block: add centralize REQ_OP_XXX to string helper [Linux 5.3]

This Linux kernel change "block: add centralize REQ_OP_XXX to string helper" is included in the Linux 5.3 release. This change is authored by Chaitanya Kulkarni <chaitanya.kulkarni [at] wdc.com> on Thu Jun 20 10:59:16 2019 -0700. The commit for this change in Linux stable tree is e47bc4e (patch).

block: add centralize REQ_OP_XXX to string helper

In order to centralize the REQ_OP_XXX to string conversion which can be
used in the block layer and different places in the kernel like f2fs,
this patch adds a new helper function along with an array similar to the
one present in the blk-mq-debugfs.c.

We keep this helper functionality centralize under blk-core.c instead of
blk-mq-debugfs.c since blk-core.c is configured using CONFIG_BLOCK and
it will not be dependent on blk-mq-debugfs.c which is configured using
CONFIG_BLK_DEBUG_FS.

Next patch adjusts the code in the blk-mq-debugfs.c with newly
introduced helper.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

There are 39 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 block/blk-core.c       | 36 ++++++++++++++++++++++++++++++++++++
 include/linux/blkdev.h |  3 +++
 2 files changed, 39 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index c97da29..129204d 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -120,6 +120,42 @@ void blk_rq_init(struct request_queue *q, struct request *rq)
 }
 EXPORT_SYMBOL(blk_rq_init);

+#define REQ_OP_NAME(name) [REQ_OP_##name] = #name
+static const char *const blk_op_name[] = {
+   REQ_OP_NAME(READ),
+   REQ_OP_NAME(WRITE),
+   REQ_OP_NAME(FLUSH),
+   REQ_OP_NAME(DISCARD),
+   REQ_OP_NAME(SECURE_ERASE),
+   REQ_OP_NAME(ZONE_RESET),
+   REQ_OP_NAME(WRITE_SAME),
+   REQ_OP_NAME(WRITE_ZEROES),
+   REQ_OP_NAME(SCSI_IN),
+   REQ_OP_NAME(SCSI_OUT),
+   REQ_OP_NAME(DRV_IN),
+   REQ_OP_NAME(DRV_OUT),
+};
+#undef REQ_OP_NAME
+
+/**
+ * blk_op_str - Return string XXX in the REQ_OP_XXX.
+ * @op: REQ_OP_XXX.
+ *
+ * Description: Centralize block layer function to convert REQ_OP_XXX into
+ * string format. Useful in the debugging and tracing bio or request. For
+ * invalid REQ_OP_XXX it returns string "UNKNOWN".
+ */
+inline const char *blk_op_str(unsigned int op)
+{
+   const char *op_str = "UNKNOWN";
+
+   if (op < ARRAY_SIZE(blk_op_name) && blk_op_name[op])
+       op_str = blk_op_name[op];
+
+   return op_str;
+}
+EXPORT_SYMBOL_GPL(blk_op_str);
+
 static const struct {
    int     errno;
    const char  *name;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d5d3bb4..0c48237 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -865,6 +865,9 @@ extern void blk_execute_rq(struct request_queue *, struct gendisk *,
 extern void blk_execute_rq_nowait(struct request_queue *, struct gendisk *,
                  struct request *, int, rq_end_io_fn *);

+/* Helper to convert REQ_OP_XXX to its string format XXX */
+extern const char *blk_op_str(unsigned int op);
+
 int blk_status_to_errno(blk_status_t status);
 blk_status_t errno_to_blk_status(int errno);

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