diff options
| -rw-r--r-- | library/std/src/os/unix/fs.rs | 28 |
1 files changed, 25 insertions, 3 deletions
diff --git a/library/std/src/os/unix/fs.rs b/library/std/src/os/unix/fs.rs index 358ab33fffd..19d9e89a631 100644 --- a/library/std/src/os/unix/fs.rs +++ b/library/std/src/os/unix/fs.rs @@ -150,9 +150,31 @@ pub trait FileExt { /// short write. /// /// # Bug - /// On some systems, due to a [bug] with [`pwrite64`] (the underlying - /// syscall), files opened with the `O_APPEND` flag fail to respect the - /// offset parameter, always appending to the end of the file instead. + /// On some systems, `write_at` utilises [`pwrite64`] to write to files. + /// However, this syscall has a [bug] where files opened with the `O_APPEND` + /// flag fail to respect the offset parameter, always appending to the end + /// of the file instead. + /// + /// It is possible to inadvertantly set this flag, like in the example below. + /// Therefore, it is important to be vigilant while changing options to mitigate + /// unexpected behaviour. + /// + /// ```no_run + /// use std::fs::File; + /// use std::io; + /// use std::os::unix::prelude::FileExt; + /// + /// fn main() -> io::Result<()> { + /// // Open a file with the append option (sets the `O_APPEND` flag) + /// let file = File::options().append(true).open("foo.txt")?; + /// + /// // We attempt to write at offset 10; instead appended to EOF + /// file.write_at(b"sushi", 10)?; + /// + /// // foo.txt is 5 bytes long instead of 15 + /// Ok(()) + /// } + /// ``` /// /// [`File::write`]: fs::File::write /// [`pwrite64`]: https://man7.org/linux/man-pages/man2/pwrite.2.html |