On Mon, Sep 11, 2023 at 06:38:33PM +0200, mwilck@xxxxxxxx wrote:
> From: Martin Wilck <mwilck@xxxxxxxx>
>
> If we can assume that the bindings array is totally ordered for every
> prefix, which the previous patch guarantees, the search for a free ID can be
> simplified.
>
Reviewed-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> libmultipath/alias.c | 87 ++++++++++----------------------------------
> 1 file changed, 19 insertions(+), 68 deletions(-)
>
> diff --git a/libmultipath/alias.c b/libmultipath/alias.c
> index af6565b..66e34e3 100644
> --- a/libmultipath/alias.c
> +++ b/libmultipath/alias.c
> @@ -356,83 +356,34 @@ int get_free_id(const Bindings *bindings, const char *prefix, const char *map_ww
> {
> const struct binding *bdg;
> int i, id = 1;
> - int biggest_id = 1;
> - int smallest_bigger_id = INT_MAX;
>
> vector_foreach_slot(bindings, bdg, i) {
> int curr_id = scan_devname(bdg->alias, prefix);
>
> - /*
> - * Find an unused index - explanation of the algorithm
> - *
> - * ID: 1 = mpatha, 2 = mpathb, ...
> - *
> - * We assume the bindings are unsorted. The only constraint
> - * is that no ID occurs more than once. IDs that occur in the
> - * bindings are called "used".
> - *
> - * We call the list 1,2,3,..., exactly in this order, the list
> - * of "expected" IDs. The variable "id" always holds the next
> - * "expected" ID, IOW the last "expected" ID encountered plus 1.
> - * Thus all IDs below "id" are known to be used. However, at the
> - * end of the loop, the value of "id" isn't necessarily unused.
> - *
> - * "smallest_bigger_id" is the smallest used ID that was
> - * encountered while it was larger than the next "expected" ID
> - * at that iteration. Let X be some used ID. If all IDs below X
> - * are used and encountered in the right sequence before X, "id"
> - * will be > X when the loop ends. Otherwise, X was encountered
> - * "out of order", the condition (X > id) holds when X is
> - * encountered, and "smallest_bigger_id" will be set to X; i.e.
> - * it will be less or equal than X when the loop ends.
> - *
> - * At the end of the loop, (id < smallest_bigger_id) means that
> - * the value of "id" had been encountered neither in order nor
> - * out of order, and is thus unused. (id >= smallest_bigger_id)
> - * means that "id"'s value is in use. In this case, we play safe
> - * and use "biggest_id + 1" as the next value to try.
> - *
> - * biggest_id is always > smallest_bigger_id, except in the
> - * "perfectly ordered" case.
> - */
> - if (curr_id == id) {
> - if (id < INT_MAX)
> - id++;
> - else {
> - id = -1;
> - break;
> - }
> + if (curr_id == -1)
> + continue;
> + if (id > curr_id) {
> + condlog(0, "%s: ERROR: bindings are not sorted", __func__);
> + return -1;
> }
> - if (curr_id > biggest_id)
> - biggest_id = curr_id;
> -
> - if (curr_id > id && curr_id < smallest_bigger_id)
> - smallest_bigger_id = curr_id;
> - }
> -
> - if (id >= smallest_bigger_id)
> - id = biggest_id < INT_MAX ? biggest_id + 1 : -1;
> -
> - if (id > 0) {
> - while(id_already_taken(id, prefix, map_wwid)) {
> - if (id == INT_MAX) {
> - id = -1;
> - break;
> - }
> + while (id < curr_id && id_already_taken(id, prefix, map_wwid))
> id++;
> - if (id == smallest_bigger_id) {
> - if (biggest_id == INT_MAX) {
> - id = -1;
> - break;
> - }
> - if (biggest_id >= smallest_bigger_id)
> - id = biggest_id + 1;
> - }
> - }
> + if (id < curr_id)
> + return id;
> + id++;
> + if (id <= 0)
> + break;
> }
>
> - if (id < 0)
> + for (; id > 0; id++) {
> + if (!id_already_taken(id, prefix, map_wwid))
> + break;
> + }
> +
> + if (id <= 0) {
> + id = -1;
> condlog(0, "no more available user_friendly_names");
> + }
> return id;
> }
>
> --
> 2.42.0
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