Add epollerr support

[tiif]

Fixes #3816

For socketpair, if the peer fd is closed while having data in its read buffer, EPOLLER will be thrown.

This is still WIP because I am currently finding a way to check if peer fd still has something in its readbuf when it is closed and add the EPOLLER flag In get_epoll_ready_events.

[RalfJung]

For socketpair, if the peer fd is closed while having data in its read buffer, EPOLLER will be thrown.

Ah, very interesting. If the peer FD is closed without any data in its read buffer, all is fine, but if there is data being discarded, that's not fine? I guess I can see how it makes sense, but it'd be better if we'd find documentation explaining this...

First sketch of an implementation:

• add a new field to SocketPair: peer_lost_data: Cell<bool>, initially false
• in close, if our own read buffer is non-empty and we still have a peer, set the peer's peer_lost_data flag to true
• in get_epoll_ready_events, if peer_lost_data is true, set EPOLLERR

Does EPOLERR ever get unset again after this?

[tiif]

If the peer FD is closed without any data in its read buffer, all is fine, but if there is data being discarded, that's not fine?

Yes. If the peer FD read all its data before it get closed, EPOLLER won't be triggered.

Does EPOLERR ever get unset again after this?

In the context of the current test case we have in this PR, I think EPOLLER can only be triggered once because we only can close the peer_fd for once.

@rustbot author

[tiif]

@rustbot ready

[RalfJung]

Looks good, thanks :)
@bors r+

[bors]

📌 Commit 81c02da has been approved by RalfJung

It is now in the queue for this repository.

[bors]

☔ The latest upstream changes (presumably #3824) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

1. git checkout epoller (switch to your branch)
2. git fetch upstream master (retrieve the latest master)
3. git rebase upstream/master -p (rebase on top of it)
4. Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
5. git push self epoller --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Auto-merging tests/pass-dep/libc/libc-epoll.rs
CONFLICT (content): Merge conflict in tests/pass-dep/libc/libc-epoll.rs
Auto-merging src/shims/unix/linux/epoll.rs
Automatic merge failed; fix conflicts and then commit the result.

[RalfJung]

@rustbot author

[tiif]

Maybe it will conflict again after #3818 landed, I will come back later to check.

EDIT: oh that haven't landed

[RalfJung]

We'll see. :)
@bors r+

[bors]

📌 Commit 7ca2aa5 has been approved by RalfJung

It is now in the queue for this repository.

[RalfJung]

Ah yes they both add tests to the end of the same file so they will definitely conflict there.

[bors]

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

1. git checkout epoller (switch to your branch)
2. git fetch upstream master (retrieve the latest master)
3. git rebase upstream/master -p (rebase on top of it)
4. Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
5. git push self epoller --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Auto-merging tests/pass-dep/libc/libc-epoll.rs
CONFLICT (content): Merge conflict in tests/pass-dep/libc/libc-epoll.rs
Auto-merging src/shims/unix/linux/epoll.rs
Automatic merge failed; fix conflicts and then commit the result.

[tiif]

@RalfJung Alright, last one. Thanks for being fast in reviewing this stream of PRs. :)

[RalfJung]

Thanks for being fast in reacting to feedback and conflicts. :)
@bors r+

[bors]

📌 Commit 6e76ba3 has been approved by RalfJung

It is now in the queue for this repository.

[bors]

⌛ Testing commit 6e76ba3 with merge 0665f6e...

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing 0665f6e to master...

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing 0665f6e to master...