Use KERN_ARND syscall for random numbers on NetBSD, same as FreeBSD.

[alarixnia]

This system call is present on all supported NetBSD versions and provides an endless stream of non-blocking random data from the kernel's ChaCha20-based CSPRNG. It doesn't require a file like /dev/urandom to be opened.

The system call is documented here (under kern.arandom):
https://netbsd.gw.com/cgi-bin/man-cgi?sysctl+7+NetBSD-7.0

And defined here:
https://nxr.netbsd.org/xref/src/sys/sys/sysctl.h#273

The semantics are the same as FreeBSD so reading 256 bytes per call is fine.

Similar change for getrandom crate: rust-random/getrandom#115

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @joshtriplett (or someone else) soon.

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[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-04T17:23:58.7372421Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-04T17:23:58.7581797Z ##[command]git config gc.auto 0
2019-11-04T17:23:58.7659002Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-04T17:23:58.7726173Z ##[command]git config --get-all http.proxy
2019-11-04T17:23:58.7881493Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66092/merge:refs/remotes/pull/66092/merge
---
2019-11-04T17:31:07.1728770Z    Compiling panic_unwind v0.0.0 (/checkout/src/libpanic_unwind)
2019-11-04T17:31:09.1484026Z error: multiple `cfg` predicates are specified
2019-11-04T17:31:09.1493089Z    --> src/libstd/sys/unix/rand.rs:146:30
2019-11-04T17:31:09.1493563Z     |
2019-11-04T17:31:09.1493853Z 146 | #[cfg(target_os = "freebsd", target_os = "netbsd")]
2019-11-04T17:31:09.1494211Z 
2019-11-04T17:31:09.1494646Z error[E0428]: the name `imp` is defined multiple times
2019-11-04T17:31:09.1494928Z    --> src/libstd/sys/unix/rand.rs:147:1
2019-11-04T17:31:09.1496078Z     |
2019-11-04T17:31:09.1496078Z     |
2019-11-04T17:31:09.1496437Z 21  | mod imp {
2019-11-04T17:31:09.1496801Z     | ------- previous definition of the module `imp` here
2019-11-04T17:31:09.1497015Z ...
2019-11-04T17:31:09.1497415Z 147 | mod imp {
2019-11-04T17:31:09.1497734Z     | ^^^^^^^ `imp` redefined here
2019-11-04T17:31:09.1498258Z     = note: `imp` must be defined only once in the type namespace of this module
2019-11-04T17:31:09.1498320Z 
2019-11-04T17:31:09.1498320Z 
2019-11-04T17:31:09.1498583Z error[E0425]: cannot find value `CTL_KERN` in crate `libc`
2019-11-04T17:31:09.1499043Z    --> src/libstd/sys/unix/rand.rs:151:26
2019-11-04T17:31:09.1499275Z     |
2019-11-04T17:31:09.1499559Z 151 |         let mib = [libc::CTL_KERN, libc::KERN_ARND];
2019-11-04T17:31:09.1499877Z     |                          ^^^^^^^^ not found in `libc`
2019-11-04T17:31:09.1499951Z 
2019-11-04T17:31:09.1500215Z error[E0425]: cannot find value `KERN_ARND` in crate `libc`
2019-11-04T17:31:09.1500466Z    --> src/libstd/sys/unix/rand.rs:151:42
2019-11-04T17:31:09.1500690Z     |
2019-11-04T17:31:09.1500971Z 151 |         let mib = [libc::CTL_KERN, libc::KERN_ARND];
2019-11-04T17:31:09.1501313Z     |                                          ^^^^^^^^^ not found in `libc`
2019-11-04T17:31:11.2315310Z error[E0308]: mismatched types
2019-11-04T17:31:11.2316639Z    --> src/libstd/sys/unix/rand.rs:158:30
2019-11-04T17:31:11.2317149Z     |
2019-11-04T17:31:11.2317607Z 158 | ...                   ptr::null(), 0)
2019-11-04T17:31:11.2317607Z 158 | ...                   ptr::null(), 0)
2019-11-04T17:31:11.2318195Z     |                       ^^^^^^^^^^^ types differ in mutability
2019-11-04T17:31:11.2318633Z     |
2019-11-04T17:31:11.2319134Z     = note: expected type `*mut libc::c_void`
2019-11-04T17:31:11.2319573Z                found type `*const _`
2019-11-04T17:31:11.3021461Z error: aborting due to 5 previous errors
2019-11-04T17:31:11.3022380Z 
2019-11-04T17:31:11.3022989Z Some errors have detailed explanations: E0308, E0425, E0428.
2019-11-04T17:31:11.3023425Z For more information about an error, try `rustc --explain E0308`.
---
2019-11-04T17:31:11.3518027Z   local time: Mon Nov  4 17:31:11 UTC 2019
2019-11-04T17:31:11.5109221Z   network time: Mon, 04 Nov 2019 17:31:11 GMT
2019-11-04T17:31:11.5116188Z == end clock drift check ==
2019-11-04T17:31:14.3831320Z 
2019-11-04T17:31:14.3941353Z ##[error]Bash exited with code '1'.
2019-11-04T17:31:14.3968050Z ##[section]Starting: Checkout
2019-11-04T17:31:14.3969694Z ==============================================================================
2019-11-04T17:31:14.3969921Z Task         : Get sources
2019-11-04T17:31:14.3969966Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[nagisa]

@bors r+

[bors]

📌 Commit b4f92ea has been approved by nagisa