[PATCH 4/5] btrfs: hook scrub session tracking into btrfs_scrub_dev()

[Torstein Eide <torsteine@gmail.com>]

From: Torstein Eide <torsteine@gmail.com>

At the start of a scrub (excluding device replace runs):
  - zero all per-device scrub_session_values[] counters
  - set scrub_session_last_physical to the start offset
  - record scrub_session_t_start (wall-clock seconds)
  - set scrub_session_status to BTRFS_SCRUB_STATUS_RUNNING

At the end of a scrub, call btrfs_update_scrub_stats() which copies
the final btrfs_scrub_progress counters into the session and lifetime
arrays, stamps t_end, and sets the status to FINISHED or CANCELED
depending on the return value.

Device replace runs are excluded because their progress is tracked
separately and their statistics should not pollute the device's own
scrub history.

Signed-off-by: Torstein Eide <torsteine@gmail.com>
Assisted-by: Claude:claude-sonnet-4-6
---
 fs/btrfs/scrub.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 1ac609239cbe3..a3bf3276f5f44 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -6,6 +6,7 @@
 #include <linux/blkdev.h>
 #include <linux/ratelimit.h>
 #include <linux/sched/mm.h>
+#include <linux/timekeeping.h>
 #include "ctree.h"
 #include "discard.h"
 #include "volumes.h"
@@ -3152,6 +3153,18 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
 	dev->scrub_ctx = sctx;
 	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
 
+	if (!is_dev_replace) {
+		int i;
+
+		/* Reset session counters for this new scrub run */
+		for (i = 0; i < BTRFS_SCRUB_STAT_VALUES_MAX; i++)
+			atomic64_set(&dev->scrub_session_values[i], 0);
+		dev->scrub_session_last_physical = start;
+		dev->scrub_session_t_start = ktime_get_real_seconds();
+		dev->scrub_session_t_end = 0;
+		atomic_set(&dev->scrub_session_status, BTRFS_SCRUB_STATUS_RUNNING);
+	}
+
 	/*
 	 * checking @scrub_pause_req here, we can avoid
 	 * race between committing transaction and scrubbing.
@@ -3207,6 +3220,9 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
 	if (progress)
 		memcpy(progress, &sctx->stat, sizeof(*progress));
 
+	if (!is_dev_replace)
+		btrfs_update_scrub_stats(dev, &sctx->stat, ret);
+
 	if (!is_dev_replace)
 		btrfs_info(fs_info, "scrub: %s on devid %llu with status: %d",
 			ret ? "not finished" : "finished", devid, ret);
-- 
2.48.1