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Document Linux kernel handoff in std::io::copy and std::fs::copy #95294

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merged 2 commits into from
Mar 30, 2022
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Document Linux kernel handoff in std::io::copy and std::fs::copy #95294

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93e9f5e
Document Linux kernel handoff in std::io::copy and std::fs::copy
sourcefrog Mar 25, 2022
cfee2ed
Warn that platform-specific behavior may change
sourcefrog Mar 30, 2022
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12 changes: 9 additions & 3 deletions library/std/src/fs.rs
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Expand Up @@ -1729,11 +1729,17 @@ pub fn rename<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<()>
/// This function currently corresponds to the `open` function in Unix
/// with `O_RDONLY` for `from` and `O_WRONLY`, `O_CREAT`, and `O_TRUNC` for `to`.
/// `O_CLOEXEC` is set for returned file descriptors.
///
/// On Linux (including Android), this function attempts to use `copy_file_range(2)`,
/// and falls back to reading and writing if that is not possible.
///
/// On Windows, this function currently corresponds to `CopyFileEx`. Alternate
/// NTFS streams are copied but only the size of the main stream is returned by
/// this function. On MacOS, this function corresponds to `fclonefileat` and
/// `fcopyfile`.
/// Note that, this [may change in the future][changes].
/// this function.
///
/// On MacOS, this function corresponds to `fclonefileat` and `fcopyfile`.
///
/// Note that platform-specific behavior [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
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10 changes: 10 additions & 0 deletions library/std/src/io/copy.rs
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Expand Up @@ -39,6 +39,16 @@ use crate::mem::MaybeUninit;
/// Ok(())
/// }
/// ```
///
/// # Platform-specific behavior
///
/// On Linux (including Android), this function uses `copy_file_range(2)`,
/// `sendfile(2)` or `splice(2)` syscalls to move data directly between file
/// descriptors if possible.
///
/// Note that platform-specific behavior [may change in the future][changes].
///
/// [changes]: crate::io#platform-specific-behavior
#[stable(feature = "rust1", since = "1.0.0")]
pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> Result<u64>
where
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