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Mechanism to query existing signal handler #2172

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cpick opened this issue Oct 20, 2023 · 2 comments · May be fixed by #2190
Open

Mechanism to query existing signal handler #2172

cpick opened this issue Oct 20, 2023 · 2 comments · May be fixed by #2190

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@cpick
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cpick commented Oct 20, 2023

If NULL is passed as the second (new action) argument to sigaction(), then it won't make any changes, but will return the existing action.

I don't believe nix provides any way to access this behavior. The type of nix::sys::signal::sigaction()s sigaction argument could be changed from &SigAction to Option<&SigAction>, but this would be a breaking change and also would mean doing a read-only query of the current action would only be possible with an unsafe function call.

I'd prefer something like a safe sigaction_get() (roughly akin to this proposal for a sigaction_safe()).
@asomers
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asomers commented Nov 11, 2023

Could you suggest a complete API, or better yet post a PR?

cpick pushed a commit to cpick/nix that referenced this issue Nov 14, 2023
Add signal::sigaction_current()
0ddb10c 
Provide a way to query the currently installed sigaction.

The decision to add `sigaction_current()` instead of just exposing the
`sigaction_inner()` function was to avoid any confusion over the
semantics of passing in a `None` `sigaction` argument (eg: someone
thinking that it meant remove or reset the action).

This builds towards nix-rust#2172.
cpick pushed a commit to cpick/nix that referenced this issue Nov 14, 2023
Add signal::sigaction_current()
30a6eee 
Provide a way to query the currently installed sigaction.

The decision to add `sigaction_current()` instead of just exposing the
`sigaction_inner()` function was to avoid any confusion over the
semantics of passing in a `None` `sigaction` argument (eg: someone
thinking that it meant remove or reset the action).

This builds towards nix-rust#2172.
cpick pushed a commit to cpick/nix that referenced this issue Nov 14, 2023
Add signal::sigaction_is_{default,ignore}()
0e88e0e 
Provide safe mechanisms to determine whether a signal's action is the
default or ignore.
This covers the majority of real-world calls to `sigaction()` with a
NULL action without needing any unsafe code.

Fixes nix-rust#2172.
@cpick cpick linked a pull request Nov 14, 2023 that will close this issue
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@cpick
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cpick commented Nov 14, 2023

Could you suggest a complete API, or better yet post a PR?

Sure thing.

I've opened #2190 with my suggested implementation.

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Added sigaction_is_default(), sigaction_is_ignore(), and sigaction_current() functions cpick/nix
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@asomers @cpick