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

Christoph Hellwig
2020-08-30T06:25:03Z

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>
---
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