block: introduce new block status code type

Currently we use nornal Linux errno values in the block layer, and while
we accept any error a few have overloaded magic meanings.  This patch
instead introduces a new  blk_status_t value that holds block layer specific
status codes and explicitly explains their meaning.  Helpers to convert from
and to the previous special meanings are provided for now, but I suspect
we want to get rid of them in the long run - those drivers that have a
errno input (e.g. networking) usually get errnos that don't know about
the special block layer overloads, and similarly returning them to userspace
will usually return somethings that strictly speaking isn't correct
for file system operations, but that's left as an exercise for later.

For now the set of errors is a very limited set that closely corresponds
to the previous overloaded errno values, but there is some low hanging
fruite to improve it.

blk_status_t (ab)uses the sparse __bitwise annotations to allow for sparse
typechecking, so that we can easily catch places passing the wrong values.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/block/z2ram.c b/drivers/block/z2ram.c
index 968f9e5..41c95c9 100644
--- a/drivers/block/z2ram.c
+++ b/drivers/block/z2ram.c
@@ -74,14 +74,14 @@ static void do_z2_request(struct request_queue *q)
 	while (req) {
 		unsigned long start = blk_rq_pos(req) << 9;
 		unsigned long len  = blk_rq_cur_bytes(req);
-		int err = 0;
+		blk_status_t err = BLK_STS_OK;
 
 		if (start + len > z2ram_size) {
 			pr_err(DEVICE_NAME ": bad access: block=%llu, "
 			       "count=%u\n",
 			       (unsigned long long)blk_rq_pos(req),
 			       blk_rq_cur_sectors(req));
-			err = -EIO;
+			err = BLK_STS_IOERR;
 			goto done;
 		}
 		while (len) {