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I have no idea why I didn't do this right from the start, it makes
this whole thing much easier.
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i have been planning to implement something like this for a while now.
it should be faster when doing consecutive syscalls (to be tested).
it will also be helpful in writing the elf loader
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holy shit.
this was simpler than i expected it to be
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I started implementing native semaphores in the kernel, but then I've
realized that I can implement them in userland using pipes.
Thus, this hot garbage was born.
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Without separate read/write ends you can't tell when there are no more writers left if you have multiple readers. Consider this piece of code:
int fd = pipe();
fork(); // execution continues in 2 processes
while (read(fd, &some_buf, sizeof somebuf) >= 0) {
...
}
Once both processes call `read()`, it's obvious that no writes are possible - all the processes that hold a reference to the pipe are currently stuck on a `read()` call, so the kernel could just make it return an error in both. But, what then? It's still possible to write to the pipe, and you can't know if the other process will do that. Thus, if you don't want to miss any output, you have to keep reading the pipe. Forever. Both processes end up stuck.
Having separate read/write ends prevents that.
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