[PATCH 01/19] char_dev: replace cdev_map with an xarray

From: Christoph Hellwig <hch@lst.de>
To: Jens Axboe <axboe@kernel.dk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Denis Efremov <efremov@linux.com>,
	"David S. Miller" <davem@davemloft.net>,
	Song Liu <song@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>,
	Finn Thain <fthain@telegraphics.com.au>,
	Michael Schmitz <schmitzmic@gmail.com>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-ide@vger.kernel.org, linux-raid@vger.kernel.org,
	linux-scsi@vger.kernel.org, linux-m68k@lists.linux-m68k.org
Subject: [PATCH 01/19] char_dev: replace cdev_map with an xarray
Date: Thu,  3 Sep 2020 10:01:01 +0200	[thread overview]
Message-ID: <20200903080119.441674-2-hch@lst.de> (raw)
In-Reply-To: <20200903080119.441674-1-hch@lst.de>

None of the complicated overlapping regions bits of the kobj_map are
required for the character device lookup, so just a trivial xarray
instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/char_dev.c | 94 +++++++++++++++++++++++++--------------------------
 fs/dcache.c   |  1 -
 fs/internal.h |  5 ---
 3 files changed, 47 insertions(+), 53 deletions(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index ba0ded7842a779..f9a983d2d1a975 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -17,7 +17,6 @@
 #include <linux/seq_file.h>
 
 #include <linux/kobject.h>
-#include <linux/kobj_map.h>
 #include <linux/cdev.h>
 #include <linux/mutex.h>
 #include <linux/backing-dev.h>
@@ -25,8 +24,7 @@
 
 #include "internal.h"
 
-static struct kobj_map *cdev_map;
-
+static DEFINE_XARRAY(cdev_map);
 static DEFINE_MUTEX(chrdevs_lock);
 
 #define CHRDEV_MAJOR_HASH_SIZE 255
@@ -367,6 +365,29 @@ void cdev_put(struct cdev *p)
 	}
 }
 
+static struct cdev *cdev_lookup(dev_t dev)
+{
+	struct cdev *cdev;
+
+retry:
+	mutex_lock(&chrdevs_lock);
+	cdev = xa_load(&cdev_map, dev);
+	if (!cdev) {
+		mutex_unlock(&chrdevs_lock);
+
+		if (request_module("char-major-%d-%d",
+				   MAJOR(dev), MINOR(dev)) > 0)
+			/* Make old-style 2.4 aliases work */
+			request_module("char-major-%d", MAJOR(dev));
+		goto retry;
+	}
+
+	if (!cdev_get(cdev))
+		cdev = NULL;
+	mutex_unlock(&chrdevs_lock);
+	return cdev;
+}
+
 /*
  * Called every time a character special file is opened
  */
@@ -380,13 +401,10 @@ static int chrdev_open(struct inode *inode, struct file *filp)
 	spin_lock(&cdev_lock);
 	p = inode->i_cdev;
 	if (!p) {
-		struct kobject *kobj;
-		int idx;
 		spin_unlock(&cdev_lock);
-		kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
-		if (!kobj)
+		new = cdev_lookup(inode->i_rdev);
+		if (!new)
 			return -ENXIO;
-		new = container_of(kobj, struct cdev, kobj);
 		spin_lock(&cdev_lock);
 		/* Check i_cdev again in case somebody beat us to it while
 		   we dropped the lock. */
@@ -454,18 +472,6 @@ const struct file_operations def_chr_fops = {
 	.llseek = noop_llseek,
 };
 
-static struct kobject *exact_match(dev_t dev, int *part, void *data)
-{
-	struct cdev *p = data;
-	return &p->kobj;
-}
-
-static int exact_lock(dev_t dev, void *data)
-{
-	struct cdev *p = data;
-	return cdev_get(p) ? 0 : -1;
-}
-
 /**
  * cdev_add() - add a char device to the system
  * @p: the cdev structure for the device
@@ -478,7 +484,7 @@ static int exact_lock(dev_t dev, void *data)
  */
 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 {
-	int error;
+	int error, i;
 
 	p->dev = dev;
 	p->count = count;
@@ -486,14 +492,22 @@ int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 	if (WARN_ON(dev == WHITEOUT_DEV))
 		return -EBUSY;
 
-	error = kobj_map(cdev_map, dev, count, NULL,
-			 exact_match, exact_lock, p);
-	if (error)
-		return error;
+	mutex_lock(&chrdevs_lock);
+	for (i = 0; i < count; i++) {
+		error = xa_insert(&cdev_map, dev + i, p, GFP_KERNEL);
+		if (error)
+			goto out_unwind;
+	}
+	mutex_unlock(&chrdevs_lock);
 
 	kobject_get(p->kobj.parent);
-
 	return 0;
+
+out_unwind:
+	while (--i >= 0)
+		xa_erase(&cdev_map, dev + i);
+	mutex_unlock(&chrdevs_lock);
+	return error;
 }
 
 /**
@@ -575,11 +589,6 @@ void cdev_device_del(struct cdev *cdev, struct device *dev)
 		cdev_del(cdev);
 }
 
-static void cdev_unmap(dev_t dev, unsigned count)
-{
-	kobj_unmap(cdev_map, dev, count);
-}
-
 /**
  * cdev_del() - remove a cdev from the system
  * @p: the cdev structure to be removed
@@ -593,11 +602,16 @@ static void cdev_unmap(dev_t dev, unsigned count)
  */
 void cdev_del(struct cdev *p)
 {
-	cdev_unmap(p->dev, p->count);
+	int i;
+
+	mutex_lock(&chrdevs_lock);
+	for (i = 0; i < p->count; i++)
+		xa_erase(&cdev_map, p->dev + i);
+	mutex_unlock(&chrdevs_lock);
+
 	kobject_put(&p->kobj);
 }
 
-
 static void cdev_default_release(struct kobject *kobj)
 {
 	struct cdev *p = container_of(kobj, struct cdev, kobj);
@@ -656,20 +670,6 @@ void cdev_init(struct cdev *cdev, const struct file_operations *fops)
 	cdev->ops = fops;
 }
 
-static struct kobject *base_probe(dev_t dev, int *part, void *data)
-{
-	if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
-		/* Make old-style 2.4 aliases work */
-		request_module("char-major-%d", MAJOR(dev));
-	return NULL;
-}
-
-void __init chrdev_init(void)
-{
-	cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
-}
-
-
 /* Let modules do char dev stuff */
 EXPORT_SYMBOL(register_chrdev_region);
 EXPORT_SYMBOL(unregister_chrdev_region);
diff --git a/fs/dcache.c b/fs/dcache.c
index ea0485861d9377..55e534ad6f8f7f 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3233,5 +3233,4 @@ void __init vfs_caches_init(void)
 	files_maxfiles_init();
 	mnt_init();
 	bdev_cache_init();
-	chrdev_init();
 }
diff --git a/fs/internal.h b/fs/internal.h
index 10517ece45167f..110e952e75a8aa 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -54,11 +54,6 @@ static inline void bd_forget(struct inode *inode)
 extern int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
 		get_block_t *get_block, struct iomap *iomap);
 
-/*
- * char_dev.c
- */
-extern void __init chrdev_init(void);
-
 /*
  * fs_context.c
  */
-- 
2.28.0

