diff options
| -rw-r--r-- | library/std/src/io/mod.rs | 19 |
1 files changed, 10 insertions, 9 deletions
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs index dd178b357df..21942ef5031 100644 --- a/library/std/src/io/mod.rs +++ b/library/std/src/io/mod.rs @@ -263,15 +263,16 @@ //! allocator or a memory mapping library) and now accessing the file descriptor will interfere in //! arbitrarily destructive ways with that other library. //! -//! Note that this does not talk about performing other operations on the file descriptor, such as -//! reading or writing. For example, on Unix, the [`OwnedFd`] and [`BorrowedFd`] types from the -//! standard library do *not* exclude that there is other code that reads or writes the same -//! underlying object, and indeed there exist safe functions like `BorrowedFd::try_clone_to_owned` -//! that can be used to read or write an object even after the end of the borrow. However, user code -//! might want to rely on keeping the object behind a file descriptor completely private and -//! protected against reads or writes from other parts of the program. Whether that is sound is -//! [currently unclear](https://github.com/rust-lang/rust/issues/114167). Certainly, `OwnedFd` as a -//! type does not provide any promise that the underlying file descriptor has not been cloned. +//! Note that exclusive ownership of a file descriptor does *not* imply exclusive ownership of the +//! underlying kernel object that the file descriptor references (also called "file description" on +//! some operating systems). An owned file descriptor can have duplicates, i.e., other file +//! descriptors that share the same kernel object. The exact rules around ownership of kernel +//! objects are [still unclear](https://github.com/rust-lang/rust/issues/114167). Until that is +//! clarified, the general advice is not to perform *any* operations on file descriptors that were +//! never borrowed to or owned by you. In other words, receiving a borrowed file descriptor *does* +//! give you the right to make a duplicate and use that duplicate beyond the end of the borrow, but +//! nothing gives you the right to just `write` to a file descriptor that never even got borrowed to +//! you. //! //! [`File`]: crate::fs::File //! [`TcpStream`]: crate::net::TcpStream |