2.4.0test - uid_hash_find()

From: Dan Aloni (karrde@callisto.yi.org)
Date: Sun Oct 08 2000 - 18:10:55 EDT

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    I've been touring around the kernel sources when I stumbled
    across the uid_hash_find() function (kernel/user.c):

    static inline struct user_struct *uid_hash_find(unsigned short uid, unsigned int hashent)
    {
            struct user_struct *up, *next;
     
            next = uidhash[hashent];
            for (;;) {
                    up = next;
                    if (next) {
                            next = up->next;
                            if (up->uid != uid)
                                    continue;
                            atomic_inc(&up->__count);
                     }
                    break;
            }
            return up;
    }

    Now, it took me some time to figure out how this function
    behaves, and I came into conclusion that the implementation
    is not only an unreadable piece of code, but also inefficient.

    Give one reason why we shouldn't use this:

    static inline struct user_struct *uid_hash_find(unsigned short uid, unsigned int hashent)
    {
            struct user_struct *up;
     
            for (up = uidhash[hashent]; up ; up = up->next)
                    if (up->uid == uid)
                    {
                            atomic_inc(&up->__count);
                            return up;
                     }

            return NULL;
    }

    [compiled, booted, and it works fine]

    The patch:

    --- linux/kernel/user.c Sun Aug 13 16:36:42 2000
    +++ linux.vanilla/kernel/user.c Sun Oct 8 19:34:07 2000
    @@ -53,20 +53,16 @@
     
     static inline struct user_struct *uid_hash_find(unsigned short uid, unsigned int hashent)
     {
    - struct user_struct *up, *next;
    + struct user_struct *up;
     
    - next = uidhash[hashent];
    - for (;;) {
    - up = next;
    - if (next) {
    - next = up->next;
    - if (up->uid != uid)
    - continue;
    - atomic_inc(&up->__count);
    + for (up = uidhash[hashent]; up ; up = up->next)
    + if (up->uid == uid)
    + {
    + atomic_inc(&up->__count);
    + return up;
                     }
    - break;
    - }
    - return up;
    +
    + return NULL;
     }
     
     /* 

    -- 
Dan Aloni 
dax@karrde.org

    -
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