Error when there is an unsupported flag for opening a file

[pvdrz]

@RalfJung this is my attempt to check for undesired flags. I also changed fcntl to error when doing any other action besides getting the flags for a fd

[bors]

☔ The latest upstream changes (presumably #983) made this pull request unmergeable. Please resolve the merge conflicts.

[RalfJung]

Hm... now the odd part is that CI works here, isn't it? When you do File::open(path), shouldn't this return something from F_GETFD that does not have FD_CLOEXEC set, and thus lead to an F_SETFD call and hence an error?

[RalfJung]

(Also #973 still has some unresolved comments, not sure if you wanted to do separate PRs or add them here.)

[pvdrz]

Hm... now the odd part is that CI works here, isn't it? When you do File::open(path), shouldn't this return something from F_GETFD that does not have FD_CLOEXEC set, and thus lead to an F_SETFD call and hence an error?

Hmm yeah, that's odd. Maybe it happens because some of the O_* flags overlap with the FD_* flags and the bits for FD_CLOEXEC are set by pure luck. In that case I think I'll remove the flag field from the FIleHandle and return just FD_CLOEXEC given that this is always set by std.

Quote from man:

The following commands manipulate the flags associated with a file
descriptor. Currently, only one such flag is defined: FD_CLOEXEC,
the close-on-exec flag.

So it is ok to just return FD_CLOEXEC but I'll add some comments for this.

EDIT: Should I just remove the FileHandle type completely?

[pvdrz]

(Also #973 still has some unresolved comments, not sure if you wanted to do separate PRs or add them here.)

I think I won't be adding more changes to this PR. I'll take care of those comments after the changes to make public the memory field are merged.

[RalfJung]

Thanks a lot! @bors r+

As a follow-up, one thing that would be nice to do is add some tests that trigger BADFD to catch errors like this one.

[bors]

📌 Commit 2487223 has been approved by RalfJung

[bors]

⌛ Testing commit 2487223 with merge 49cab51...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: RalfJung
Pushing 49cab51 to master...