root/include/linux/blockgroup_lock.h

DEFINITIONS

1. bgl_lock_init
2. bgl_lock_ptr

#ifndef _LINUX_BLOCKGROUP_LOCK_H
#define _LINUX_BLOCKGROUP_LOCK_H
/*
 * Per-blockgroup locking for ext2 and ext3.
 *
 * Simple hashed spinlocking.
 */

#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
 */
static inline spinlock_t *
bgl_lock_ptr(struct blockgroup_lock *bgl, unsigned int block_group)
{
        return &bgl->locks[(block_group) & (NR_BG_LOCKS-1)].lock;
}

#endif