RAS, debugfs: Add debugfs interface for RAS subsystem

Implement a new debugfs interface for RAS susbsystem.
A file named daemon_active is added there accordingly.
This file is used to track if user space daemon accesses
perf/trace interface or not. One can track which daemon
opens it via "lsof /path/to/debugfs/ras/daemon_active".

Signed-off-by: Chen, Gong <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Borislav Petkov <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>

drivers/ras/Makefile

···
-obj-$(CONFIG_RAS) += ras.o
+obj-$(CONFIG_RAS) += ras.o debugfs.o

drivers/ras/debugfs.c

···
+#include <linux/debugfs.h>
+
+static struct dentry *ras_debugfs_dir;
+
+static atomic_t trace_count = ATOMIC_INIT(0);
+
+int ras_userspace_consumers(void)
+{
+	return atomic_read(&trace_count);
+}
+EXPORT_SYMBOL_GPL(ras_userspace_consumers);
+
+static int trace_show(struct seq_file *m, void *v)
+{
+	return atomic_read(&trace_count);
+}
+
+static int trace_open(struct inode *inode, struct file *file)
+{
+	atomic_inc(&trace_count);
+	return single_open(file, trace_show, NULL);
+}
+
+static int trace_release(struct inode *inode, struct file *file)
+{
+	atomic_dec(&trace_count);
+	return single_release(inode, file);
+}
+
+static const struct file_operations trace_fops = {
+	.open    = trace_open,
+	.read    = seq_read,
+	.llseek  = seq_lseek,
+	.release = trace_release,
+};
+
+int __init ras_add_daemon_trace(void)
+{
+	struct dentry *fentry;
+
+	if (!ras_debugfs_dir)
+		return -ENOENT;
+
+	fentry = debugfs_create_file("daemon_active", S_IRUSR, ras_debugfs_dir,
+				     NULL, &trace_fops);
+	if (!fentry)
+		return -ENODEV;
+
+	return 0;
+
+}
+
+void __init ras_debugfs_init(void)
+{
+	ras_debugfs_dir = debugfs_create_dir("ras", NULL);
+}

drivers/ras/ras.c

···
  *	Chen, Gong <[e-mail]>
  */
 
+#include <linux/init.h>
+#include <linux/ras.h>
+
 #define CREATE_TRACE_POINTS
 #define TRACE_INCLUDE_PATH ../../include/ras
 #include <ras/ras_event.h>
+
+static int __init ras_init(void)
+{
+	int rc = 0;
+
+	ras_debugfs_init();
+	rc = ras_add_daemon_trace();
+
+	return rc;
+}
+subsys_initcall(ras_init);
 
 EXPORT_TRACEPOINT_SYMBOL_GPL(mc_event);

include/linux/ras.h

···
+#ifndef __RAS_H__
+#define __RAS_H__
+
+#ifdef CONFIG_DEBUG_FS
+int ras_userspace_consumers(void);
+void ras_debugfs_init(void);
+int ras_add_daemon_trace(void);
+#else
+static inline int ras_userspace_consumers(void) { return 0; }
+static inline void ras_debugfs_init(void) { return; }
+static inline int ras_add_daemon_trace(void) { return 0; }
+#endif
+
+#endif