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getgroups: Reuse buffer, add comment about performance

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This commit is contained in:
Jan Verbeek 2021-09-13 16:15:03 +02:00
parent b125159535
commit ceff2690d2
1 changed files with 4 additions and 1 deletions
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5
src/uucore/src/lib/features/entries.rs
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@ -72,6 +72,7 @@ extern "C" {
/// > to be used in a further call to getgroups(). /// > to be used in a further call to getgroups().
#[cfg(not(target_os = "redox"))] #[cfg(not(target_os = "redox"))]
pub fn get_groups() -> IOResult<Vec<gid_t>> { pub fn get_groups() -> IOResult<Vec<gid_t>> {
let mut groups = Vec::new();
loop { loop {
let ngroups = match unsafe { getgroups(0, ptr::null_mut()) } { let ngroups = match unsafe { getgroups(0, ptr::null_mut()) } {
-1 => return Err(IOError::last_os_error()), -1 => return Err(IOError::last_os_error()),
@ -80,7 +81,9 @@ pub fn get_groups() -> IOResult<Vec<gid_t>> {
n => n, n => n,
}; };
let mut groups = vec![0; ngroups.try_into().unwrap()]; // This is a small buffer, so we can afford to zero-initialize it and
// use safe Vec operations
groups.resize(ngroups.try_into().unwrap(), 0);
let res = unsafe { getgroups(ngroups, groups.as_mut_ptr()) }; let res = unsafe { getgroups(ngroups, groups.as_mut_ptr()) };
if res == -1 { if res == -1 {
let err = IOError::last_os_error(); let err = IOError::last_os_error();