[Xen-devel] [PATCH] have udev create the device for blktap

[Steven Rostedt <srostedt@xxxxxxxxxx>]

This patch makes blktap Do The Right Thing(TM).  It allows udev to 
create the /dev/xen/blktap[0-9] devices.
It creates a sysfs class called "xen".  This part may later be placed 
someplace else, but currently blktap is the only user so it is placed in 
the blktap code.
When blktap is initialized, a blktap0 sysfs class device is made.  The 
other devices blktapX (X > 0) are made when the BLKTAP_IOCTL_NEWINTF 
ioctl is called.  This way we don't flood the sysfs and /dev/xen with 
unnecessary devices.
I added a rule in the xen-backend.rules to allow for udev to create the 
blktap devices.

With this, we can really remove the code to search and create the 
/dev/xen/blktap[0-9]*, but I'll leave it in for now. With the use of 
udev, we really should remove that code as well as the code for creating 
the evtchn device.  udev works for both of these now.  But that removal 
will have to be in another patch.
-- Steve

diff -r 34b6478419b0 linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c
--- a/linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c  Thu Sep 28 08:01:18 
2006 -0400
+++ b/linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c  Thu Sep 28 09:51:45 
2006 -0400
@@ -44,7 +44,6 @@
 #include <linux/kernel.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
-#include <linux/miscdevice.h>
 #include <linux/errno.h>
 #include <linux/major.h>
 #include <linux/gfp.h>
@@ -54,6 +53,30 @@
 
 #define MAX_TAP_DEV 100     /*the maximum number of tapdisk ring devices    */
 #define MAX_DEV_NAME 100    /*the max tapdisk ring device name e.g. blktap0 */
+
+
+struct class *xen_class;
+EXPORT_SYMBOL_GPL(xen_class);
+
+/*
+ * Setup the xen class.  This should probably go in another file, but
+ * since blktap is the only user of it so far, it gets to keep it.
+ */
+int setup_xen_class(void)
+{
+       int ret;
+
+       if (xen_class)
+               return 0;
+
+       xen_class = class_create(THIS_MODULE, "xen");
+       if ((ret = IS_ERR(xen_class))) {
+               xen_class = NULL;
+               return ret;
+       }
+
+       return 0;
+}
 
 /*
  * The maximum number of requests that can be outstanding at any time
@@ -100,6 +123,7 @@ typedef struct tap_blkif {
        unsigned long *idx_map;       /*Record the user ring id to kern 
                                        [req id, idx] tuple                  */
        blkif_t *blkif;               /*Associate blkif with tapdev          */
+       int sysfs_set;                /*Set if it has a class device.        */
 } tap_blkif_t;
 
 /*Data struct handed back to userspace for tapdisk device to VBD mapping*/
@@ -304,8 +328,6 @@ static int blktap_ioctl(struct inode *in
                         unsigned int cmd, unsigned long arg);
 static unsigned int blktap_poll(struct file *file, poll_table *wait);
 
-struct miscdevice *set_misc(int minor, char *name, int dev);
-
 static struct file_operations blktap_fops = {
        .owner   = THIS_MODULE,
        .poll    = blktap_poll,
@@ -337,6 +359,16 @@ static int get_next_free_dev(void)
        
 done:
        spin_unlock_irqrestore(&pending_free_lock, flags);
+
+       /*
+        * We are protected by having the dev_pending set.
+        */
+       if (!tapfds[i]->sysfs_set && xen_class) {
+               class_device_create(xen_class, NULL,
+                                   MKDEV(blktap_major, ret), NULL,
+                                   "blktap%d", ret);
+               tapfds[i]->sysfs_set = 1;
+       }
        return ret;
 }
 
@@ -428,7 +460,7 @@ static int blktap_release(struct inode *
        if (!info) {
                WPRINTK("Trying to free device that doesn't exist "
                       "[/dev/xen/blktap%d]\n",iminor(inode) - BLKTAP_MINOR);
-               return -1;
+               return -EBADF;
        }
        info->dev_inuse = 0;
        DPRINTK("Freeing device [/dev/xen/blktap%d]\n",info->minor);
@@ -602,6 +634,7 @@ static int blktap_ioctl(struct inode *in
        case BLKTAP_IOCTL_FREEINTF:
        {
                unsigned long dev = arg;
+               unsigned long flags;
 
                /* Looking at another device */
                info = NULL;
@@ -609,8 +642,11 @@ static int blktap_ioctl(struct inode *in
                if ( (dev > 0) && (dev < MAX_TAP_DEV) )
                        info = tapfds[dev];
 
+               spin_lock_irqsave(&pending_free_lock, flags);
                if ( (info != NULL) && (info->dev_pending) )
                        info->dev_pending = 0;
+               spin_unlock_irqrestore(&pending_free_lock, flags);
+
                return 0;
        }
        case BLKTAP_IOCTL_MINOR:
@@ -1406,7 +1442,8 @@ static int __init blkif_init(void)
 
        for(i = 0; i < MAX_TAP_DEV; i++ ) {
                info = tapfds[i] = kzalloc(sizeof(tap_blkif_t),GFP_KERNEL);
-               if(tapfds[i] == NULL) return -ENOMEM;
+               if(tapfds[i] == NULL)
+                       return -ENOMEM;
                info->minor = i;
                info->pid = 0;
                info->blkif = NULL;
@@ -1414,12 +1451,31 @@ static int __init blkif_init(void)
                ret = devfs_mk_cdev(MKDEV(blktap_major, i),
                        S_IFCHR|S_IRUGO|S_IWUSR, "xen/blktap%d", i);
 
-               if(ret != 0) return -ENOMEM;
+               if(ret != 0)
+                       return -ENOMEM;
                info->dev_pending = info->dev_inuse = 0;
 
                DPRINTK("Created misc_dev [/dev/xen/blktap%d]\n",i);
        }
        
+       /* Make sure the xen class exists */
+       if (!setup_xen_class()) {
+               /*
+                * This will allow udev to create the blktap ctrl device.
+                * We only want to create blktap0 first.  We don't want
+                * to flood the sysfs system with needless blktap devices.
+                * We only create the device when a request of a new device is
+                * made.
+                */
+               class_device_create(xen_class, NULL,
+                                   MKDEV(blktap_major, 0), NULL,
+                                   "blktap0");
+               tapfds[0]->sysfs_set = 1;
+       } else {
+               /* this is bad, but not fatal */
+               WPRINTK("blktap: sysfs xen_class not created\n");
+       }
+
        DPRINTK("Blktap device successfully created\n");
 
        return 0;
diff -r 34b6478419b0 tools/examples/xen-backend.rules
--- a/tools/examples/xen-backend.rules  Thu Sep 28 08:01:18 2006 -0400
+++ b/tools/examples/xen-backend.rules  Thu Sep 28 09:51:45 2006 -0400
@@ -5,3 +5,4 @@ SUBSYSTEM=="xen-backend", KERNEL=="vif*"
 SUBSYSTEM=="xen-backend", KERNEL=="vif*", ACTION=="offline", 
RUN+="$env{script} offline"
 SUBSYSTEM=="xen-backend", ACTION=="remove", 
RUN+="/etc/xen/scripts/xen-hotplug-cleanup"
 KERNEL=="evtchn", NAME="xen/%k"
+KERNEL=="blktap[0-9]*", NAME="xen/%k"

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