pub unsafe fn dup2_raw<Fd1: AsFd, Fd2: IntoRawFd>(
oldfd: Fd1,
newfd: Fd2,
) -> Result<OwnedFd>Expand description
Create a copy of oldfd with any fd value you want.
§Safety
Since this function returns an OwnedFd, you have to ensure that the returned
OwnedFd is the ONLY owner of the file descriptor specified newfd. Otherwise,
double close could happen.
let oldfd: OwnedFd = open("foo", OFlag::O_RDONLY, Mode::empty()).unwrap();
let newfd: OwnedFd = open("bar", OFlag::O_RDONLY, Mode::empty()).unwrap();
// SAFETY:
// it is NOT safe.
// NOTE that we are passing a RawFd to `newfd`
let duplicated_fd: OwnedFd = unsafe { dup2_raw(&oldfd, newfd.as_raw_fd()) }.unwrap();
// `newfd` and `duplicated_fd` refer to the same file descriptor, and
// they are both owned, double close will happen here.§Examples
Duplicate a file descriptor with a descriptor that is still not open:
let oldfd = open("foo", OFlag::O_RDONLY, Mode::empty()).unwrap();
// SAFETY:
// It is safe given that we are sure that fd 100 is not open, and the returned
// OwnedFd will be its only owner.
let duplicated_fd = unsafe { dup2_raw(&oldfd, 100) }.unwrap();
// do something with `duplicated_fd`The code demonstrating double close can be fixed by passing newfd by value:
let oldfd: OwnedFd = open("foo", OFlag::O_RDONLY, Mode::empty()).unwrap();
let newfd: OwnedFd = open("bar", OFlag::O_RDONLY, Mode::empty()).unwrap();
// SAFETY:
// it is safe since `duplicated_fd` is the only owner of the fd it refers to.
// NOTE that we are passing `newfd` by value, i.e., transfer the ownership
let duplicated_fd: OwnedFd = unsafe { dup2_raw(&oldfd, newfd) }.unwrap();