58 lines
2.1 KiB
Rust
58 lines
2.1 KiB
Rust
|
use std::io;
|
||
|
|
use std::mem::MaybeUninit;
|
||
|
|
|
||
|
|
pub fn extract_noattr(result: io::Result<Vec<u8>>) -> io::Result<Option<Vec<u8>>> {
|
||
|
|
result.map(Some).or_else(|e| {
|
||
|
|
if e.raw_os_error() == Some(crate::sys::ENOATTR) {
|
||
|
|
Ok(None)
|
||
|
|
} else {
|
||
|
|
Err(e)
|
||
|
|
}
|
||
|
|
})
|
||
|
|
}
|
||
|
|
|
||
|
|
/// Calls `get_value` to with a buffer and `get_size` to estimate the size of the buffer if/when
|
||
|
|
/// `get_value` returns ERANGE.
|
||
|
|
#[allow(dead_code)]
|
||
|
|
pub fn allocate_loop<F, S>(mut get_value: F, mut get_size: S) -> io::Result<Vec<u8>>
|
||
|
|
where
|
||
|
|
F: for<'a> FnMut(&'a mut [MaybeUninit<u8>]) -> io::Result<&'a mut [u8]>,
|
||
|
|
S: FnMut() -> io::Result<usize>,
|
||
|
|
{
|
||
|
|
// Start by assuming the return value is <= 4KiB. If it is, we can do this in one syscall.
|
||
|
|
const INITIAL_BUFFER_SIZE: usize = 4096;
|
||
|
|
match get_value(&mut [MaybeUninit::<u8>::uninit(); INITIAL_BUFFER_SIZE]) {
|
||
|
|
Ok(val) => return Ok(val.to_vec()),
|
||
|
|
Err(e) if e.raw_os_error() != Some(crate::sys::ERANGE) => return Err(e),
|
||
|
|
_ => {}
|
||
|
|
}
|
||
|
|
|
||
|
|
// If that fails, we ask for the size and try again with a buffer of the correct size.
|
||
|
|
let mut vec: Vec<u8> = Vec::new();
|
||
|
|
loop {
|
||
|
|
vec.reserve_exact(get_size()?);
|
||
|
|
match get_value(vec.spare_capacity_mut()) {
|
||
|
|
Ok(initialized) => {
|
||
|
|
unsafe {
|
||
|
|
let len = initialized.len();
|
||
|
|
assert_eq!(
|
||
|
|
initialized.as_ptr(),
|
||
|
|
vec.as_ptr(),
|
||
|
|
"expected the same buffer"
|
||
|
|
);
|
||
|
|
vec.set_len(len);
|
||
|
|
}
|
||
|
|
// Only shrink to fit if we've over-allocated by MORE than one byte. Unfortunately,
|
||
|
|
// on FreeBSD, we have to over-allocate by one byte to determine if we've read all
|
||
|
|
// the attributes.
|
||
|
|
if vec.capacity() > vec.len() + 1 {
|
||
|
|
vec.shrink_to_fit();
|
||
|
|
}
|
||
|
|
return Ok(vec);
|
||
|
|
}
|
||
|
|
Err(e) if e.raw_os_error() != Some(crate::sys::ERANGE) => return Err(e),
|
||
|
|
_ => {} // try again
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|