1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140

// Copyright 2019 Developers of the Rand project.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use crate::error::ERRNO_NOT_POSITIVE;
use crate::util::LazyUsize;
use crate::Error;
use core::num::NonZeroU32;
use core::ptr::NonNull;

cfg_if! {
    if #[cfg(any(target_os = "netbsd", target_os = "openbsd", target_os = "android"))] {
        use libc::__errno as errno_location;
    } else if #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "redox"))] {
        use libc::__errno_location as errno_location;
    } else if #[cfg(any(target_os = "solaris", target_os = "illumos"))] {
        use libc::___errno as errno_location;
    } else if #[cfg(any(target_os = "macos", target_os = "freebsd", target_os = "dragonfly"))] {
        use libc::__error as errno_location;
    } else if #[cfg(target_os = "haiku")] {
        use libc::_errnop as errno_location;
    }
}

pub fn last_os_error() -> Error {
    let errno = unsafe { *errno_location() };
    if errno > 0 {
        Error::from(NonZeroU32::new(errno as u32).unwrap())
    } else {
        ERRNO_NOT_POSITIVE
    }
}

// Fill a buffer by repeatedly invoking a system call. The `sys_fill` function:
//   - should return -1 and set errno on failure
//   - should return the number of bytes written on success
pub fn sys_fill_exact(
    mut buf: &mut [u8],
    sys_fill: impl Fn(&mut [u8]) -> libc::ssize_t,
) -> Result<(), Error> {
    while !buf.is_empty() {
        let res = sys_fill(buf);
        if res < 0 {
            let err = last_os_error();
            // We should try again if the call was interrupted.
            if err.raw_os_error() != Some(libc::EINTR) {
                return Err(err);
            }
        } else {
            // We don't check for EOF (ret = 0) as the data we are reading
            // should be an infinite stream of random bytes.
            buf = &mut buf[(res as usize)..];
        }
    }
    Ok(())
}

// A "weak" binding to a C function that may or may not be present at runtime.
// Used for supporting newer OS features while still building on older systems.
// F must be a function pointer of type `unsafe extern "C" fn`. Based off of the
// weak! macro in libstd.
pub struct Weak {
    name: &'static str,
    addr: LazyUsize,
}

impl Weak {
    // Construct a binding to a C function with a given name. This function is
    // unsafe because `name` _must_ be null terminated.
    pub const unsafe fn new(name: &'static str) -> Self {
        Self {
            name,
            addr: LazyUsize::new(),
        }
    }

    // Return a function pointer if present at runtime. Otherwise, return null.
    pub fn ptr(&self) -> Option<NonNull<libc::c_void>> {
        let addr = self.addr.unsync_init(|| unsafe {
            libc::dlsym(libc::RTLD_DEFAULT, self.name.as_ptr() as *const _) as usize
        });
        NonNull::new(addr as *mut _)
    }
}

pub struct LazyFd(LazyUsize);

impl LazyFd {
    pub const fn new() -> Self {
        Self(LazyUsize::new())
    }

    // If init() returns Some(x), x should be nonnegative.
    pub fn init(&self, init: impl FnOnce() -> Option<libc::c_int>) -> Option<libc::c_int> {
        let fd = self.0.sync_init(
            || match init() {
                // OK as val >= 0 and val <= c_int::MAX < usize::MAX
                Some(val) => val as usize,
                None => LazyUsize::UNINIT,
            },
            || unsafe {
                // We are usually waiting on an open(2) syscall to complete,
                // which typically takes < 10us if the file is a device.
                // However, we might end up waiting much longer if the entropy
                // pool isn't initialized, but even in that case, this loop will
                // consume a negligible amount of CPU on most platforms.
                libc::usleep(10);
            },
        );
        match fd {
            LazyUsize::UNINIT => None,
            val => Some(val as libc::c_int),
        }
    }
}

cfg_if! {
    if #[cfg(any(target_os = "linux", target_os = "emscripten"))] {
        use libc::open64 as open;
    } else {
        use libc::open;
    }
}

// SAFETY: path must be null terminated, FD must be manually closed.
pub unsafe fn open_readonly(path: &str) -> Option<libc::c_int> {
    debug_assert!(path.as_bytes().last() == Some(&0));
    let fd = open(path.as_ptr() as *mut _, libc::O_RDONLY | libc::O_CLOEXEC);
    if fd < 0 {
        return None;
    }
    // O_CLOEXEC works on all Unix targets except for older Linux kernels (pre
    // 2.6.23), so we also use an ioctl to make sure FD_CLOEXEC is set.
    #[cfg(target_os = "linux")]
    libc::ioctl(fd, libc::FIOCLEX);
    Some(fd)
}