linux-kernel - [PATCH blktrace v3 12/20] blkiomon: read 'magic' first

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Message-ID: <20251015105658.527262-13-johannes.thumshirn@wdc.com>
Date: Wed, 15 Oct 2025 12:56:50 +0200
From: Johannes Thumshirn <johannes.thumshirn@....com>
To: axboe@...nel.dk
Cc: chaitanyak@...dia.com,
	dlemoal@...nel.org,
	hare@...e.de,
	hch@....de,
	john.g.garry@...cle.com,
	linux-block@...r.kernel.org,
	linux-btrace@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	martin.petersen@...cle.com,
	mathieu.desnoyers@...icios.com,
	mhiramat@...nel.org,
	naohiro.aota@....com,
	rostedt@...dmis.org,
	shinichiro.kawasaki@....com,
	Johannes Thumshirn <johannes.thumshirn@....com>
Subject: [PATCH blktrace v3 12/20] blkiomon: read 'magic' first

Similar to blkparse, read the 'magic' portion of 'struct blk_io_trace'
first when reading the trace.

This is a preparation of supporting multiple trace protocol versions.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
---
 blkiomon.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/blkiomon.c b/blkiomon.c
index f8b0c9d..05f2d00 100644
--- a/blkiomon.c
+++ b/blkiomon.c
@@ -460,19 +460,28 @@ static int blkiomon_do_fifo(void)
 	bit = &t->bit;
 
 	while (up) {
+		__u32 magic;
+
+		if (fread(&magic, sizeof(magic), 1, ifp) != 1) {
+			if (!feof(ifp))
+				fprintf(stderr,
+					"blkiomon: could not read trace");
+			break;
+		}
 		if (fread(bit, sizeof(*bit), 1, ifp) != 1) {
 			if (!feof(ifp))
 				fprintf(stderr,
 					"blkiomon: could not read trace");
 			break;
 		}
+		bit->magic = magic;
 		if (ferror(ifp)) {
 			clearerr(ifp);
 			fprintf(stderr, "blkiomon: error while reading trace");
 			break;
 		}
 
-		if (data_is_native == -1 && check_data_endianness(bit->magic)) {
+		if (data_is_native == -1 && check_data_endianness(magic)) {
 			fprintf(stderr, "blkiomon: endianess problem\n");
 			break;
 		}
-- 
2.51.0