[rfc 3/4] fs, eventfd: Add procfs fdinfo helper

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This allow us to print out raw counter value.
So the /proc/pid/fdinfo/fd look like

 | pos:	0
 | flags:	04002
 | eventfd-count:               5a

Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
---
 fs/eventfd.c |   57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

Index: linux-2.6.git/fs/eventfd.c
===================================================================
--- linux-2.6.git.orig/fs/eventfd.c
+++ linux-2.6.git/fs/eventfd.c
@@ -19,6 +19,8 @@
 #include <linux/export.h>
 #include <linux/kref.h>
 #include <linux/eventfd.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
 
 struct eventfd_ctx {
 	struct kref kref;
@@ -437,3 +439,58 @@ SYSCALL_DEFINE1(eventfd, unsigned int, c
 	return sys_eventfd2(count, 0);
 }
 
+#ifdef CONFIG_PROC_FS
+
+static void *seq_start(struct seq_file *m, loff_t *pos)
+{
+	struct proc_fdinfo_extra *extra = m->private;
+	return *pos == 1 ? extra->fd_file : NULL;
+}
+
+static void seq_stop(struct seq_file *m, void *v)
+{
+}
+
+static void *seq_next(struct seq_file *m, void *p, loff_t *pos)
+{
+	struct proc_fdinfo_extra *extra = m->private;
+	return ++*pos == 1 ? extra->fd_file : NULL;
+}
+
+static int seq_show(struct seq_file *m, void *v)
+{
+	struct eventfd_ctx *ctx = ((struct file *)v)->private_data;
+
+	spin_lock_irq(&ctx->wqh.lock);
+	seq_printf(m, "eventfd-count: %16llx\n",
+		   (unsigned long long)ctx->count);
+	spin_unlock_irq(&ctx->wqh.lock);
+
+	return 0;
+}
+
+static const struct seq_operations eventfd_fdinfo_ops = {
+	.start	= seq_start,
+	.next	= seq_next,
+	.stop	= seq_stop,
+	.show	= seq_show,
+};
+
+static int eventfd_fdinfo_probe(struct file *file)
+{
+	return file->f_op == &eventfd_fops;
+}
+
+static struct proc_fdinfo_helper eventfd_fdinfo_helper = {
+	.name	= "evetfd",
+	.ops	= &eventfd_fdinfo_ops,
+	.probe	= eventfd_fdinfo_probe,
+};
+
+static int __init eventfd_init(void)
+{
+	return proc_register_fdinfo_helper(&eventfd_fdinfo_helper);
+}
+fs_initcall(eventfd_init);
+
+#endif /* CONFIG_PROC_FS */

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