[PATCH] loop: remove LO_FLAGS_BH_REMAP

From: Hugh Dickins <hugh@veritas.com>

Jonah Sherman <jsherman@stuy.edu> pointed out back in February how
LO_FLAGS_BH_REMAP is never actually set, since loop_init_xfer only calls
the init for non-0 encryption type.  Fix that or scrap it?  Let's scrap it
for now, that path (hacking values in bio instead of copying data) seems
never to have been tested, and adds to the number of paths through loop:
leave that optimization to some other occasion.

drivers/block/loop.c

@@ -120,12 +120,6 @@ static int transfer_xor(struct loop_device *lo, int cmd, char *raw_buf,
 	return 0;
 }
 
-static int none_status(struct loop_device *lo, const struct loop_info64 *info)
-{
-	lo->lo_flags |= LO_FLAGS_BH_REMAP;
-	return 0;
-}
-
 static int xor_status(struct loop_device *lo, const struct loop_info64 *info)
 {
 	if (info->lo_encrypt_key_size <= 0)
@@ -136,7 +130,6 @@ static int xor_status(struct loop_device *lo, const struct loop_info64 *info)
 struct loop_func_table none_funcs = { 
 	.number = LO_CRYPT_NONE,
 	.transfer = transfer_none,
-	.init = none_status,
 }; 	
 
 struct loop_func_table xor_funcs = { 
@@ -480,14 +473,6 @@ static struct bio *loop_get_buffer(struct loop_device *lo, struct bio *rbh)
 {
 	struct bio *bio;
 
-	/*
-	 * for xfer_funcs that can operate on the same bh, do that
-	 */
-	if (lo->lo_flags & LO_FLAGS_BH_REMAP) {
-		bio = rbh;
-		goto out_bh;
-	}
-
 	/*
 	 * When called on the page reclaim -> writepage path, this code can
 	 * trivially consume all memory.  So we drop PF_MEMALLOC to avoid
@@ -507,8 +492,6 @@ static struct bio *loop_get_buffer(struct loop_device *lo, struct bio *rbh)
 
 	bio->bi_end_io = loop_end_io_transfer;
 	bio->bi_private = rbh;
-
-out_bh:
 	bio->bi_sector = rbh->bi_sector + (lo->lo_offset >> 9);
 	bio->bi_rw = rbh->bi_rw;
 	bio->bi_bdev = lo->lo_device;

include/linux/loop.h

@@ -70,7 +70,6 @@ typedef	int (* transfer_proc_t)(struct loop_device *, int cmd,
  */
 #define LO_FLAGS_DO_BMAP	1
 #define LO_FLAGS_READ_ONLY	2
-#define LO_FLAGS_BH_REMAP	4
 
 #include <asm/posix_types.h>	/* for __kernel_old_dev_t */
 #include <asm/types.h>		/* for __u64 */