)
+ null_make_cache_space(nullb, PAGE_SIZE);
+
+ t_page_in = null_lookup_page(nullb, sector_in, false,
+ !null_cache_active(nullb));
+ if (!t_page_in)
+ goto err;
+ t_page_out = null_insert_page(nullb, sector_out,
+ !null_cache_active(nullb) ||
+ is_fua);
+ if (!t_page_out)
+ goto err;
+
+ in = kmap_local_page(t_page_in->page);
+ out = kmap_local_page(t_page_out->page);
+
+ memcpy(out + offset_out, in + offset_in, chunk);
+ kunmap_local(out);
+ kunmap_local(in);
+ __set_bit(sector_out & SECTOR_MASK, t_page_out->bitmap);
+
+ if (is_fua)
+ null_free_sector(nullb, sector_out, true);
+
+ rem -= chunk;
+ sector_in += chunk >> SECTOR_SHIFT;
+ sector_out += chunk >> SECTOR_SHIFT;
+ }
+
+ status = 0;
+err:
+ spin_unlock_irq(&nullb->lock);
In the worst case, how long does this loop disable interrupts?
+TRACE_EVENT(nullb_copy_op,
+ TP_PROTO(struct request *req,
+ sector_t dst, sector_t src, size_t len),
+ TP_ARGS(req, dst, src, len),
+ TP_STRUCT__entry(
+ __array(char, disk, DISK_NAME_LEN)
+ __field(enum req_op, op)
+ __field(sector_t, dst)
+ __field(sector_t, src)
+ __field(size_t, len)
+ ),
Isn't __string() preferred over __array() since the former occupies less space
in the trace buffer?
Thanks,
Bart.
