Preliminary udev support

This patch implements support for FeatherTrace devices to use the sysfs
file system and, consequently, udev support. It also changed the
FeatherTrace headers and API a bit. There is still more to do,
including:

- Verify that calling device_create() is the right thing to do (I think
  it is).

- Testing! I noticed some failed FeatherTrace writes, but it was on a
  system with high utilization and in qemu, so it might be benign.

- Remove created devices on system shutdown or module unregister.
  FeaterTrace never did this; probably not a huge issue if we don't.

- Determine if we want to try and use a "root device" to group LITMUS^RT
  devices together. See the __root_device_register() function in
  drivers/base/core.c

- Update documentation.

4 files changed, 56 insertions, 29 deletions

diff --git a/include/litmus/ftdev.h b/include/litmus/ftdev.h
index 7697b4616699..efb2a5c9a9b0 100644
--- a/include/litmus/ftdev.h
+++ b/include/litmus/ftdev.h
@@ -28,10 +28,13 @@ struct ftdev_minor {
         struct mutex            lock;
         /* FIXME: filter for authorized events */
         struct ftdev_event*     events;
+        struct device*          device;
 };
 
 struct ftdev {
         struct cdev             cdev;
+        struct class*           class;
+        const char*             name;
         /* FIXME: don't waste memory, allocate dynamically */
         struct ftdev_minor      minor[MAX_FTDEV_MINORS];
         unsigned int            minor_cnt;
@@ -43,7 +46,7 @@ struct ftdev {
 struct ft_buffer* alloc_ft_buffer(unsigned int count, size_t size);
 void free_ft_buffer(struct ft_buffer* buf);
 
-void ftdev_init(struct ftdev* ftdev, struct module* owner);
-int register_ftdev(struct ftdev* ftdev, const char* name, int major);
+void ftdev_init(struct ftdev* ftdev, struct module* owner, const char* name);
+int register_ftdev(struct ftdev* ftdev);
 
 #endif
diff --git a/litmus/ftdev.c b/litmus/ftdev.c
index 51dafaebf8a6..d68d05c6d7dc 100644
--- a/litmus/ftdev.c
+++ b/litmus/ftdev.c
@@ -4,6 +4,7 @@
 #include <linux/cdev.h>
 #include <asm/uaccess.h>
 #include <linux/module.h>
+#include <linux/device.h>
 
 #include <litmus/litmus.h>
 #include <litmus/feather_trace.h>
@@ -310,10 +311,11 @@ struct file_operations ftdev_fops = {
 };
 
 
-void ftdev_init(struct ftdev* ftdev, struct module* owner)
+void ftdev_init(struct ftdev* ftdev, struct module* owner, const char* name)
 {
-        int i;
+        int i, error;
         cdev_init(&ftdev->cdev, &ftdev_fops);
+        ftdev->name = name;
         ftdev->cdev.owner = owner;
         ftdev->cdev.ops = &ftdev_fops;
         ftdev->minor_cnt  = 0;
@@ -326,35 +328,62 @@ void ftdev_init(struct ftdev* ftdev, struct module* owner)
         ftdev->alloc    = NULL;
         ftdev->free     = NULL;
         ftdev->can_open = NULL;
+
+        ftdev->class = class_create(owner, ftdev->name);
+        if (IS_ERR(ftdev->class)) {
+                error = PTR_ERR(ftdev->class);
+                printk(KERN_WARNING "ftdev(%s): "
+                        "Could not create device class.\n",
+                        name);
+        }
 }
 
-int register_ftdev(struct ftdev* ftdev, const char* name, int major)
+int register_ftdev(struct ftdev* ftdev)
 {
+        struct device **device;
         dev_t   trace_dev;
-        int error = 0;
-
-        if(major) {
-                trace_dev = MKDEV(major, 0);
-                error = register_chrdev_region(trace_dev, ftdev->minor_cnt,
-                                               name);
-        } else {
-                error = alloc_chrdev_region(&trace_dev, 0, ftdev->minor_cnt,
-                                name);
-                major = MAJOR(trace_dev);
-        }
+        int error = 0, major, i;
+
+        error = alloc_chrdev_region(&trace_dev, 0, ftdev->minor_cnt,
+                        ftdev->name);
+        major = MAJOR(trace_dev);
         if (error)
         {
                 printk(KERN_WARNING "ftdev(%s): "
                        "Could not register major/minor number %d/%u\n",
-                       name, major, ftdev->minor_cnt);
-                return error;
+                       ftdev->name, major, ftdev->minor_cnt);
+                goto out;
         }
         error = cdev_add(&ftdev->cdev, trace_dev, ftdev->minor_cnt);
         if (error) {
                 printk(KERN_WARNING "ftdev(%s): "
                        "Could not add cdev for major/minor = %d/%u.\n",
-                       name, major, ftdev->minor_cnt);
-                return error;
+                       ftdev->name, major, ftdev->minor_cnt);
+                goto out;
+        }
+
+        /*
+         * create all the minor devices
+         */
+        for (i = 0; i < ftdev->minor_cnt; ++i)
+        {
+                trace_dev = MKDEV(major, i);
+                device = &(ftdev->minor[i].device);
+
+                *device = device_create(ftdev->class, NULL, trace_dev, NULL,
+                                "%s%d", ftdev->name, i);
+                if (IS_ERR(*device)) {
+                        error = PTR_ERR(*device);
+                        printk(KERN_WARNING "ftdev(%s): "
+                                "Could not create device major/minor number "
+                                "%d/%d\n", ftdev->name, major, i);
+                        printk(KERN_WARNING "ftdev(%s): "
+                                "Will not continue creating devices. Tracing "
+                                "may be in an inconsistent state.\n",
+                                ftdev->name);
+                        goto out;
+                }
         }
+out:
         return error;
 }
diff --git a/litmus/sched_task_trace.c b/litmus/sched_task_trace.c
index e5098ddb1ec9..7ef7b2889b42 100644
--- a/litmus/sched_task_trace.c
+++ b/litmus/sched_task_trace.c
@@ -16,8 +16,6 @@
 #include <litmus/ftdev.h>
 
 
-/* set MAJOR to 0 to have it dynamically assigned */
-#define FT_TASK_TRACE_MAJOR     253
 #define NO_EVENTS               (1 << CONFIG_SCHED_TASK_TRACE_SHIFT)
 
 #define now() litmus_clock()
@@ -44,7 +42,7 @@ static int __init init_sched_task_trace(void)
         printk("Allocated %u sched_trace_xxx() events per CPU "
                "(buffer size: %d bytes)\n",
                NO_EVENTS, (int) sizeof(struct local_buffer));
-        ftdev_init(&st_dev, THIS_MODULE);
+        ftdev_init(&st_dev, THIS_MODULE, "sched_trace");
         for (i = 0; i < NR_CPUS; i++) {
                 buf = &per_cpu(st_event_buffer, i);
                 ok += init_ft_buffer(&buf->ftbuf, NO_EVENTS,
@@ -56,7 +54,7 @@ static int __init init_sched_task_trace(void)
         if (ok == NR_CPUS) {
                 st_dev.minor_cnt = NR_CPUS;
                 st_dev.can_open = st_dev_can_open;
-                return register_ftdev(&st_dev, "sched_trace", FT_TASK_TRACE_MAJOR);
+                return register_ftdev(&st_dev);
         } else {
                 return -EINVAL;
         }
diff --git a/litmus/trace.c b/litmus/trace.c
index b3a6b47aad6e..da650dfe7f4d 100644
--- a/litmus/trace.c
+++ b/litmus/trace.c
@@ -71,9 +71,6 @@ feather_callback void save_timestamp_cpu(unsigned long event,
  */
 #define NO_TIMESTAMPS (2 << 11)
 
-/* set MAJOR to 0 to have it dynamically assigned */
-#define FT_TRACE_MAJOR  252
-
 static int alloc_timestamp_buffer(struct ftdev* ftdev, unsigned int idx)
 {
         unsigned int count = NO_TIMESTAMPS;
@@ -94,11 +91,11 @@ static void free_timestamp_buffer(struct ftdev* ftdev, unsigned int idx)
 static int __init init_ft_overhead_trace(void)
 {
         printk("Initializing Feather-Trace overhead tracing device.\n");
-        ftdev_init(&overhead_dev, THIS_MODULE);
+        ftdev_init(&overhead_dev, THIS_MODULE, "ft_trace");
         overhead_dev.minor_cnt = 1; /* only one buffer */
         overhead_dev.alloc = alloc_timestamp_buffer;
         overhead_dev.free  = free_timestamp_buffer;
-        return register_ftdev(&overhead_dev, "ft_trace", FT_TRACE_MAJOR);
+        return register_ftdev(&overhead_dev);
 }
 
 module_init(init_ft_overhead_trace);