perf_counter: SIGIO support

Provide support for fcntl() I/O availability signals.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090406094517.579788800@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/perf_counter.h

@@ -238,6 +238,7 @@ enum perf_event_type {
 #include <linux/rcupdate.h>
 #include <linux/spinlock.h>
 #include <linux/hrtimer.h>
+#include <linux/fs.h>
 #include <asm/atomic.h>
 
 struct task_struct;
@@ -398,6 +399,7 @@ struct perf_counter {
 
 	/* poll related */
 	wait_queue_head_t		waitq;
+	struct fasync_struct		*fasync;
 	/* optional: for NMIs */
 	struct perf_wakeup_entry	wakeup;
 

kernel/perf_counter.c

@@ -1526,13 +1526,30 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 	return ret;
 }
 
+static int perf_fasync(int fd, struct file *filp, int on)
+{
+	struct perf_counter *counter = filp->private_data;
+	struct inode *inode = filp->f_path.dentry->d_inode;
+	int retval;
+
+	mutex_lock(&inode->i_mutex);
+	retval = fasync_helper(fd, filp, on, &counter->fasync);
+	mutex_unlock(&inode->i_mutex);
+
+	if (retval < 0)
+		return retval;
+
+	return 0;
+}
+
 static const struct file_operations perf_fops = {
 	.release		= perf_release,
 	.read			= perf_read,
 	.poll			= perf_poll,
 	.unlocked_ioctl		= perf_ioctl,
 	.compat_ioctl		= perf_ioctl,
 	.mmap			= perf_mmap,
+	.fasync			= perf_fasync,
 };
 
 /*
@@ -1549,7 +1566,7 @@ void perf_counter_wakeup(struct perf_counter *counter)
 	rcu_read_lock();
 	data = rcu_dereference(counter->data);
 	if (data) {
-		(void)atomic_xchg(&data->wakeup, POLL_IN);
+		atomic_set(&data->wakeup, POLL_IN);
 		/*
 		 * Ensure all data writes are issued before updating the
 		 * user-space data head information. The matching rmb()
@@ -1561,6 +1578,7 @@ void perf_counter_wakeup(struct perf_counter *counter)
 	rcu_read_unlock();
 
 	wake_up_all(&counter->waitq);
+	kill_fasync(&counter->fasync, SIGIO, POLL_IN);
 }
 
 /*