[PATCH 1/1] blktrace: add support for REQ_OP_WRITE_ZEROES tracing

[Chaitanya Kulkarni <ckulkarnilinux@gmail.com>]

Currently, REQ_OP_WRITE_ZEROES operations are not handled in the 
blktrace infrastructure, resulting in incorrect or missing operation
labels in ftrace blktrace output. This manifests as write-zeroes
operations appearing with incorrect labels like "N" instead of a
proper "WZ" designation.

This patch adds complete support for REQ_OP_WRITE_ZEROES across the
blktrace infrastructure:

Add BLK_TC_WRITE_ZEROES trace category in blktrace_api.h and update
BLK_TC_END_V2 marker accordingly
Map REQ_OP_WRITE_ZEROES to BLK_TC_WRITE_ZEROES in __blk_add_trace()
to ensure proper trace event categorization
Update fill_rwbs() to generate "WZ" label for write-zeroes operations
in ftrace output, making them easily identifiable
Add "write-zeroes" string mapping in act_to_str array for debugfs
filter interface
Update blk_fill_rwbs() to handle REQ_OP_WRITE_ZEROES for block layer
event tracing

With this fix, write-zeroes operations are now correctly traced and
displayed.

===========================================================
BEFORE THIS PATCH
===========================================================
blkdiscard -z -o 0 -l 40960 /dev/nvme0n1
   blkdiscard-3809 [030] .....  1212.253701: block_bio_queue: 259,0 NS 0 + 80 [blkdiscard]
   blkdiscard-3809 [030] .....  1212.253703: block_getrq: 259,0 NS 0 + 80 [blkdiscard]
   blkdiscard-3809 [030] .....  1212.253704: block_io_start: 259,0 NS 40960 () 0 + 80 be,0,4 [blkdiscard]
   blkdiscard-3809 [030] .....  1212.253704: block_plug: [blkdiscard]
   blkdiscard-3809 [030] .....  1212.253706: block_unplug: [blkdiscard] 1
   blkdiscard-3809 [030] .....  1212.253706: block_rq_insert: 259,0 NS 40960 () 0 + 80 be,0,4 [blkdiscard]
kworker/30:1H-566  [030] .....  1212.253726: block_rq_issue: 259,0 NS 40960 () 0 + 80 be,0,4 [kworker/30:1H]
       <idle>-0    [030] d.h1.  1212.253957: block_rq_complete: 259,0 NS () 0 + 80 be,0,4 [0]
       <idle>-0    [030] dNh1.  1212.253960: block_io_done: 259,0 NS 0 () 0 + 0 none,0,0 [swapper/30]

Trace Event Breakdown:
 Event             | Device | Op  | Sector | Sectors | Byte Size | Calculation          

 block_bio_queue   | 259,0  | NS  | 0      | 80      | -         | 80 × 512 = 40,960    
 block_getrq       | 259,0  | NS  | 0      | 80      | -         | 80 × 512 = 40,960    
 block_io_start    | 259,0  | NS  | 0      | 80      | 40960     | Direct from trace  
 block_rq_insert   | 259,0  | NS  | 0      | 80      | 40960     | Direct from trace  
 block_rq_issue    | 259,0  | NS  | 0      | 80      | 40960     | Direct from trace  
 block_rq_complete | 259,0  | NS  | 0      | 80      | -         | 80 × 512 = 40,960    
 block_io_done     | 259,0  | NS  | 0      | 0       | 0         | Completion (no data) 

  Total Bytes Transferred: Sectors: 80 Bytes: 80 × 512 = 40,960 bytes

===========================================================
AFTER THIS PATCH
===========================================================
blkdiscard -z -o 0 -l 40960 /dev/nvme0n1

   blkdiscard-2477 [020] .....   960.989131: block_bio_queue: 259,0 WZS 0 + 80 [blkdiscard]
   blkdiscard-2477 [020] .....   960.989134: block_getrq: 259,0 WZS 0 + 80 [blkdiscard]
   blkdiscard-2477 [020] .....   960.989135: block_io_start: 259,0 WZS 40960 () 0 + 80 be,0,4 [blkdiscard]
   blkdiscard-2477 [020] .....   960.989138: block_plug: [blkdiscard]
   blkdiscard-2477 [020] .....   960.989140: block_unplug: [blkdiscard] 1
   blkdiscard-2477 [020] .....   960.989141: block_rq_insert: 259,0 WZS 40960 () 0 + 80 be,0,4 [blkdiscard]
kworker/20:1H-736  [020] .....   960.989166: block_rq_issue: 259,0 WZS 40960 () 0 + 80 be,0,4 [kworker/20:1H]
       <idle>-0    [020] d.h1.   960.989476: block_rq_complete: 259,0 WZS () 0 + 80 be,0,4 [0]
       <idle>-0    [020] dNh1.   960.989482: block_io_done: 259,0 WZS 0 () 0 + 0 none,0,0 [swapper/20]

Trace Event Breakdown:
 Event             | Device | Op  | Sector | Sectors | Byte Size | Calculation          

 block_bio_queue   | 259,0  | WZS | 0      | 80      | -         | 80 × 512 = 40,960    
 block_getrq       | 259,0  | WZS | 0      | 80      | -         | 80 × 512 = 40,960    
 block_io_start    | 259,0  | WZS | 0      | 80      | 40960     | Direct from trace  
 block_rq_insert   | 259,0  | WZS | 0      | 80      | 40960     | Direct from trace  
 block_rq_issue    | 259,0  | WZS | 0      | 80      | 40960     | Direct from trace  
 block_rq_complete | 259,0  | WZS | 0      | 80      | -         | 80 × 512 = 40,960    
 block_io_done     | 259,0  | WZS | 0      | 0       | 0         | Completion (no data) 

  Total Bytes Transferred: Sectors: 80 Bytes: 80 × 512 = 40,960 bytes

Tested with ftrace blktrace on NVMe devices using blkdiscard with
the -z (write-zeroes) flag.

Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
---
 include/uapi/linux/blktrace_api.h |  4 +++-
 kernel/trace/blktrace.c           | 13 ++++++++++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/blktrace_api.h b/include/uapi/linux/blktrace_api.h
index 30f3d2589365..7c092d9f3aa4 100644
--- a/include/uapi/linux/blktrace_api.h
+++ b/include/uapi/linux/blktrace_api.h
@@ -35,7 +35,9 @@ enum blktrace_cat {
 	BLK_TC_ZONE_OPEN	= 1ull << 20,	/* zone open */
 	BLK_TC_ZONE_CLOSE	= 1ull << 21,	/* zone close */
 
-	BLK_TC_END_V2		= 1ull << 21,
+	BLK_TC_WRITE_ZEROES	= 1ull << 22,	/* write-zeroes */
+
+	BLK_TC_END_V2		= 1ull << 22,
 };
 
 #define BLK_TC_SHIFT		(16)
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 4a37d9aa0481..1dd3b6a71649 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -360,6 +360,9 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	case REQ_OP_ZONE_CLOSE:
 		what |= BLK_TC_ACT(BLK_TC_ZONE_CLOSE);
 		break;
+	case REQ_OP_WRITE_ZEROES:
+		what |= BLK_TC_ACT(BLK_TC_WRITE_ZEROES);
+		break;
 	default:
 		break;
 	}
@@ -1414,7 +1417,10 @@ static void fill_rwbs(char *rwbs, const struct blk_io_trace2 *t)
 
 	if (tc & BLK_TC_DISCARD)
 		rwbs[i++] = 'D';
-	else if (tc & BLK_TC_WRITE)
+	else if (tc & BLK_TC_WRITE_ZEROES) {
+		rwbs[i++] = 'W';
+		rwbs[i++] = 'Z';
+	} else if (tc & BLK_TC_WRITE)
 		rwbs[i++] = 'W';
 	else if (t->bytes)
 		rwbs[i++] = 'R';
@@ -1957,6 +1963,7 @@ static const struct {
 	{ BLK_TC_DISCARD,	"discard"	},
 	{ BLK_TC_DRV_DATA,	"drv_data"	},
 	{ BLK_TC_FUA,		"fua"		},
+	{ BLK_TC_WRITE_ZEROES,	"write-zeroes"	},
 };
 
 static int blk_trace_str2mask(const char *str)
@@ -2170,6 +2177,10 @@ void blk_fill_rwbs(char *rwbs, blk_opf_t opf)
 		rwbs[i++] = 'Z';
 		rwbs[i++] = 'C';
 		break;
+	case REQ_OP_WRITE_ZEROES:
+		rwbs[i++] = 'W';
+		rwbs[i++] = 'Z';
+		break;
 	default:
 		rwbs[i++] = 'N';
 	}
-- 
2.40.0