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Date:	Thu, 23 Oct 2008 19:12:09 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu, rjw@...k.pl,
	dipankar@...ibm.com, tglx@...uxtronix.de, andi@...stfloor.org
Subject: Re: [PATCH] v3 rudimentary tracing for Classic RCU


trivial ported it to seq_file.
seq_file are very good for the output buffer.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/kernel/rcuclassic_trace.c b/kernel/rcuclassic_trace.c
index d19780b..f19217c
--- a/kernel/rcuclassic_trace.c
+++ b/kernel/rcuclassic_trace.c
@@ -23,157 +23,167 @@
  * 		Documentation/RCU
  *
  */
-#include <linux/types.h>
-#include <linux/kernel.h>
-#include <linux/init.h>
-#include <linux/spinlock.h>
-#include <linux/smp.h>
 #include <linux/rcupdate.h>
-#include <linux/interrupt.h>
-#include <linux/sched.h>
-#include <asm/atomic.h>
-#include <linux/bitops.h>
 #include <linux/module.h>
-#include <linux/completion.h>
-#include <linux/moduleparam.h>
-#include <linux/percpu.h>
-#include <linux/notifier.h>
-#include <linux/cpu.h>
-#include <linux/mutex.h>
 #include <linux/debugfs.h>
+#include <linux/seq_file.h>
 
-static DEFINE_MUTEX(rcuclassic_trace_mutex);
-static char *rcuclassic_trace_buf;
-#define RCUCLASSIC_TRACE_BUF_SIZE (128 * num_possible_cpus() + 100)
+static struct rcu_data *get_rcu_data_bh(int cpu)
+{
+	return &per_cpu(rcu_bh_data, cpu);
+}
 
-static int print_one_rcu_data(struct rcu_data *rdp, char *buf, char *ebuf)
+static struct rcu_data *get_rcu_data(int cpu)
 {
-	int cnt = 0;
+	return &per_cpu(rcu_data, cpu);
+}
 
+static int show_rcu_data(struct seq_file *m, void *v)
+{
+	struct rcu_data *rdp = v;
 	if (!rdp->beenonline)
 		return 0;
-	cnt += snprintf(&buf[cnt], ebuf - &buf[cnt],
-		"%3d%cqb=%ld b=%ld pq=%d qsp=%d ql=%ld bl=%ld\n",
-		rdp->cpu, cpu_is_offline(rdp->cpu) ? '!' : ' ',
-		rdp->quiescbatch, rdp->batch, rdp->passed_quiesc,
-		rdp->qs_pending, rdp->qlen, rdp->blimit);
-	return cnt;
+
+	seq_printf(m, "processor\t: %d", rdp->cpu);
+	if (cpu_is_offline(rdp->cpu))
+		seq_puts(m, "!\n");
+	else
+		seq_puts(m, "\n");
+	seq_printf(m, "quiescbatch\t: %ld\n", rdp->quiescbatch);
+	seq_printf(m, "batch\t: %ld\n", rdp->batch);
+	seq_printf(m, "passed_quiesc\t: %d\n", rdp->passed_quiesc);
+	seq_printf(m, "qs_pending\t: %d\n", rdp->qs_pending);
+	seq_printf(m, "qlen\t: %ld\n", rdp->qlen);
+	seq_printf(m, "blimit\t: %ld\n", rdp->blimit);
+	seq_puts(m, "\n\n");
+	return 0;
 }
 
-#define PRINT_RCU_DATA(name, buf, ebuf) \
-	do { \
-		int _p_r_d_i; \
-		\
-		for_each_possible_cpu(_p_r_d_i) \
-			(buf) += print_one_rcu_data(&per_cpu(name, _p_r_d_i), \
-						    buf, ebuf); \
-	} while (0)
-
-static ssize_t rcudata_read(struct file *filp, char __user *buffer,
-				size_t count, loff_t *ppos)
+static void *c_start(struct seq_file *m, loff_t *pos)
 {
-	ssize_t bcount;
-	char *buf = rcuclassic_trace_buf;
-	char *ebuf = &rcuclassic_trace_buf[RCUCLASSIC_TRACE_BUF_SIZE];
-
-	mutex_lock(&rcuclassic_trace_mutex);
-	buf += snprintf(buf, ebuf - buf, "rcu:\n");
-	PRINT_RCU_DATA(rcu_data, buf, ebuf);
-	buf += snprintf(buf, ebuf - buf, "rcu_bh:\n");
-	PRINT_RCU_DATA(rcu_bh_data, buf, ebuf);
-	bcount = simple_read_from_buffer(buffer, count, ppos,
-			rcuclassic_trace_buf, strlen(rcuclassic_trace_buf));
-	mutex_unlock(&rcuclassic_trace_mutex);
-	return bcount;
+	typedef struct rcu_data *(*get_data_func)(int);
+
+	if (*pos == 0)	/* just in case, cpu 0 is not the first */
+		*pos = first_cpu(cpu_possible_map);
+	else
+		*pos = next_cpu_nr(*pos - 1, cpu_possible_map);
+	if ((*pos) < nr_cpu_ids)
+		return ((get_data_func)m->private)(*pos);
+	return NULL;
 }
 
-static int print_one_rcu_ctrlblk(struct rcu_ctrlblk *rcp, char *buf, char *ebuf)
+static void *c_next(struct seq_file *m, void *v, loff_t *pos)
 {
-	int cnt = 0;
-
-	cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], "cur=%ld  completed=%ld  "
-			"pending=%ld  s=%d\n\t",
-			rcp->cur, rcp->completed,
-			rcp->pending, rcp->signaled);
-	cnt += cpulist_scnprintf(&buf[cnt], ebuf - &buf[cnt], rcp->cpumask);
-	cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], "\n");
-	return cnt;
+	(*pos)++;
+	return c_start(m, pos);
 }
 
-static ssize_t rcucb_read(struct file *filp, char __user *buffer,
-				size_t count, loff_t *ppos)
+static void c_stop(struct seq_file *m, void *v)
 {
-	ssize_t bcount;
-	char *buf = rcuclassic_trace_buf;
-	char *ebuf = &rcuclassic_trace_buf[RCUCLASSIC_TRACE_BUF_SIZE];
-
-	mutex_lock(&rcuclassic_trace_mutex);
-	buf += snprintf(buf, ebuf - buf, "rcu: ");
-	buf += print_one_rcu_ctrlblk(&rcu_ctrlblk, buf, ebuf);
-	buf += snprintf(buf, ebuf - buf, "rcu_bh: ");
-	buf += print_one_rcu_ctrlblk(&rcu_bh_ctrlblk, buf, ebuf);
-	buf += snprintf(buf, ebuf - buf, "online: ");
-	buf += cpulist_scnprintf(buf, ebuf - buf, cpu_online_map);
-	buf += snprintf(buf, ebuf - buf, "\n");
-	bcount = simple_read_from_buffer(buffer, count, ppos,
-			rcuclassic_trace_buf, strlen(rcuclassic_trace_buf));
-	mutex_unlock(&rcuclassic_trace_mutex);
-	return bcount;
 }
 
-static struct file_operations rcudata_fops = {
-	.owner = THIS_MODULE,
-	.read = rcudata_read,
+const struct seq_operations rcu_data_seq_op = {
+	.start	= c_start,
+	.next	= c_next,
+	.stop	= c_stop,
+	.show	= show_rcu_data,
 };
 
+static int rcu_data_open(struct inode *inode, struct file *file)
+{
+	int ret = seq_open(file, &rcu_data_seq_op);
+	if (ret)
+		return ret;
+	((struct seq_file *)file->private_data)->private = inode->i_private;
+	return 0;
+}
+
+static const struct file_operations rcu_data_fops = {
+	.owner		= THIS_MODULE,
+	.open		= rcu_data_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static void print_one_rcu_ctrlblk(struct seq_file *m, struct rcu_ctrlblk *rcp)
+{
+	seq_printf(m, "cur=%ld  completed=%ld   pending=%ld  s=%d\n\t",
+			rcp->cur, rcp->completed, rcp->pending, rcp->signaled);
+	seq_cpumask(m, &rcp->cpumask);
+	seq_puts(m, "\n");
+}
+
+static int show_rcucb(struct seq_file *m, void *unused)
+{
+	seq_puts(m, "rcu: ");
+	print_one_rcu_ctrlblk(m, &rcu_ctrlblk);
+	seq_puts(m, "rcu_bh: ");
+	print_one_rcu_ctrlblk(m, &rcu_bh_ctrlblk);
+	seq_puts(m, "online: ");
+	seq_cpumask(m, &cpu_online_map);
+	seq_puts(m, "\n");
+	return 0;
+}
+
+static int rcucb_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, show_rcucb, NULL);
+}
+
 static struct file_operations rcucb_fops = {
-	.owner = THIS_MODULE,
-	.read = rcucb_read,
+	.owner		= THIS_MODULE,
+	.open		= rcucb_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
 };
 
-static struct dentry *rcudir, *datadir, *cbdir;
-static int rcuclassic_debugfs_init(void)
+static struct dentry *rcudir, *rcu_bh_data_file, *rcu_data_file, *rcucb_file;
+
+static int __init rcuclassic_trace_init(void)
 {
 	rcudir = debugfs_create_dir("rcu", NULL);
 	if (!rcudir)
 		goto out;
-	datadir = debugfs_create_file("rcudata", 0444, rcudir,
-				      NULL, &rcudata_fops);
-	if (!datadir)
-		goto free_out;
-	cbdir = debugfs_create_file("rcucb", 0444, rcudir, NULL, &rcucb_fops);
-	if (!cbdir)
-		goto free_out;
+
+	rcu_bh_data_file = debugfs_create_file("rcu_bh_data", 0444, rcudir,
+			get_rcu_data_bh, &rcu_data_fops);
+	if (!rcu_bh_data_file)
+		goto out_rcudir;
+
+	rcu_data_file = debugfs_create_file("rcu_data", 0444, rcudir,
+			get_rcu_data, &rcu_data_fops);
+	if (!rcu_data_file)
+		goto out_rcudata_bh_file;
+
+	rcucb_file = debugfs_create_file("rcucb", 0444, rcudir,
+			NULL, &rcucb_fops);
+	if (!rcucb_file)
+		goto out_rcudata_file;
 	return 0;
-free_out:
-	if (datadir)
-		debugfs_remove(datadir);
+
+out_rcudata_file:
+	debugfs_remove(rcu_data_file);
+out_rcudata_bh_file:
+	debugfs_remove(rcu_bh_data_file);
+out_rcudir:
 	debugfs_remove(rcudir);
 out:
 	return 1;
 }
 
-static int __init rcuclassic_trace_init(void)
-{
-	int ret;
-
-	rcuclassic_trace_buf = kmalloc(RCUCLASSIC_TRACE_BUF_SIZE, GFP_KERNEL);
-	if (!rcuclassic_trace_buf)
-		return 1;
-	ret = rcuclassic_debugfs_init();
-	if (ret)
-		kfree(rcuclassic_trace_buf);
-	return ret;
-}
-
 static void __exit rcuclassic_trace_cleanup(void)
 {
-	debugfs_remove(datadir);
-	debugfs_remove(cbdir);
+	debugfs_remove(rcucb_file);
+	debugfs_remove(rcu_data_file);
+	debugfs_remove(rcu_bh_data_file);
 	debugfs_remove(rcudir);
-	kfree(rcuclassic_trace_buf);
 }
 
-
 module_init(rcuclassic_trace_init);
 module_exit(rcuclassic_trace_cleanup);
+
+MODULE_AUTHOR("Paul E. McKenney");
+MODULE_DESCRIPTION("Read-Copy Update tracing for classic implementation");
+MODULE_LICENSE("GPL");

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