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/*

 * Per-blockgroup locking for ext2 and ext3.

 *

 * Simple hashed spinlocking.

 */

#include <linux/config.h>

#include <linux/spinlock.h>

#include <linux/cache.h>

#ifdef CONFIG_SMP

/*

 * We want a power-of-two.  Is there a better way than this?

 */

#if NR_CPUS >= 32

#define NR_BG_LOCKS     128

#elif NR_CPUS >= 16

#define NR_BG_LOCKS     64

#elif NR_CPUS >= 8

#define NR_BG_LOCKS     32

#elif NR_CPUS >= 4

#define NR_BG_LOCKS     16

#elif NR_CPUS >= 2

#define NR_BG_LOCKS     8

#else

#define NR_BG_LOCKS     4

#endif

#else   /* CONFIG_SMP */

#define NR_BG_LOCKS     1

#endif  /* CONFIG_SMP */

struct bgl_lock {

        spinlock_t lock;

} ____cacheline_aligned_in_smp;

struct blockgroup_lock {

        struct bgl_lock locks[NR_BG_LOCKS];

};

static inline void bgl_lock_init(struct blockgroup_lock *bgl)

{

        int i;

        for (i = 0; i < NR_BG_LOCKS; i++)

                spin_lock_init(&bgl->locks[i].lock);

}

/*

 * The accessor is a macro so we can embed a blockgroup_lock into different

 * superblock types

 */

#define sb_bgl_lock(sb, block_group) \

        (&(sb)->s_blockgroup_lock.locks[(block_group) & (NR_BG_LOCKS-1)].lock)