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    Subject[PATCH V2 1/3] kernel.h: Add DO_ONCE statement expression macro
    Date
    Add a DO_ONCE statement expression analogous to printk_once
    that executes any arbitrary statement exactly once.

    This will take the place of printk_once so that
    DO_ONCE(pr_<foo>) can be more easily written.

    Signed-off-by: Joe Perches <joe@perches.com>
    ---
    include/linux/kernel.h | 11 +++++++++++
    1 files changed, 11 insertions(+), 0 deletions(-)

    diff --git a/include/linux/kernel.h b/include/linux/kernel.h
    index 883cd44..179fdac 100644
    --- a/include/linux/kernel.h
    +++ b/include/linux/kernel.h
    @@ -637,6 +637,17 @@ static inline void ftrace_dump(void) { }
    #define swap(a, b) \
    do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)

    +/*
    + * Do something once (analogous to WARN_ONCE() et al):
    + */
    +#define DO_ONCE(x...) ({ \
    + static unsigned long __done; \
    + \
    + if (!test_and_set_bit(0, &__done)) { \
    + x; \
    + } \
    +})
    +
    /**
    * container_of - cast a member of a structure out to the containing structure
    * @ptr: the pointer to the member.
    --
    1.6.3.1.10.g659a0.dirty


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