Make cache private for each mount and enforce LRU eviction.

[rslota]

No description provided.

[rslota]

Reviews in this chain:
└#3 Make cache private for each mount and enforce LRU eviction.

[rslota]

#	head	base	diff	date	summary
0	64ee52f3	a9bc569b	diff	Feb 25 18:48 PM	8 files changed, 746 insertions(+), 63 deletions(-)
1	3b1aca2e	a9bc569b	diff	Feb 26 15:08 PM	3 files changed, 9 insertions(+), 3 deletions(-)

[erszcz]

We'd probably want to use async at this point (possibly Tokio, since it's the most popular, or some other runtime if there's some merit behind a particular one), but that's definitely out of scope of this PR

[rslota]

This is just moved, I didn't add this in this PR. I think that would be bigger rewrite 🤷

[erszcz]

Not that I've known it myself, but seems legit:

kill(pid, 0) returns -1 with errno == EPERM if the process exists but belongs to another user. The current check would treat that as "dead" and delete the directory. Should check errno != ESRCH instead:

fn is_process_alive(pid: u32) -> bool {
    let ret = unsafe { libc::kill(pid as i32, 0) };
    if ret == 0 {
        return true;
    }
    // EPERM means process exists but we lack permission to signal it
    std::io::Error::last_os_error().raw_os_error() != Some(libc::ESRCH)
}

[rslota]

fair, I mostly ignored this because in our cases that can never happen, but fine 🤷

[erszcz]

LGTM in general, but might be worth checking the is_process_alive details