linux-kernel - [PATCH linux next] taskstats: fix struct taskstats breaks backward compatibility since version 15

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Message-ID: <20250510155413259V4JNRXxukdDgzsaL0Fo6a@zte.com.cn>
Date: Sat, 10 May 2025 15:54:13 +0800 (CST)
From: <jiang.kun2@....com.cn>
To: <bbonev@...uan.org>, <linux-kernel@...r.kernel.org>
Cc: <bsingharora@...il.com>, <yang.yang29@....com.cn>, <wang.yaxin@....com.cn>,
        <jiang.kun2@....com.cn>, <xu.xin16@....com.cn>,
        <akpm@...ux-foundation.org>
Subject: [PATCH linux next] taskstats: fix struct taskstats breaks backward
 compatibility since version 15

From: Wang Yaxin <wang.yaxin@....com.cn>

Problem
========
commit 658eb5ab916d ("delayacct: add delay max to record
 delay peak") - adding more fields
commit f65c64f311ee ("delayacct: add delay min to record
 delay peak") - adding more fields
commit b016d0873777 ("taskstats: modify taskstats version")
 - version bump to 15

Since version 15 (TASKSTATS_VERSION=15) the new layout of the
structure adds fields in the middle of the structure, rendering
all old software incompatible with newer kernels and software
compiled against the new kernel headers incompatible with older
kernels.

Solution
=========
move delay max and delay min to the end of taskstat, and bump
the version to 16 after the change

Signed-off-by: Wang Yaxin <wang.yaxin@....com.cn>
Signed-off-by: xu xin <xu.xin16@....com.cn>
Signed-off-by: Kun Jiang <jiang.kun2@....com.cn>
---
 include/uapi/linux/taskstats.h | 43 +++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 16 deletions(-)
diff --git a/include/uapi/linux/taskstats.h b/include/uapi/linux/taskstats.h
index 95762232e018..d71aa022b2ef 100644
--- a/include/uapi/linux/taskstats.h
+++ b/include/uapi/linux/taskstats.h
@@ -34,7 +34,7 @@
  */


-#define TASKSTATS_VERSION	15
+#define TASKSTATS_VERSION	16
 #define TS_COMM_LEN		32	/* should be >= TASK_COMM_LEN
 					 * in linux/sched.h */

@@ -72,8 +72,6 @@ struct taskstats {
 	 */
 	__u64	cpu_count __attribute__((aligned(8)));
 	__u64	cpu_delay_total;
-	__u64	cpu_delay_max;
-	__u64	cpu_delay_min;

 	/* Following four fields atomically updated using task->delays->lock */

@@ -82,14 +80,10 @@ struct taskstats {
 	 */
 	__u64	blkio_count;
 	__u64	blkio_delay_total;
-	__u64	blkio_delay_max;
-	__u64	blkio_delay_min;

 	/* Delay waiting for page fault I/O (swap in only) */
 	__u64	swapin_count;
 	__u64	swapin_delay_total;
-	__u64	swapin_delay_max;
-	__u64	swapin_delay_min;

 	/* cpu "wall-clock" running time
 	 * On some architectures, value will adjust for cpu time stolen
@@ -172,14 +166,11 @@ struct taskstats {
 	/* Delay waiting for memory reclaim */
 	__u64	freepages_count;
 	__u64	freepages_delay_total;
-	__u64	freepages_delay_max;
-	__u64	freepages_delay_min;
+

 	/* Delay waiting for thrashing page */
 	__u64	thrashing_count;
 	__u64	thrashing_delay_total;
-	__u64	thrashing_delay_max;
-	__u64	thrashing_delay_min;

 	/* v10: 64-bit btime to avoid overflow */
 	__u64	ac_btime64;		/* 64-bit begin time */
@@ -187,8 +178,6 @@ struct taskstats {
 	/* v11: Delay waiting for memory compact */
 	__u64	compact_count;
 	__u64	compact_delay_total;
-	__u64	compact_delay_max;
-	__u64	compact_delay_min;

 	/* v12 begin */
 	__u32   ac_tgid;	/* thread group ID */
@@ -210,15 +199,37 @@ struct taskstats {
 	/* v13: Delay waiting for write-protect copy */
 	__u64    wpcopy_count;
 	__u64    wpcopy_delay_total;
-	__u64    wpcopy_delay_max;
-	__u64    wpcopy_delay_min;

 	/* v14: Delay waiting for IRQ/SOFTIRQ */
 	__u64    irq_count;
 	__u64    irq_delay_total;
+
+	/* v15: add Delay max and Delay min */
+
+	/* v16: move Delay max and Delay min to the end of taskstat */
+	__u64	cpu_delay_max;
+	__u64	cpu_delay_min;
+
+	__u64	blkio_delay_max;
+	__u64	blkio_delay_min;
+
+	__u64	swapin_delay_max;
+	__u64	swapin_delay_min;
+
+	__u64	freepages_delay_max;
+	__u64	freepages_delay_min;
+
+	__u64	thrashing_delay_max;
+	__u64	thrashing_delay_min;
+
+	__u64	compact_delay_max;
+	__u64	compact_delay_min;
+
+	__u64    wpcopy_delay_max;
+	__u64    wpcopy_delay_min;
+
 	__u64    irq_delay_max;
 	__u64    irq_delay_min;
-	/* v15: add Delay max */
 };


-- 
2.25.1