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    Subject[PATCH -mm] simplify pid iterators
    On top of Eric's recent include/linux/pid.h changes.

    I think it is hardly possible to read the current do_each_task_pid().
    The new version is much simpler and makes the code smaller.

    Only the do_each_task_pid change is tested, the do_each_pid_task isn't.
    Eric, could you take a hard look at this patch?

    Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

    --- 2.6.18-rc3/include/linux/pid.h~ 2006-08-16 20:40:05.000000000 +0400
    +++ 2.6.18-rc3/include/linux/pid.h 2006-08-18 00:45:06.000000000 +0400
    @@ -99,42 +99,29 @@ static inline pid_t pid_nr(struct pid *p
    return nr;
    }

    -#define pid_next(task, type) \
    - ((task)->pids[(type)].node.next)

    -#define pid_next_task(task, type) \
    - hlist_entry(pid_next(task, type), struct task_struct, \
    - pids[(type)].node)
    -
    -
    -/* We could use hlist_for_each_entry_rcu here but it takes more arguments
    - * than the do_each_task_pid/while_each_task_pid. So we roll our own
    - * to preserve the existing interface.
    - */
    -#define do_each_task_pid(who, type, task) \
    - if ((task = find_task_by_pid_type(type, who))) { \
    - prefetch(pid_next(task, type)); \
    - do {
    -
    -#define while_each_task_pid(who, type, task) \
    - } while (pid_next(task, type) && ({ \
    - task = pid_next_task(task, type); \
    - rcu_dereference(task); \
    - prefetch(pid_next(task, type)); \
    - 1; }) ); \
    - }
    -
    -#define do_each_pid_task(pid, type, task) \
    - if ((task = pid_task(pid, type))) { \
    - prefetch(pid_next(task, type)); \
    - do {
    -
    -#define while_each_pid_task(pid, type, task) \
    - } while (pid_next(task, type) && ({ \
    - task = pid_next_task(task, type); \
    - rcu_dereference(task); \
    - prefetch(pid_next(task, type)); \
    - 1; }) ); \
    - }
    +#define do_each_task_pid(who, type, task) \
    + do { \
    + struct hlist_node *pos___; \
    + struct pid *pid___ = find_pid(who); \
    + if (pid___ != NULL) \
    + hlist_for_each_entry_rcu((task), pos___, \
    + &pid___->tasks[type], pids[type].node) {
    +
    +#define while_each_task_pid(who, type, task) \
    + } \
    + } while (0)
    +
    +
    +#define do_each_pid_task(pid, type, task) \
    + do { \
    + struct hlist_node *pos___; \
    + if (pid != NULL) \
    + hlist_for_each_entry_rcu((task), pos___, \
    + &pid->tasks[type], pids[type].node) {
    +
    +#define while_each_pid_task(pid, type, task) \
    + } \
    + } while (0)

    #endif /* _LINUX_PID_H */
    -
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