Struct Fd 

pub struct Fd(/* private fields */);

An owned file descriptor that closes on drop.

Fd is move-only. Constructing one from a raw descriptor transfers close ownership to Fd; do not also close the raw descriptor elsewhere.

Fork Safety

Fd instances created by Core usually have O_CLOEXEC set. If the process forks, the descriptor will be inherited by the child but will be closed automatically upon exec. Callers that need a descriptor to survive exec must clear the flag manually.

Implementations

impl Fd

pub unsafe fn from_owned_raw_fd( fd: RawFd, op: &'static str, ) -> Result<Self, CoreError>

Wrap an owned raw file descriptor.

Safety

The caller must guarantee fd is valid, open, and uniquely owned by the returned Fd. Passing a borrowed fd, or closing fd after this call, can cause double-close or use-after-close bugs.

pub fn eventfd(init: u32) -> Result<Self, CoreError>

Create a non-blocking eventfd with EFD_CLOEXEC.

The descriptor is created with FD_CLOEXEC set.

Errors

• EINVAL: init is invalid.
• EMFILE: Process limit on open file descriptors hit.
• ENFILE: System-wide limit on open files hit.

pub fn timerfd() -> Result<Self, CoreError>

Create a non-blocking timerfd using CLOCK_MONOTONIC with TFD_CLOEXEC.

The descriptor is created with FD_CLOEXEC set.

Errors

• EMFILE: Process limit on open file descriptors hit.
• ENFILE: System-wide limit on open files hit.
• ENOMEM: Insufficient kernel memory.

pub fn dup2(&self, target: RawFd) -> Result<(), CoreError>

Perform a dup2 syscall.

Errors

• EBADF: The source or target file descriptor is invalid.
• EMFILE: The target descriptor exceeds the process limit.

pub fn set_nonblock(&self) -> Result<(), CoreError>

Set the O_NONBLOCK flag on the descriptor.

Errors

• EBADF: The file descriptor is invalid.

pub fn set_cloexec(&self) -> Result<(), CoreError>

Set the FD_CLOEXEC flag on the descriptor.

Errors

• EBADF: The file descriptor is invalid.

pub fn read_slice(&self, buf: &mut [u8]) -> Result<Option<usize>, CoreError>

Read bytes into a mutable slice.

Returns Ok(None) if the operation would block (EAGAIN).

Edge Cases

• Zero-length read: Returns Ok(Some(0)) immediately.
• Partial read: Returns the number of bytes actually read.

Errors

• EBADF: The file descriptor is invalid or not open for reading.
• EFAULT: buf points outside the process’s address space.
• EIO: Low-level I/O error.

pub fn seek_set(&self, offset: i64) -> Result<u64, CoreError>

Seek to an absolute file offset.

Errors

• EBADF: The file descriptor is not seekable.
• EINVAL: offset is invalid.
• EOVERFLOW: The resulting offset exceeds the off_t range.

pub fn write_slice(&self, buf: &[u8]) -> Result<Option<usize>, CoreError>

Write bytes from a slice.

Returns Ok(None) if the operation would block (EAGAIN).

Edge Cases

• Zero-length write: Returns Ok(Some(0)) immediately.
• Partial write: Returns the number of bytes actually written.

Errors

• EBADF: The file descriptor is invalid or not open for writing.
• EFAULT: buf points outside the process’s address space.
• EPIPE: The reading end of a pipe or socket was closed.

pub fn read_u64(&self) -> Result<Option<u64>, CoreError>

Read a native-endian u64.

Returns Ok(None) if the operation would block (EAGAIN).

pub fn write_u64(&self, value: u64) -> Result<Option<usize>, CoreError>

Write a native-endian u64.

Returns Ok(None) if the operation would block (EAGAIN).

pub fn set_timer_oneshot( &self, delay: Option<Duration>, ) -> Result<(), CoreError>

Arm or disarm a one-shot timerfd.

Passing None disarms the timer. Zero durations are rounded up to one nanosecond so the timer still expires.

Errors

• EBADF: The file descriptor is invalid.
• EINVAL: The duration is invalid or not supported by the kernel.

Trait Implementations

impl AsRawFd for Fd

fn as_raw_fd(&self) -> RawFd

Extracts the raw file descriptor.

impl Drop for Fd

fn drop(&mut self)

Executes the destructor for this type.

fn pin_drop(self: Pin<&mut Self>)

🔬This is a nightly-only experimental API. (pin_ergonomics)

Execute the destructor for this type, but different to Drop::drop, it requires self to be pinned.