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    Subject[patch] Add kref_read and kref_put_last primitives
    Greg,
    Here is a patch to add kref_read and kref_put_last.
    These primitives were needed to change files_struct.f_count
    refcounter to use kref api.

    kref_put_last is needed sometimes when a refcount might
    have an unconventional release which needs more than
    the refcounted object to process object release-- like in the
    files_struct.f_count conversion patch at __aio_put_req().
    The following patch depends on kref shrinkage patches.
    (which you have already included).

    Please include.

    Thanks,
    Kiran

    Signed-off-by: Ravikiran Thirumalai <kiran@in.ibm.com>

    diff -ruN -X dontdiff2 linux-kref-2.6.7/include/linux/kref.h files_struct-kref-2.6.7/include/linux/kref.h
    --- linux-kref-2.6.7/include/linux/kref.h 2004-07-26 18:53:24.000000000 +0530
    +++ files_struct-kref-2.6.7/include/linux/kref.h 2004-07-26 18:48:43.543549752 +0530
    @@ -26,6 +26,8 @@
    void kref_init(struct kref *kref);
    struct kref *kref_get(struct kref *kref);
    void kref_put(struct kref *kref, void (*release) (struct kref *kref));
    +int kref_read(struct kref *kref);
    +int kref_put_last(struct kref *kref);


    #endif /* _KREF_H_ */
    diff -ruN -X dontdiff2 linux-kref-2.6.7/lib/kref.c files_struct-kref-2.6.7/lib/kref.c
    --- linux-kref-2.6.7/lib/kref.c 2004-07-26 18:53:24.228879096 +0530
    +++ files_struct-kref-2.6.7/lib/kref.c 2004-07-26 19:02:20.782310576 +0530
    @@ -54,6 +54,33 @@
    }
    }

    +/**
    + * kref_read - Return the refcount value.
    + * @kref: object.
    + */
    +int kref_read(struct kref *kref)
    +{
    + return atomic_read(&kref->refcount);
    +}
    +
    +/**
    + * kref_put_last - decrement refcount for object.
    + * @kref: object.
    + *
    + * Decrement the refcount, and if 0 return true.
    + * Returns false otherwise.
    + * Use this only if you cannot use kref_put -- when the
    + * release function of kref_put needs more than just the
    + * refcounted object. Use of kref_put_last when kref_put
    + * can do will be frowned upon.
    + */
    +int kref_put_last(struct kref *kref)
    +{
    + return atomic_dec_and_test(&kref->refcount);
    +}
    +
    EXPORT_SYMBOL(kref_init);
    EXPORT_SYMBOL(kref_get);
    EXPORT_SYMBOL(kref_put);
    +EXPORT_SYMBOL(kref_read);
    +EXPORT_SYMBOL(kref_put_last);
    -
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