bcache: drop discard sysfs interface

Since discard code is removed, now the sysfs interface to enable discard
is useless. This patch removes the corresponding sysfs entry, and remove
bool variable 'discard' from struct cache as well.

Signed-off-by: Coly Li <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/md/bcache/bcache.h

···
 	 * free_inc: Incoming buckets - these are buckets that currently have
 	 * cached data in them, and we can't reuse them until after we write
 	 * their new gen to disk. After prio_write() finishes writing the new
-	 * gens/prios, they'll be moved to the free list (and possibly discarded
-	 * in the process)
+	 * gens/prios, they'll be moved to the free list.
 	 */
 	DECLARE_FIFO(long, free)[RESERVE_NR];
 	DECLARE_FIFO(long, free_inc);
···
 	 * cpu
 	 */
 	unsigned int		invalidate_needs_gc;
-
-	bool			discard; /* Get rid of? */
 
 	struct journal_device	journal;
 

drivers/md/bcache/super.c

···
 	ca->bdev = file_bdev(bdev_file);
 	ca->sb_disk = sb_disk;
 
-	if (bdev_max_discard_sectors(file_bdev(bdev_file)))
-		ca->discard = CACHE_DISCARD(&ca->sb);
-
 	ret = cache_alloc(ca);
 	if (ret != 0) {
 		if (ret == -ENOMEM)

drivers/md/bcache/sysfs.c

···
 rw_attribute(synchronous);
 rw_attribute(journal_delay_ms);
 rw_attribute(io_disable);
-rw_attribute(discard);
 rw_attribute(running);
 rw_attribute(label);
 rw_attribute(errors);
···
 	sysfs_hprint(bucket_size,	bucket_bytes(ca));
 	sysfs_hprint(block_size,	block_bytes(ca));
 	sysfs_print(nbuckets,		ca->sb.nbuckets);
-	sysfs_print(discard,		ca->discard);
 	sysfs_hprint(written, atomic_long_read(&ca->sectors_written) << 9);
 	sysfs_hprint(btree_written,
 		     atomic_long_read(&ca->btree_sectors_written) << 9);
···
 	if (bcache_is_reboot)
 		return -EBUSY;
 
-	if (attr == &sysfs_discard) {
-		bool v = strtoul_or_return(buf);
-
-		if (bdev_max_discard_sectors(ca->bdev))
-			ca->discard = v;
-
-		if (v != CACHE_DISCARD(&ca->sb)) {
-			SET_CACHE_DISCARD(&ca->sb, v);
-			bcache_write_super(ca->set);
-		}
-	}
-
 	if (attr == &sysfs_cache_replacement_policy) {
 		v = __sysfs_match_string(cache_replacement_policies, -1, buf);
 		if (v < 0)
···
 	&sysfs_block_size,
 	&sysfs_nbuckets,
 	&sysfs_priority_stats,
-	&sysfs_discard,
 	&sysfs_written,
 	&sysfs_btree_written,
 	&sysfs_metadata_written,

drivers/md/bcache/writeback.c

···
 			 * may set BCH_ENABLE_AUTO_GC via sysfs, then when
 			 * BCH_DO_AUTO_GC is set, garbage collection thread
 			 * will be wake up here. After moving gc, the shrunk
-			 * btree and discarded free buckets SSD space may be
-			 * helpful for following write requests.
+			 * btree may be helpful for following write requests.
 			 */
 			if (c->gc_after_writeback ==
 			    (BCH_ENABLE_AUTO_GC|BCH_DO_AUTO_GC)) {