bug#70586: cp walks dir differently than rm and is hitting "File name too long" where this could be avoided

On 2025-10-19 19:18, Collin Funk wrote:

>       $ ulimit -n
>       1024
> 
> It is easy to hit this limit even if you only open file descriptors to
> the parents of the file that you want to copy.

(I assume by "parents" you mean "ancestors".)

Yes, and that's why Gnulib fts doesn't do that.


>     int
>     open_deep (char const *filename, int flags, ...)
>     {
...>       /* Loop through the patch components using openat on each
>          until we open FILENAME.  */
>       return result;

That's O(N * D) if you open N files nested D deep, which is not a good 
thing. We should be able to do O(N + D).


> is there a reason why savewd and
> mkancesdirs don't use openat + mkdirat instead of using chdir in a child
> process? Do these functions just predate the *at interfaces

Yes, precisely. Some day it will be time to give up on those old 
platforms, I suppose. We haven't done that yet because there hasn't been 
motivation to get rid of them, or rewrite them.