Fix EOF (^D) handling in devpts (partially addr #9333)

[thundergolfer]

This fixes the ctrl-d part of #9333.

Disclaimer: new to this codebase.

[nlacasse]

Thanks for the fix, and the nice test. One minor nit.

[ayushr2]

Could you squash the two commits? Otherwise these will appear as two separate commits on the master branch after merge.

[thundergolfer]

Oh sure, I thought I could squash just before merge. But I'll squash them now and force push.

[ayushr2]

We don't squash and merge from Github UI (unfortunately...). It needs be go through our internal system (via the "ready to pull" tag). Copybara will clone your PR as a new PR and merge that and close this. And in the process, it just pushes the commits from this branch onto master. So we request the commits are squashed (unless they are meant to be logically separated).

[thundergolfer]

Make sense. Thanks for the explanation 👌

[nlacasse]

This seems to break the PtyTest.TermiosONLCR test:

[ RUN      ] PtyTest.TermiosONLCR
test/syscalls/linux/pty.cc:466: Failure
Value of: ReadFd(fd.get(), &c, 1)
Expected: -1 (failure), with errno PosixError(errno=11 Resource temporarily unavailable)
  Actual: 0 (of type long)
[  FAILED  ] PtyTest.TermiosONLCR (5 ms)

Full logs here

[thundergolfer]

Oh of course, this behavior is only valid in canonical mode, and that test disables the ICANON flag. Pushed a fix.

Edit: commit now passes make test TARGETS=//test/syscalls:pty_test_runsc_ptrace_shared

[nlacasse]

We have to hold l.termiosMu to access l.termios.

I would set isCanon := l.termios.LEnabled(linux.ICANON) while the lock is held on line 200, and then reference isCanon in this conditional.

[nlacasse]

This is merged! Thanks for the PR.