linux-kernel - [PATCH 2/2] char_dev: order /proc/devices by major number

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Date:   Thu, 15 Jun 2017 14:05:21 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alan Cox <alan@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: [PATCH 2/2] 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 <logang@...tatee.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Alan Cox <alan@...ux.intel.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Linus Walleij <linus.walleij@...aro.org>
---
 fs/char_dev.c      | 17 +++++++++++++----
 fs/proc/devices.c  |  8 ++++----
 include/linux/fs.h |  2 +-
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index c9d18362e89d..ebcc8fb3fa66 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -28,6 +28,8 @@ static struct kobj_map *cdev_map;
 
 static DEFINE_MUTEX(chrdevs_lock);
 
+#define CHRDEV_MAJOR_HASH_SIZE 255
+
 static struct char_device_struct {
 	struct char_device_struct *next;
 	unsigned int major;
@@ -49,12 +51,12 @@ void chrdev_show(struct seq_file *f, off_t offset)
 {
 	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 */
@@ -117,6 +119,13 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor,
 		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;
 	cd->baseminor = baseminor;
 	cd->minorct = minorct;
diff --git a/fs/proc/devices.c b/fs/proc/devices.c
index 50493edc30e5..d196e22c4f1c 100644
--- a/fs/proc/devices.c
+++ b/fs/proc/devices.c
@@ -7,14 +7,14 @@ static int devinfo_show(struct seq_file *f, void *v)
 {
 	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);
@@ -25,7 +25,7 @@ static int devinfo_show(struct seq_file *f, void *v)
 
 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;
 }
@@ -33,7 +33,7 @@ static void *devinfo_start(struct seq_file *f, loff_t *pos)
 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;
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 34a8482728d1..f1347c2ca3e9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2445,7 +2445,7 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev,
 #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 */
-- 
2.11.0