[PATCH] rcu: convert rcupreempt trace to seq file

[Li Zefan <lizf@cn.fujitsu.com>]

Impact: also fix a bug in show_rcustats()

Use seq file for simplification, and the global buffer and mutex can be
removed.

While doing this, I found rcustats will never show 'ggp' and 'rcc' fields
due to a bug in show_rcustats().

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/rcupreempt_trace.c |  155 ++++++++++++++++++++-------------------------
 1 files changed, 69 insertions(+), 86 deletions(-)

diff --git a/kernel/rcupreempt_trace.c b/kernel/rcupreempt_trace.c
index 7c2665c..a0c8297 100644
--- a/kernel/rcupreempt_trace.c
+++ b/kernel/rcupreempt_trace.c
@@ -39,13 +39,9 @@
 #include <linux/percpu.h>
 #include <linux/notifier.h>
 #include <linux/cpu.h>
-#include <linux/mutex.h>
 #include <linux/rcupreempt_trace.h>
 #include <linux/debugfs.h>
-
-static struct mutex rcupreempt_trace_mutex;
-static char *rcupreempt_trace_buf;
-#define RCUPREEMPT_TRACE_BUF_SIZE 4096
+#include <linux/seq_file.h>
 
 void rcupreempt_trace_move2done(struct rcupreempt_trace *trace)
 {
@@ -170,110 +166,107 @@ static void rcupreempt_trace_sum(struct rcupreempt_trace *sp)
 	}
 }
 
-static ssize_t rcustats_read(struct file *filp, char __user *buffer,
-				size_t count, loff_t *ppos)
+static ssize_t show_rcustats(struct seq_file *m, void *unused)
 {
 	struct rcupreempt_trace trace;
-	ssize_t bcount;
-	int cnt = 0;
 
 	rcupreempt_trace_sum(&trace);
-	mutex_lock(&rcupreempt_trace_mutex);
-	snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE - cnt,
-		 "ggp=%ld rcc=%ld\n",
-		 rcu_batches_completed(),
-		 trace.rcu_check_callbacks);
-	snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE - cnt,
-		 "na=%ld nl=%ld wa=%ld wl=%ld da=%ld dl=%ld dr=%ld di=%d\n"
-		 "1=%d e1=%d i1=%ld ie1=%ld g1=%ld a1=%ld ae1=%ld a2=%ld\n"
-		 "z1=%ld ze1=%ld z2=%ld m1=%ld me1=%ld m2=%ld\n",
 
-		 trace.next_add, trace.next_length,
-		 trace.wait_add, trace.wait_length,
-		 trace.done_add, trace.done_length,
-		 trace.done_remove, atomic_read(&trace.done_invoked),
-		 atomic_read(&trace.rcu_try_flip_1),
-		 atomic_read(&trace.rcu_try_flip_e1),
-		 trace.rcu_try_flip_i1, trace.rcu_try_flip_ie1,
-		 trace.rcu_try_flip_g1,
-		 trace.rcu_try_flip_a1, trace.rcu_try_flip_ae1,
+	seq_printf(m, "ggp=%ld rcc=%ld\n",
+		   rcu_batches_completed(),
+		   trace.rcu_check_callbacks);
+
+	seq_printf(m, "na=%ld nl=%ld wa=%ld wl=%ld da=%ld dl=%ld dr=%ld di=%d\n"
+		      "1=%d e1=%d i1=%ld ie1=%ld g1=%ld a1=%ld ae1=%ld a2=%ld\n"
+		      "z1=%ld ze1=%ld z2=%ld m1=%ld me1=%ld m2=%ld\n",
+		   trace.next_add, trace.next_length,
+		   trace.wait_add, trace.wait_length,
+		   trace.done_add, trace.done_length,
+		   trace.done_remove, atomic_read(&trace.done_invoked),
+		   atomic_read(&trace.rcu_try_flip_1),
+		   atomic_read(&trace.rcu_try_flip_e1),
+		   trace.rcu_try_flip_i1, trace.rcu_try_flip_ie1,
+		   trace.rcu_try_flip_g1,
+		   trace.rcu_try_flip_a1, trace.rcu_try_flip_ae1,
 			 trace.rcu_try_flip_a2,
-		 trace.rcu_try_flip_z1, trace.rcu_try_flip_ze1,
+		   trace.rcu_try_flip_z1, trace.rcu_try_flip_ze1,
 			 trace.rcu_try_flip_z2,
-		 trace.rcu_try_flip_m1, trace.rcu_try_flip_me1,
-			trace.rcu_try_flip_m2);
-	bcount = simple_read_from_buffer(buffer, count, ppos,
-			rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
-	mutex_unlock(&rcupreempt_trace_mutex);
-	return bcount;
+		   trace.rcu_try_flip_m1, trace.rcu_try_flip_me1,
+			 trace.rcu_try_flip_m2);
+
+	return 0;
+}
+
+static int rcustats_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, show_rcustats, NULL);
 }
 
-static ssize_t rcugp_read(struct file *filp, char __user *buffer,
-				size_t count, loff_t *ppos)
+static ssize_t show_rcugp(struct seq_file *m, void *unused)
 {
 	long oldgp = rcu_batches_completed();
-	ssize_t bcount;
 
-	mutex_lock(&rcupreempt_trace_mutex);
 	synchronize_rcu();
-	snprintf(rcupreempt_trace_buf, RCUPREEMPT_TRACE_BUF_SIZE,
-		"oldggp=%ld  newggp=%ld\n", oldgp, rcu_batches_completed());
-	bcount = simple_read_from_buffer(buffer, count, ppos,
-			rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
-	mutex_unlock(&rcupreempt_trace_mutex);
-	return bcount;
+	seq_printf(m, "oldggp=%ld  newggp=%ld\n",
+		   oldgp, rcu_batches_completed());
+
+	return 0;
 }
 
-static ssize_t rcuctrs_read(struct file *filp, char __user *buffer,
-				size_t count, loff_t *ppos)
+static int rcugp_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, show_rcugp, NULL);
+}
+
+static ssize_t show_rcuctrs(struct seq_file *m, void *unused)
 {
-	int cnt = 0;
 	int cpu;
 	int f = rcu_batches_completed() & 0x1;
-	ssize_t bcount;
-
-	mutex_lock(&rcupreempt_trace_mutex);
 
-	cnt += snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE,
-				"CPU last cur F M\n");
+	seq_puts(m, "CPU last cur F M\n");
 	for_each_online_cpu(cpu) {
 		long *flipctr = rcupreempt_flipctr(cpu);
-		cnt += snprintf(&rcupreempt_trace_buf[cnt],
-				RCUPREEMPT_TRACE_BUF_SIZE - cnt,
-					"%3d %4ld %3ld %d %d\n",
-			       cpu,
-			       flipctr[!f],
-			       flipctr[f],
-			       rcupreempt_flip_flag(cpu),
-			       rcupreempt_mb_flag(cpu));
+		seq_printf(m, "%3d %4ld %3ld %d %d\n",
+			   cpu,
+			   flipctr[!f],
+			   flipctr[f],
+			   rcupreempt_flip_flag(cpu),
+			   rcupreempt_mb_flag(cpu));
 	}
-	cnt += snprintf(&rcupreempt_trace_buf[cnt],
-			RCUPREEMPT_TRACE_BUF_SIZE - cnt,
-			"ggp = %ld, state = %s\n",
-			rcu_batches_completed(),
-			rcupreempt_try_flip_state_name());
-	cnt += snprintf(&rcupreempt_trace_buf[cnt],
-			RCUPREEMPT_TRACE_BUF_SIZE - cnt,
-			"\n");
-	bcount = simple_read_from_buffer(buffer, count, ppos,
-			rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
-	mutex_unlock(&rcupreempt_trace_mutex);
-	return bcount;
+	seq_printf(m, "ggp = %ld, state = %s\n",
+		   rcu_batches_completed(),
+		   rcupreempt_try_flip_state_name());
+
+	return 0;
+}
+
+static int rcuctrs_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, show_rcuctrs, NULL);
 }
 
 static struct file_operations rcustats_fops = {
 	.owner = THIS_MODULE,
-	.read = rcustats_read,
+	.open = rcustats_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
 };
 
 static struct file_operations rcugp_fops = {
 	.owner = THIS_MODULE,
-	.read = rcugp_read,
+	.open = rcugp_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
 };
 
 static struct file_operations rcuctrs_fops = {
 	.owner = THIS_MODULE,
-	.read = rcuctrs_read,
+	.open = rcuctrs_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
 };
 
 static struct dentry *rcudir, *statdir, *ctrsdir, *gpdir;
@@ -308,16 +301,7 @@ out:
 
 static int __init rcupreempt_trace_init(void)
 {
-	int ret;
-
-	mutex_init(&rcupreempt_trace_mutex);
-	rcupreempt_trace_buf = kmalloc(RCUPREEMPT_TRACE_BUF_SIZE, GFP_KERNEL);
-	if (!rcupreempt_trace_buf)
-		return 1;
-	ret = rcupreempt_debugfs_init();
-	if (ret)
-		kfree(rcupreempt_trace_buf);
-	return ret;
+	return rcupreempt_debugfs_init();
 }
 
 static void __exit rcupreempt_trace_cleanup(void)
@@ -326,7 +310,6 @@ static void __exit rcupreempt_trace_cleanup(void)
 	debugfs_remove(gpdir);
 	debugfs_remove(ctrsdir);
 	debugfs_remove(rcudir);
-	kfree(rcupreempt_trace_buf);
 }
 
 
-- 
1.5.4.rc3