char_dev: order /proc/devices by major number

Presently, the order of the char devices listed in /proc/devices is not
entirely sequential. If a char device has a major number greater than
CHRDEV_MAJOR_HASH_SIZE (255), it will be ordered as if its major were
module 255. For example, 511 appears after 1.

This patch cleans that up and prints each major number in the correct
order, regardless of where they are stored in the hash table.

In order to do this, we introduce CHRDEV_MAJOR_MAX as an artificial
limit (chosen to be 511). It will then print all devices in major
order number from 0 to the maximum.

Signed-off-by: Logan Gunthorpe <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Alan Cox <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Linus Walleij <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

fs/char_dev.c

···
 
 static DEFINE_MUTEX(chrdevs_lock);
 
+#define CHRDEV_MAJOR_HASH_SIZE 255
+
 static struct char_device_struct {
 	struct char_device_struct *next;
 	unsigned int major;
···
 {
 	struct char_device_struct *cd;
 
-	if (offset < CHRDEV_MAJOR_HASH_SIZE) {
-		mutex_lock(&chrdevs_lock);
-		for (cd = chrdevs[offset]; cd; cd = cd->next)
+	mutex_lock(&chrdevs_lock);
+	for (cd = chrdevs[major_to_index(offset)]; cd; cd = cd->next) {
+		if (cd->major == offset)
 			seq_printf(f, "%3d %s\n", cd->major, cd->name);
-		mutex_unlock(&chrdevs_lock);
 	}
+	mutex_unlock(&chrdevs_lock);
 }
 
 #endif /* CONFIG_PROC_FS */
···
 			goto out;
 		}
 		major = ret;
+	}
+
+	if (major >= CHRDEV_MAJOR_MAX) {
+		pr_err("CHRDEV \"%s\" major requested (%d) is greater than the maximum (%d)\n",
+		       name, major, CHRDEV_MAJOR_MAX);
+		ret = -EINVAL;
+		goto out;
 	}
 
 	cd->major = major;

fs/proc/devices.c

···
 {
 	int i = *(loff_t *) v;
 
-	if (i < CHRDEV_MAJOR_HASH_SIZE) {
+	if (i < CHRDEV_MAJOR_MAX) {
 		if (i == 0)
 			seq_puts(f, "Character devices:\n");
 		chrdev_show(f, i);
 	}
 #ifdef CONFIG_BLOCK
 	else {
-		i -= CHRDEV_MAJOR_HASH_SIZE;
+		i -= CHRDEV_MAJOR_MAX;
 		if (i == 0)
 			seq_puts(f, "\nBlock devices:\n");
 		blkdev_show(f, i);
···
 
 static void *devinfo_start(struct seq_file *f, loff_t *pos)
 {
-	if (*pos < (BLKDEV_MAJOR_HASH_SIZE + CHRDEV_MAJOR_HASH_SIZE))
+	if (*pos < (BLKDEV_MAJOR_HASH_SIZE + CHRDEV_MAJOR_MAX))
 		return pos;
 	return NULL;
 }
···
 static void *devinfo_next(struct seq_file *f, void *v, loff_t *pos)
 {
 	(*pos)++;
-	if (*pos >= (BLKDEV_MAJOR_HASH_SIZE + CHRDEV_MAJOR_HASH_SIZE))
+	if (*pos >= (BLKDEV_MAJOR_HASH_SIZE + CHRDEV_MAJOR_MAX))
 		return NULL;
 	return pos;
 }

include/linux/fs.h

···
 #endif
 
 /* fs/char_dev.c */
-#define CHRDEV_MAJOR_HASH_SIZE	255
+#define CHRDEV_MAJOR_MAX 512
 /* Marks the bottom of the first segment of free char majors */
 #define CHRDEV_MAJOR_DYN_END 234
 /* Marks the top and bottom of the second segment of free char majors */