Used miscdevice API for sched_trace

This patch changes sched_trace.c to use the miscdevice API
instead of doing all the cdev management ourselves. This remove a
chunk of code and we get sysfs / udev integration for free.

On systems with default udev rules, this will result in a /dev/litmus/log
device being created automatically.

1 files changed, 17 insertions, 55 deletions

diff --git a/litmus/sched_trace.c b/litmus/sched_trace.c
index 87e725a35eb3..ad0b138d4b01 100644
--- a/litmus/sched_trace.c
+++ b/litmus/sched_trace.c
@@ -5,7 +5,7 @@
 #include <linux/semaphore.h>
 
 #include <linux/fs.h>
-#include <linux/cdev.h>
+#include <linux/miscdevice.h>
 #include <asm/uaccess.h>
 #include <linux/module.h>
 #include <linux/sysrq.h>
@@ -15,6 +15,8 @@
 #include <litmus/sched_trace.h>
 #include <litmus/litmus.h>
 
+#define SCHED_TRACE_NAME "litmus/log"
+
 /* Allocate a buffer of about 32k per CPU */
 #define LITMUS_TRACE_BUF_PAGES 8
 #define LITMUS_TRACE_BUF_SIZE (PAGE_SIZE * LITMUS_TRACE_BUF_PAGES * NR_CPUS)
@@ -25,14 +27,6 @@
 /* Max length for one write --- from kernel --- to the buffer */
 #define MSG_SIZE 255
 
-/*
- * Major number for the tracing char device.
- * the major numbes are from the unassigned/local use block
- *
- * set MAJOR to 0 to have it dynamically assigned
- */
-#define LOG_MAJOR       251
-
 /* Inner ring buffer structure */
 typedef struct {
         rwlock_t        del_lock;
@@ -316,54 +310,18 @@ static int log_release(struct inode *in, struct file *filp)
  *
  * Except for opening the device file it uses the same operations as trace_fops.
  */
-struct file_operations log_fops = {
+static struct file_operations log_fops = {
         .owner   = THIS_MODULE,
         .open    = log_open,
         .release = log_release,
         .read    = log_read,
 };
 
-/*
- * Device registration
- */
-static int __init register_buffer_dev(const char* name,
-                                      struct file_operations* fops,
-                                      int major, int count)
-{
-        dev_t trace_dev;
-        struct cdev *cdev;
-        int error = 0;
-
-        if(major) {
-                trace_dev = MKDEV(major, 0);
-                error = register_chrdev_region(trace_dev, count, name);
-        } else {
-                /* dynamically allocate major number */
-                error = alloc_chrdev_region(&trace_dev, 0, count, name);
-                major = MAJOR(trace_dev);
-        }
-        if (error) {
-                printk(KERN_WARNING "sched trace: "
-                       "Could not register major/minor number %d\n", major);
-                return error;
-        }
-        cdev = cdev_alloc();
-        if (!cdev) {
-                printk(KERN_WARNING "sched trace: "
-                        "Could not get a cdev for %s.\n", name);
-                return -ENOMEM;
-        }
-        cdev->owner = THIS_MODULE;
-        cdev->ops   = fops;
-        error = cdev_add(cdev, trace_dev, count);
-        if (error) {
-                printk(KERN_WARNING "sched trace: "
-                        "add_cdev failed for %s.\n", name);
-                return -ENOMEM;
-        }
-        return error;
-
-}
+static struct miscdevice litmus_log_dev = {
+        .name    = SCHED_TRACE_NAME,
+        .minor   = MISC_DYNAMIC_MINOR,
+        .fops    = &log_fops,
+};
 
 #ifdef CONFIG_MAGIC_SYSRQ
 void dump_trace_buffer(int max)
@@ -372,7 +330,7 @@ void dump_trace_buffer(int max)
         int len;
         int count = 0;
 
-        /* potentially, but very unlikely race... */
+        /* potential, but very unlikely, race... */
         trace_recurse = 1;
         while ((max == 0 || count++ < max) &&
                (len = rb_get(&log_buffer.buf, line, sizeof(line) - 1)) > 0) {
@@ -408,9 +366,13 @@ static int __init init_sched_trace(void)
 #endif
 
 
-        return register_buffer_dev("litmus_log", &log_fops,
-                                   LOG_MAJOR, 1);
+        return misc_register(&litmus_log_dev);
 }
 
-module_init(init_sched_trace);
+static void __exit exit_sched_trace(void)
+{
+        misc_deregister(&litmus_log_dev);
+}
 
+module_init(init_sched_trace);
+module_exit(exit_sched_trace);