[PATCH 2/5] btrfs: add in-memory scrub lifetime and session fields

[Torstein Eide <torsteine@gmail.com>]

From: Torstein Eide <torsteine@gmail.com>

Extend struct btrfs_device with two counter arrays and session metadata:

  scrub_stat_values[]    - lifetime totals, persisted across mounts via
                           the new BTRFS_SCRUB_STATS_OBJECTID tree item.
                           Protected by an atomic dirty counter
                           (scrub_stats_ccnt) and flushed at transaction
                           commit by btrfs_run_scrub_stats().

  scrub_session_values[] - per-run counters reset when a new scrub
                           starts; never written to disk.

  scrub_session_{t_start,t_end,last_physical,status} - timing and
                           progress metadata for the current or most
                           recent scrub session on this device.

Add matching kobject pointers (scrub_kobj, scrub_lifetime_kobj,
scrub_session_kobj) to both struct btrfs_device and struct btrfs_fs_info
for the sysfs hierarchy added in a later patch.

Add BTRFS_SCRUB_STATUS_* constants and the inline read/write helpers
btrfs_scrub_stat_{read,add,set}() and btrfs_scrub_session_read().
The add/set helpers include an smp_mb__before_atomic() to order stat
updates before the dirty-counter increment, pairing with the smp_rmb()
in btrfs_run_scrub_stats().

Signed-off-by: Torstein Eide <torsteine@gmail.com>
Assisted-by: Claude:claude-sonnet-4-6
---
 fs/btrfs/fs.h      |  5 +++
 fs/btrfs/volumes.h | 79 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+)

diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
index a4758d94b32e9..c333e30c93e40 100644
--- a/fs/btrfs/fs.h
+++ b/fs/btrfs/fs.h
@@ -714,6 +714,11 @@ struct btrfs_fs_info {
 	struct kobject *qgroups_kobj;
 	struct kobject *discard_kobj;
 
+	/* For /sys/fs/btrfs/<UUID>/scrub/{lifetime,session}/ */
+	struct kobject *scrub_kobj;
+	struct kobject *scrub_lifetime_kobj;
+	struct kobject *scrub_session_kobj;
+
 	/* Track the number of blocks (sectors) read by the filesystem. */
 	struct percpu_counter stats_read_blocks;
 
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 0082c166af91f..e77f726928abd 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -200,6 +200,29 @@ struct btrfs_device {
 	atomic_t dev_stats_ccnt;
 	atomic_t dev_stat_values[BTRFS_DEV_STAT_VALUES_MAX];
 
+	/*
+	 * Scrub lifetime counters. Persisted via BTRFS_SCRUB_STATS_OBJECTID
+	 * tree items in the device tree; loaded at mount by
+	 * btrfs_init_scrub_stats(), flushed at commit by btrfs_run_scrub_stats().
+	 * Index values defined by BTRFS_SCRUB_STAT_* in btrfs_tree.h.
+	 */
+	int scrub_stats_valid;
+	atomic_t scrub_stats_ccnt;
+	atomic64_t scrub_stat_values[BTRFS_SCRUB_STAT_VALUES_MAX];
+
+	/*
+	 * Per-session scrub counters. Reset to zero when a new scrub starts on
+	 * this device. Never persisted to disk.
+	 */
+	atomic64_t scrub_session_values[BTRFS_SCRUB_STAT_VALUES_MAX];
+	/* Resume offset at end of session */
+	u64 scrub_session_last_physical;
+	/* Unix time (seconds) when the session started / ended (0 if idle) */
+	u64 scrub_session_t_start;
+	u64 scrub_session_t_end;
+	/* BTRFS_SCRUB_STATUS_* */
+	atomic_t scrub_session_status;
+
 	/*
 	 * Device's major-minor number. Must be set even if the device is not
 	 * opened (bdev == NULL), unless the device is missing.
@@ -211,6 +234,10 @@ struct btrfs_device {
 	struct completion kobj_unregister;
 	/* For sysfs/FSID/devinfo/devid/ */
 	struct kobject devid_kobj;
+	/* For sysfs/FSID/devinfo/devid/scrub/ hierarchy */
+	struct kobject *scrub_kobj;
+	struct kobject *scrub_lifetime_kobj;
+	struct kobject *scrub_session_kobj;
 
 	/* Bandwidth limit for scrub, in bytes */
 	u64 scrub_speed_max;
@@ -864,6 +891,58 @@ static inline void btrfs_dev_stat_set(struct btrfs_device *dev,
 	atomic_inc(&dev->dev_stats_ccnt);
 }
 
+/*
+ * Scrub session status values stored in device->scrub_session_status.
+ */
+#define BTRFS_SCRUB_STATUS_IDLE		0
+#define BTRFS_SCRUB_STATUS_RUNNING	1
+#define BTRFS_SCRUB_STATUS_FINISHED	2
+#define BTRFS_SCRUB_STATUS_CANCELED	3
+
+static inline u64 btrfs_scrub_stat_read(const struct btrfs_device *dev,
+					int index)
+{
+	return (u64)atomic64_read(&dev->scrub_stat_values[index]);
+}
+
+static inline void btrfs_scrub_stat_add(struct btrfs_device *dev,
+					int index, u64 val)
+{
+	atomic64_add((long long)val, &dev->scrub_stat_values[index]);
+	/*
+	 * Order the stat update before the dirty-counter increment so that
+	 * btrfs_run_scrub_stats() observes a consistent snapshot.  Pairs with
+	 * smp_rmb() in btrfs_run_scrub_stats().
+	 */
+	smp_mb__before_atomic();
+	atomic_inc(&dev->scrub_stats_ccnt);
+}
+
+static inline void btrfs_scrub_stat_set(struct btrfs_device *dev,
+					int index, u64 val)
+{
+	atomic64_set(&dev->scrub_stat_values[index], (long long)val);
+	/*
+	 * Order the stat update before the dirty-counter increment so that
+	 * btrfs_run_scrub_stats() observes a consistent snapshot.  Pairs with
+	 * smp_rmb() in btrfs_run_scrub_stats().
+	 */
+	smp_mb__before_atomic();
+	atomic_inc(&dev->scrub_stats_ccnt);
+}
+
+static inline u64 btrfs_scrub_session_read(const struct btrfs_device *dev,
+					   int index)
+{
+	return (u64)atomic64_read(&dev->scrub_session_values[index]);
+}
+
+int btrfs_init_scrub_stats(struct btrfs_fs_info *fs_info);
+int btrfs_run_scrub_stats(struct btrfs_trans_handle *trans);
+void btrfs_update_scrub_stats(struct btrfs_device *dev,
+			      const struct btrfs_scrub_progress *progress,
+			      int scrub_ret);
+
 static inline const char *btrfs_dev_name(const struct btrfs_device *device)
 {
 	if (!device || test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
-- 
2.48.1