sys: add map_ids to bpf_prog_get_info_by_fd #747
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Allows the caller to pass a slice which the kernel will populate with map ids used by the program.
| let mut attr = unsafe { mem::zeroed::<bpf_attr>() }; | ||
| // info gets entirely populated by the kernel | ||
| let info = MaybeUninit::zeroed(); | ||
| let mut info = unsafe { mem::zeroed() }; |
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Can this stay as MaybeUninit::zeroed(); ?
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How's that better? We'll need to immediately assume_init so we can write to it.
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why not just call as_mut_ptr() on info in the init closure? Since we only need to assume_init in that one case
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We'd still need to assume_init later, before returning. What is the benefit of using MaybeUninit here?
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Or just use as_mut_ptr() here and ONLY do unsafe code in that one case
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This doesn't make sense - look at the diff. Before the change, we had unsafe code on the return path.
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Writing through MaybeUninit::as_mut_ptr is nasty:
Gets a mutable pointer to the contained value. Reading from this pointer or turning it into a reference is undefined behavior unless the MaybeUninit is initialized.
https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_mut_ptr
That means we can't turn it into a mutable reference because that's UB. Again, how is this better?
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Fair enough I guess there is no way to protect against the unsafe code here 👍 In the docs it says
This has the same effect as [MaybeUninit::zeroed().assume_init()](https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.zeroed). It is useful for FFI sometimes, but should generally be avoided.
This is the "useful for FFI case" lol :)
Allows the caller to pass a slice which the kernel will populate with
map ids used by the program.