Shell: Some backgrounding (yes, again) fixes, and some other random fixes #6021
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This is done also by linux (signal.c:936 in v5.11) at least. It's a pretty handy notification that allows the parent process to skip going through a `waitpid` and guesswork to figure out the current state of a child process.
This fixes `fg` and `bg` causing the shell to go into an infinite loop of trying to `waitpid` until some current job changes state. a.k.a. "Fix Shell backgrounding, yet again!" :P
This can happen if the process is stopped and continued at a later time.
This makes commands like `foo 2>&1 | bar` behave as expected (which is to pipe both stdout and stderr of `foo` to stdin of `bar`). Previously, this would've piped stderr of `foo` into stdout, and the stdout of `foo` into the stdin of `bar`.
Otherwise it'll have some random value from the stack, and the kernel will not bother setting it to zero. Also add a debug print and tweak the FIXME message.
alimpfard
changed the title
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#if *_DEBUGA "PROMPT" function, to maybe try and move away from cryptic yet-more-escapes approachThe last one is too slow to be usable, so this PR is gonna remain a draft for now, I'll split the unrelated fixes if it takes too long.
Profiling 10 iterations of running
PROMPTsays that about 60% of the runtime is spent in syscalls, with about half of that being justfork()andmmap().For reference, running the same
PROMPTfunction in linux (withLagom/shell) takes about 10ms, so there's quite a big room for improvement.Any clues about why
fork()is taking so long (and how to fix it) would be much appreciated, since I'm a complete and total n00b at dealing with this sort of thing.-> #6043