zlacker

I’m assuming you are proposing to stat each candidate before trying to execve it. I’m also assuming that a stat system call is roughly as expensive as an execve of a nonexistent or non-executable path.

For every failed candidate, you are doing one system call, so roughly the same cost each way.

Now if you just do an execve, you’re just paying that cost. If you stat first, you pay the cost of another system call that doesn’t change the flow of your program at all (a nice way of saying you’re wasting time).

Unless stat is dramatically faster than exec on a nonexistent or non-executable path, there’s never a case where this is better.

>>koenig+(OP)
Context switches could straightforwardly be saved by doing the PATH splitting and lookup in-kernel, or just providing a list of executable paths to check.

It didn't work out this way historically (doing unnecessary string processing, requiring extra memory, could've been more expensive than the context switches), and the performance impact of failed execve isn't normally a high priority, and there are other reasons not to want stuff in the kernel (not that it stops frankly less critical stuff from getting in the kernel), but there's definitely low-hanging fruit here if it like, mattered.