Add disk usage detection based on access counters

HISTORY

@@ -6,7 +6,8 @@ SnapRAID HISTORY
  * Added detection of `smartctl` executable. Improves reliability when running
    under `sudo` or environments where `/sbin` and `/usr/sbin` are not in PATH.
  * Avoided saving the content file when it was not strictly necessary.
- * More log tags for the `status` command [Tristan Teufel]
+ * More log tags for the `status` command [Tristan Teufel].
+ * More log tags for the `probe` command.
  * Added documentation of the tags used in the log file in the new
    snapraid_log manpage.
  * Added manual translations in multiple languages.

cmdline/device.c

@@ -558,6 +558,8 @@ static void state_info_log(devinfo_t* devinfo)
 		log_tag("attr:%s:%s:size:%" PRIu64 "\n", devinfo->file, devinfo->name, devinfo->info[INFO_SIZE]);
 	if (devinfo->info[INFO_ROTATION_RATE] != SMART_UNASSIGNED)
 		log_tag("attr:%s:%s:rotationrate:%" PRIu64 "\n", devinfo->file, devinfo->name, devinfo->info[INFO_ROTATION_RATE]);
+	if (devinfo->access_stat != 0)
+		log_tag("attr:%s:%s:stat:%" PRIu64 "\n", devinfo->file, devinfo->name, devinfo->access_stat);
 }
 
 static void state_smart_log(devinfo_t* devinfo, double afr)

cmdline/portable.h

@@ -520,6 +520,7 @@ struct devinfo_struct {
 	struct devinfo_struct* parent; /**< Pointer at the parent if any. */
 	uint64_t smart[SMART_COUNT]; /**< SMART attributes. */
 	uint64_t info[INFO_COUNT]; /**< Info attributes. */
+	uint64_t access_stat; /**< Access stat. */
 	char serial[SMART_MAX]; /**< Serial number. */
 	char family[SMART_MAX]; /**< Family. */
 	char model[SMART_MAX]; /**< Model. */

cmdline/unix.c

@@ -1274,6 +1274,192 @@ static int devsmart(dev_t device, const char* name, const char* smartctl, uint64
 }
 #endif
 
+/**
+ * Compute disk usage by aggregating access statistics.
+ *
+ * This function determines whether a disk has been used by summing read
+ * and write access counters from all related partitions and device holders.
+ * Disk-level statistics are not used directly, as they may include
+ * kernel-generated fake accesses that do not reflect real I/O activity.
+ *
+ * By walking the device hierarchy and accumulating per-device statistics,
+ * the function provides a reliable measure of actual disk usage between
+ * sampling points.
+ */
+#if HAVE_LINUX_DEVICE
+static int devstat_recurse(dev_t device, uint64_t* count)
+{
+	char device_path[PATH_MAX];
+	char path[PATH_MAX];
+	char buf[512];
+	char* device_file;
+	int device_len;
+	DIR* d;
+	struct dirent* dd;
+	int holders = 0;
+	int partitions = 0;
+	int token;
+	int ret;
+	char* i;
+
+	/* get the device name */
+	if (devresolve(device, device_path, sizeof(device_path)) != 0)
+		return -1;
+
+	device_len = strlen(device_path);
+	if (device_len <= 5)
+		return -1;
+	device_file = device_path + 5; /* skip /dev/ */
+	device_len -= 5;
+
+	pathprint(path, sizeof(path), "/sys/dev/block/%u:%u", major(device), minor(device));
+
+	/* check if there are partitions */
+	d = opendir(path);
+	if (d == 0) 
+		return -1;
+
+	while ((dd = readdir(d)) != 0) {
+		dev_t subdev;
+
+		if (dd->d_name[0] == '.') 
+			continue;
+
+		if (strncmp(device_file, dd->d_name, device_len) != 0)
+			continue;
+
+		pathprint(path, sizeof(path), "/sys/dev/block/%u:%u/%s/dev", major(device), minor(device), dd->d_name);
+
+		subdev = devread(path);
+		if (!subdev) {
+			/* LCOV_EXCL_START */
+			closedir(d);
+			return -1;
+			/* LCOV_EXCL_STOP */
+		}
+
+		if (devstat_recurse(subdev, count) != 0) {
+			/* LCOV_EXCL_START */
+			closedir(d);
+			return -1;
+			/* LCOV_EXCL_STOP */
+		}
+		
+		++partitions;
+	}
+
+	closedir(d);
+
+	/* stop if processed partitions */
+	if (partitions != 0)
+		return 0;
+
+	pathprint(path, sizeof(path), "/sys/dev/block/%u:%u/holders", major(device), minor(device));
+
+	/* check if there are holders */
+	d = opendir(path);
+	if (d == 0) 
+		return -1;
+
+	while ((dd = readdir(d)) != 0) {
+		dev_t subdev;
+
+		if (dd->d_name[0] == '.') 
+			continue;
+				
+
+		/* for each slave, expand the full potential tree */
+		pathprint(path, sizeof(path), "/sys/dev/block/%u:%u/holders/%s/dev", major(device), minor(device), dd->d_name);
+
+		subdev = devread(path);
+		if (!subdev) {
+			/* LCOV_EXCL_START */
+			closedir(d);
+			return -1;
+			/* LCOV_EXCL_STOP */
+		}
+
+		if (devstat_recurse(subdev, count) != 0) {
+			/* LCOV_EXCL_START */
+			closedir(d);
+			return -1;
+			/* LCOV_EXCL_STOP */
+		}
+
+		++holders;
+	}
+
+	closedir(d);
+
+	/* stop if processed holders */
+	if (holders != 0)
+		return 0;
+
+	pathprint(path, sizeof(path), "/sys/dev/block/%u:%u/stat", major(device), minor(device));
+
+	ret = sysread(path, buf, sizeof(buf));
+	if (ret < 0) {
+		/* LCOV_EXCL_START */
+		log_fatal("Failed to read '%s'.\n", path);
+		return -1;
+		/* LCOV_EXCL_STOP */
+	}
+	if ((size_t)ret + 1 > sizeof(buf)) {
+		/* LCOV_EXCL_START */
+		log_fatal("Too long read '%s'.\n", path);
+		return -1;
+		/* LCOV_EXCL_STOP */
+	}
+
+	/* ending 0 */
+	buf[ret] = 0;
+
+	i = buf;
+	token = 1; /* token number */
+	while (*i) {
+		char* n;
+		char* e;
+		unsigned long long v;
+
+		/* skip spaces */
+		while (*i && isspace(*i))
+			++i;
+
+		/* read digits */
+		n = i;
+		while (*i && isdigit(*i))
+			++i;
+
+		if (i == n) /* if no digit, abort */
+			break;
+		if (*i == 0 || !isspace(*i)) /* if no space, abort */
+			break;
+		*i++ = 0; /* put a terminator */
+
+		v = strtoull(n, &e, 10);
+		if (*e != 0)
+			break;
+
+		/* sum reads and writes completed */
+		if (token == 1 || token == 5) {
+			*count += v;
+			if (token == 5)
+				break; /* stop here */
+		}
+
+		++token;
+	}
+
+	return 0;
+}
+
+static int devstat(dev_t device, uint64_t* count)
+{
+	*count = 0;
+	return devstat_recurse(device, count);
+}
+#endif
+
 /**
  * Get device attributes.
  */
@@ -1731,6 +1917,11 @@ static void* thread_probe(void* arg)
 	 */
 	devattr(devinfo->device, devinfo->info, devinfo->serial, devinfo->family, devinfo->model);
 
+	/*
+	 * Retrieve access stat for the device
+	 */
+	devstat(devinfo->device, &devinfo->access_stat);
+
 	return 0;
 #else
 	(void)arg;

doc/snapraid_log.1

@@ -1592,6 +1592,18 @@ read.
 .B attr:<device_file>:<disk_name>[/<split_index>]:power:down
 Logs a successful spin\-down operation initiated via the
 smartctl command.
+.TP
+.B attr:<device_file>:<disk_name>[/<split_index>]:stat:<access_number>
+Logs the total number of read and write accesses done on the disk.
+Comparing this number at different times, you can detect if the
+disk was used during that time.
+.RS 4
+.PD 0
+.HP 4
+.I <access_number>
+Total number of accesses (int64).
+.PD
+.RE
 .SS Summary 
 Tags logging the overall failure probabilities for the array.
 .TP

doc/snapraid_log.d

@@ -1016,6 +1016,13 @@ Command Smart Tags
 		Logs a successful spin-down operation initiated via the 
 		smartctl command.
 
+	=attr:<device_file>:<disk_name>[/<split_index>]:stat:<access_number>
+		Logs the total number of read and write accesses done on the disk.
+		Comparing this number at different times, you can detect if the
+		disk was used during that time.
+
+		<access_number> - Total number of accesses (int64).
+
     Summary
 	Tags logging the overall failure probabilities for the array.
 

doc/snapraid_log.txt

@@ -1058,6 +1058,13 @@ Tags logging specific disk identification and attribute values.
         Logs a successful spin-down operation initiated via the
         smartctl command.
 
+    attr:<device_file>:<disk_name>[/<split_index>]:stat:<access_number>
+        Logs the total number of read and write accesses done on the disk.
+        Comparing this number at different times, you can detect if the
+        disk was used during that time.
+
+    <access_number> - Total number of accesses (int64).
+
 ---- 14.0.2 Summary ----
 Tags logging the overall failure probabilities for the array.