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422 giacomo 1
/*
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 * Per-blockgroup locking for ext2 and ext3.
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 *
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 * Simple hashed spinlocking.
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 */
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#include <linux/config.h>
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#include <linux/spinlock.h>
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#include <linux/cache.h>
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#ifdef CONFIG_SMP
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/*
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 * We want a power-of-two.  Is there a better way than this?
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 */
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#if NR_CPUS >= 32
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#define NR_BG_LOCKS     128
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#elif NR_CPUS >= 16
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#define NR_BG_LOCKS     64
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#elif NR_CPUS >= 8
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#define NR_BG_LOCKS     32
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#elif NR_CPUS >= 4
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#define NR_BG_LOCKS     16
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#elif NR_CPUS >= 2
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#define NR_BG_LOCKS     8
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#else
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#define NR_BG_LOCKS     4
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#endif
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#else   /* CONFIG_SMP */
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#define NR_BG_LOCKS     1
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#endif  /* CONFIG_SMP */
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struct bgl_lock {
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        spinlock_t lock;
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} ____cacheline_aligned_in_smp;
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struct blockgroup_lock {
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        struct bgl_lock locks[NR_BG_LOCKS];
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};
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static inline void bgl_lock_init(struct blockgroup_lock *bgl)
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{
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        int i;
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        for (i = 0; i < NR_BG_LOCKS; i++)
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                spin_lock_init(&bgl->locks[i].lock);
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}
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/*
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 * The accessor is a macro so we can embed a blockgroup_lock into different
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 * superblock types
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 */
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#define sb_bgl_lock(sb, block_group) \
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        (&(sb)->s_blockgroup_lock.locks[(block_group) & (NR_BG_LOCKS-1)].lock)
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