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    SubjectRe: [PATCH v3 01/17] hashtable: introduce a small and naive hashtable
    On Thu, Sep 06, 2012 at 03:53:58PM +0200, Sasha Levin wrote:
    > On 09/04/2012 07:01 PM, Mathieu Desnoyers wrote:
    > >> #define do_for_each_ftrace_rec(pg, rec) \
    > >> > for (pg = ftrace_pages_start, rec = &pg->records[pg->index]; \
    > >> > pg && rec == &pg->records[pg->index]; \
    > >> > pg = pg->next) \
    > >> > for (rec = pg->records; rec < &pg->records[pg->index]; rec++)
    > > Maybe in some cases there might be ways to combine the two loops into
    > > one ? I'm not seeing exactly how to do it for this one, but it should
    > > not be impossible. If the inner loop condition can be moved to the outer
    > > loop, and if we use (blah ? loop1_conf : loop2_cond) to test for
    > > different conditions depending on the context, and do the same for the
    > > 3rd argument of the for() loop. The details elude me for now though, so
    > > maybe it's complete non-sense ;)
    > >
    > > It might not be that useful for do_for_each_ftrace_rec, but if we can do
    > > it for the hash table iterator, it might be worth it.
    >
    > So I think that for the hash iterator it might actually be simpler.
    >
    > My solution to making 'break' work in the iterator is:
    >
    > for (bkt = 0, node = NULL; bkt < HASH_SIZE(name) && node == NULL; bkt++)
    > hlist_for_each_entry(obj, node, &name[bkt], member)
    >
    > We initialize our node loop cursor with NULL in the external loop, and the
    > external loop will have a new condition to loop while that cursor is NULL.
    >
    > My logic is that we can only 'break' when we are iterating over an object in the
    > internal loop. If we're iterating over an object in that loop then 'node != NULL'.
    >
    > This way, if we broke from within the internal loop, the external loop will see
    > node as not NULL, and so it will stop looping itself. On the other hand, if the
    > internal loop has actually ended, then node will be NULL, and the outer loop
    > will keep running.
    >
    > Is there anything I've missed?

    Looks reasonable. However, it would break (or rather, not break) on
    code like this:

    hash_for_each_entry(...) {
    if (...) {
    foo(node);
    node = NULL;
    break;
    }
    }

    Hiding the double loop still seems error-prone.

    - Josh Triplett


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