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Subject[PATCH] 1/1: Device-Mapper: Remove 1024 devices limitation
Date
Remove the limitation of 1024 DM devices.

Signed-off-by: Kevin Corry <kevcorry@us.ibm.com>

--- diff/drivers/md/dm.c 2004-06-30 08:45:34.512303600 -0500
+++ source/drivers/md/dm.c 2004-06-30 08:48:42.085788096 -0500
@@ -17,11 +17,13 @@
#include <linux/slab.h>

static const char *_name = DM_NAME;
-#define MAX_DEVICES 1024

static unsigned int major = 0;
static unsigned int _major = 0;

+static int realloc_minor_bits(unsigned long requested_minor);
+static void free_minor_bits(void);
+
/*
* One of these is allocated per bio.
*/
@@ -111,11 +113,19 @@
return -ENOMEM;
}

+ r = realloc_minor_bits(1024);
+ if (r < 0) {
+ kmem_cache_destroy(_tio_cache);
+ kmem_cache_destroy(_io_cache);
+ return r;
+ }
+
_major = major;
r = register_blkdev(_major, _name);
if (r < 0) {
kmem_cache_destroy(_tio_cache);
kmem_cache_destroy(_io_cache);
+ free_minor_bits();
return r;
}

@@ -129,6 +139,7 @@
{
kmem_cache_destroy(_tio_cache);
kmem_cache_destroy(_io_cache);
+ free_minor_bits();

if (unregister_blkdev(_major, _name) < 0)
DMERR("devfs_unregister_blkdev failed");
@@ -615,14 +626,58 @@
/*-----------------------------------------------------------------
* A bitset is used to keep track of allocated minor numbers.
*---------------------------------------------------------------*/
-static spinlock_t _minor_lock = SPIN_LOCK_UNLOCKED;
-static unsigned long _minor_bits[MAX_DEVICES / BITS_PER_LONG];
+static DECLARE_MUTEX(_minor_lock);
+static unsigned long *_minor_bits = NULL;
+static unsigned long _max_minors = 0;
+
+#define MINORS_SIZE(minors) ((minors / BITS_PER_LONG) * sizeof(unsigned long))
+
+static int realloc_minor_bits(unsigned long requested_minor)
+{
+ unsigned long max_minors;
+ unsigned long *minor_bits, *tmp;
+
+ if (requested_minor < _max_minors)
+ return -EINVAL;
+
+ /* Round up the requested minor to the next power-of-2. */
+ max_minors = 1 << fls(requested_minor - 1);
+ if (max_minors > (1 << MINORBITS))
+ return -EINVAL;
+
+ minor_bits = kmalloc(MINORS_SIZE(max_minors), GFP_KERNEL);
+ if (!minor_bits)
+ return -ENOMEM;
+ memset(minor_bits, 0, MINORS_SIZE(max_minors));
+
+ /* Copy the existing bit-set to the new one. */
+ if (_minor_bits)
+ memcpy(minor_bits, _minor_bits, MINORS_SIZE(_max_minors));
+
+ tmp = _minor_bits;
+ _minor_bits = minor_bits;
+ _max_minors = max_minors;
+ if (tmp)
+ kfree(tmp);
+
+ return 0;
+}
+
+static void free_minor_bits(void)
+{
+ down(&_minor_lock);
+ kfree(_minor_bits);
+ _minor_bits = NULL;
+ _max_minors = 0;
+ up(&_minor_lock);
+}

static void free_minor(unsigned int minor)
{
- spin_lock(&_minor_lock);
- clear_bit(minor, _minor_bits);
- spin_unlock(&_minor_lock);
+ down(&_minor_lock);
+ if (minor < _max_minors)
+ clear_bit(minor, _minor_bits);
+ up(&_minor_lock);
}

/*
@@ -630,37 +685,48 @@
*/
static int specific_minor(unsigned int minor)
{
- int r = -EBUSY;
+ int r = 0;

- if (minor >= MAX_DEVICES) {
- DMWARN("request for a mapped_device beyond MAX_DEVICES (%d)",
- MAX_DEVICES);
+ if (minor > (1 << MINORBITS))
return -EINVAL;
+
+ down(&_minor_lock);
+ if (minor >= _max_minors) {
+ r = realloc_minor_bits(minor);
+ if (r) {
+ up(&_minor_lock);
+ return r;
+ }
}

- spin_lock(&_minor_lock);
- if (!test_and_set_bit(minor, _minor_bits))
- r = 0;
- spin_unlock(&_minor_lock);
+ if (test_and_set_bit(minor, _minor_bits))
+ r = -EBUSY;
+ up(&_minor_lock);

return r;
}

static int next_free_minor(unsigned int *minor)
{
- int r = -EBUSY;
+ int r;
unsigned int m;

- spin_lock(&_minor_lock);
- m = find_first_zero_bit(_minor_bits, MAX_DEVICES);
- if (m != MAX_DEVICES) {
- set_bit(m, _minor_bits);
- *minor = m;
- r = 0;
+ down(&_minor_lock);
+ m = find_first_zero_bit(_minor_bits, _max_minors);
+ if (m >= _max_minors) {
+ r = realloc_minor_bits(_max_minors * 2);
+ if (r) {
+ up(&_minor_lock);
+ return r;
+ }
+ m = find_first_zero_bit(_minor_bits, _max_minors);
}
- spin_unlock(&_minor_lock);

- return r;
+ set_bit(m, _minor_bits);
+ *minor = m;
+ up(&_minor_lock);
+
+ return 0;
}

static struct block_device_operations dm_blk_dops;
-
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