[vidarh]

It uses a 32K buffer, sure (at least that's what strace shows me on my machine; EDIT: glibc dynamically chooses buffer size in opendir() based on reported st_blksize, up to 1MB)

But I've run ls on systems with several orders of magnitude slower drives than what we're used to today, and it really isn't generally what causes people to complain of ls being slow on large directories in practice.

Even with ext2fs which was notoriously bad at handling large directories, exported via NFS filesystems over 10Mbs ethernet backed by 90's era IDE drives, the buffer size was rarely enough of a problem to matter once you turned off the sorting.

(To be clear, I'm not saying it won't ever make a difference; but in practice, over decades of running into this complaint, it's just not been the issue - most of the time peoples problem is interactive use where they run into having to wait for ls to read the whole dir to start getting results, not total throughput)

[saddlerustle]

I mean, I only say this bc I wrote a tool like OP's back in the day and got a ~5x speedup over `ls -f` in a particular environment, but sure YMMV.

[vidarh]

I edited my comment. Current glibc will dynamically choose buffer sizes up to 1MB of dirent structures depending on reported st_blksize. No idea when it started doing that, so it might well be it does better now.

I'm sure there are circumstances where a 5x speedup will matter, but most of the time where people use "ls" it's interactively on the command line and it's just not been my experience that it matters in the circumstances where I've had to help people with this. It's more of a "we're right in the middle of something and can't get any results back" kind of situation. I'd say 9 out of 10 times I've had people bring up an issue like this it's because they're uncomfortable with "find" and are trying to get a list of files to do something with that they could easily do directly with "find" and/or where "ls -f" is more than sufficient.

But as you say, YMMV.

[fragmede]

It used to be a fixed 4k buffer. Later versions of ls (coreutils) raised that, and made it dynamic.