On Tue, May 30, 2017 at 9:39 AM, Chandan Rajendra
<chandan@xxxxxxxxxxxxxxxxxx> wrote:
> ovl_dir_read_merged() has the following loop,
>
> for (idx = 0; idx != -1; idx = next) {
> next = ovl_path_next(idx, dentry, &realpath);
>
> if (next != -1) {
> err = ovl_dir_read(&realpath, &rdd);
> if (err)
> break;
> } else {
> /*
> * Insert lowest layer entries before upper ones, this
> * allows offsets to be reasonably constant
> */
> list_add(&rdd.middle, rdd.list);
> rdd.is_lowest = true;
> err = ovl_dir_read(&realpath, &rdd);
> list_del(&rdd.middle);
> }
> }
>
>
> rdd.middle is populated inside ovl_fill_lowest() which is indirectly invoked
> by the call to ovl_dir_read() inside the "else" part of the above "if"
> condition. Before this invocation of ovl_dir_read(), rdd.middle would
> basically be an empty list. So this would mean that the call
> list_add(&rdd.middle, rdd.list) is unnecessary.
>
> Please let me know if I am missing something here.
>
You are missing the fact that rdd.middle is not a new list.
its a list element inserted into the circular list rdd.list as a marker
to the head of the non-lowest entries list.
When referencing &rdd.middle inside ovl_fill_lowest() code
is referencing the same list that was populated in rdd.list,
but with a different head/tail.
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