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, 5 insertions, 4 deletions

diff --git a/drivers/cdrom/gdrom.c b/drivers/cdrom/gdrom.c
index 1372763a948f..53f8278e66f7 100644
--- a/drivers/cdrom/gdrom.c
+++ b/drivers/cdrom/gdrom.c
@@ -583,7 +583,8 @@ static int gdrom_set_interrupt_handlers(void)
  */
 static void gdrom_readdisk_dma(struct work_struct *work)
 {
-        int err, block, block_cnt;
+        int block, block_cnt;
+        blk_status_t err;
         struct packet_command *read_command;
         struct list_head *elem, *next;
         struct request *req;
@@ -641,7 +642,7 @@ static void gdrom_readdisk_dma(struct work_struct *work)
                 __raw_writeb(1, GDROM_DMA_STATUS_REG);
                 wait_event_interruptible_timeout(request_queue,
                         gd.transfer == 0, GDROM_DEFAULT_TIMEOUT);
-                err = gd.transfer ? -EIO : 0;
+                err = gd.transfer ? BLK_STS_IOERR : BLK_STS_OK;
                 gd.transfer = 0;
                 gd.pending = 0;
                 /* now seek to take the request spinlock
@@ -670,11 +671,11 @@ static void gdrom_request(struct request_queue *rq)
                         break;
                 case REQ_OP_WRITE:
                         pr_notice("Read only device - write request ignored\n");
-                        __blk_end_request_all(req, -EIO);
+                        __blk_end_request_all(req, BLK_STS_IOERR);
                         break;
                 default:
                         printk(KERN_DEBUG "gdrom: Non-fs request ignored\n");
-                        __blk_end_request_all(req, -EIO);
+                        __blk_end_request_all(req, BLK_STS_IOERR);
                         break;
                 }
         }