[PATCH] Aggregated disk statistics

From: Rick Lindsley <ricklind@us.ibm.com>

To access all the system's disk statitics we currently need to access one
sysfs file per disk.  This clearly will not be acceptable with thousands of
disks.

The patch aggregates the system-wide statistics in real time and exposes them
via /proc/diskstats

drivers/block/genhd.c

@@ -544,6 +544,92 @@ static struct kset_hotplug_ops block_hotplug_ops = {
 static decl_subsys(block, &ktype_block, &block_hotplug_ops);
 
 
+/*
+ * aggregate disk stat collector.  Uses the same stats that the sysfs
+ * entries do, above, but makes them available through one seq_file.
+ * Watching a few disks may be efficient through sysfs, but watching
+ * all of them will be more efficient through this interface.
+ *
+ * The output looks suspiciously like /proc/partitions with a bunch of
+ * extra fields.
+ */
+
+/* iterator */
+static void *diskstats_start(struct seq_file *part, loff_t *pos)
+{
+	loff_t k = *pos;
+	struct list_head *p;
+
+	down_read(&block_subsys.rwsem);
+	list_for_each(p, &block_subsys.kset.list)
+		if (!k--)
+			return list_entry(p, struct gendisk, kobj.entry);
+	return NULL;
+}
+
+static void *diskstats_next(struct seq_file *part, void *v, loff_t *pos)
+{
+	struct list_head *p = ((struct gendisk *)v)->kobj.entry.next;
+	++*pos;
+	return p==&block_subsys.kset.list ? NULL :
+		list_entry(p, struct gendisk, kobj.entry);
+}
+
+static void diskstats_stop(struct seq_file *part, void *v)
+{
+	up_read(&block_subsys.rwsem);
+}
+
+static int diskstats_show(struct seq_file *s, void *v)
+{
+	struct gendisk *gp = v;
+	char buf[64];
+	int n = 0;
+
+	/*
+	if (&sgp->kobj.entry == block_subsys.kset.list.next)
+		seq_puts(s,	"major minor name"
+				"     rio rmerge rsect ruse wio wmerge "
+				"wsect wuse running use aveq"
+				"\n\n");
+	*/
+ 
+	disk_round_stats(gp);
+	seq_printf(s, "%4d %4d %s %u %u %llu %u %u %u %llu %u %u %u %u\n",
+		gp->major, n + gp->first_minor, disk_name(gp, n, buf),
+		disk_stat_read(gp, reads), disk_stat_read(gp, read_merges),
+		(unsigned long long)disk_stat_read(gp, read_sectors),
+		jiffies_to_msec(disk_stat_read(gp, read_ticks)),
+		disk_stat_read(gp, writes), disk_stat_read(gp, write_merges),
+		(unsigned long long)disk_stat_read(gp, write_sectors),
+		jiffies_to_msec(disk_stat_read(gp, write_ticks)),
+		disk_stat_read(gp, in_flight),
+		jiffies_to_msec(disk_stat_read(gp, io_ticks)),
+		jiffies_to_msec(disk_stat_read(gp, time_in_queue)));
+
+	/* now show all non-0 size partitions of it */
+	for (n = 0; n < gp->minors - 1; n++) {
+		struct hd_struct *hd = gp->part[n];
+
+		if (hd && hd->nr_sects)
+			seq_printf(s, "%4d %4d %s %u %u %u %u\n",
+				gp->major, n + gp->first_minor + 1,
+				disk_name(gp, n + 1, buf),
+				hd->reads, hd->read_sectors,
+				hd->writes, hd->write_sectors);
+	}
+ 
+	return 0;
+}
+
+struct seq_operations diskstats_op = {
+	start:	diskstats_start,
+	next:	diskstats_next,
+	stop:	diskstats_stop,
+	show:	diskstats_show
+};
+
+
 struct gendisk *alloc_disk(int minors)
 {
 	struct gendisk *disk = kmalloc(sizeof(struct gendisk), GFP_KERNEL);

fs/proc/proc_misc.c

@@ -333,6 +333,18 @@ static struct file_operations proc_partitions_operations = {
 	.release	= seq_release,
 };
 
+extern struct seq_operations diskstats_op;
+static int diskstats_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &diskstats_op);
+}
+static struct file_operations proc_diskstats_operations = {
+	open:		diskstats_open,
+	read:		seq_read,
+	llseek:		seq_lseek,
+	release:	seq_release,
+};
+
 #ifdef CONFIG_MODULES
 extern struct seq_operations modules_op;
 static int modules_open(struct inode *inode, struct file *file)
@@ -644,6 +656,7 @@ void __init proc_misc_init(void)
 	create_seq_entry("slabinfo",S_IWUSR|S_IRUGO,&proc_slabinfo_operations);
 	create_seq_entry("buddyinfo",S_IRUGO, &fragmentation_file_operations);
 	create_seq_entry("vmstat",S_IRUGO, &proc_vmstat_file_operations);
+	create_seq_entry("diskstats", 0, &proc_diskstats_operations);
 #ifdef CONFIG_MODULES
 	create_seq_entry("modules", 0, &proc_modules_operations);
 #endif