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// Unless explicitly stated otherwise all files in this repository are licensed // under the MIT/Apache-2.0 License, at your convenience // // This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2020 Datadog, Inc. //! `glommio::io` provides data structures targeted towards File I/O. //! //! File I/O in Glommio comes in two kinds: Buffered and Direct I/O. //! //! Ideally an application would pick one of them according to its needs and not //! mix both. However if you do want to mix both, it is recommended that you do //! not do so in the same device: Kernel settings like I/O schedulers and merge //! settings that are beneficial to one of them can be detrimental to the //! others. //! //! If you absolutely must use both in the same device, avoid issuing both //! Direct and Buffered I/O in the same file: at this point you are just trying //! to drive Linux crazy. //! //! Buffered I/O //! ============ //! //! Buffered I/O will use the operating system page cache. It is ideal for //! simpler applications that don't want to deal with caching policies and have //! I/O performance as a maybe important, but definitely not crucial part of //! their performance story. //! //! Disadvantages of Buffered I/O: //! * Hard to know when resources are really used, which make controlled //! processes almost impossible (the time of write to device is detached from //! the file write time) //! * More copies than necessary, as the data has to be copied from the device //! to the page cache, from the page cache to the internal file buffers, and //! in abstract linear implementations like [`AsyncWriteExt`] and //! [`AsyncReadExt`] from user-provided buffers to the file internal buffers. //! * Advanced features for io_uring like Non-interrupt mode, registered files, //! registered buffers, will not work with Buffered I/O //! * Read amplification for small random reads, as the OS is bounded by the //! page size (usually 4kB), even though modern NVMe devices are perfectly //! capable of issuing 512-byte I/O. //! //! The main structure to deal with Buffered I/O is the [`BufferedFile`] struct. //! It is targeted at random I/O. Reads from and writes to it expect a position. //! //! Direct I/O //! ========== //! //! Direct I/O will not use the Operating System page cache and will always //! touch the device directly. That will always work very well for stream-based //! workloads (scanning a file much larger than memory, writing a buffer that //! will not be read from in the near future, etc) but will require a //! user-provided cache for good random performance. //! //! There are advantages to using a user-provided cache: Files usually contain //! serialized objects and every read have to deserialize them. A user-provided //! cache can cache the parsed objects, among others. Still, not all //! applications can or want to deal with that complexity. //! //! Disadvantages of Direct I/O: //! * I/O needs to be aligned. Both the buffers and the file positions need //! specific alignments. The [`DmaBuffer`] should hide most of that //! complexity, but you may still end up with heavy read amplification if you //! are not careful. //! * Without a user-provided cache, random performance can be bad. //! //! There are two main structs that deal with File Direct I/O: //! //! [`DmaFile`] is targeted at random Direct I/O. Reads from and writes to it //! expect a position. //! //! [`DmaStreamWriter`] and [`DmaStreamReader`] perform sequential I/O and their //! interface is a lot closer to other mainstream rust interfaces in `std::fs`. //! //! However, despite being sequential, I/O for the two Stream structs are //! parallel: [`DmaStreamWriter`] exposes a setting for write-behind, meaning //! that it will keep accepting writes to its internal buffers even with older //! writes are still in-flight. In turn, [`DmaStreamReader`] exposes a setting //! for read-ahead meaning it will initiate I/O for positions you will read into //! the future sooner. //! //! [`BufferedFile`]: struct.BufferedFile.html //! [`DmaFile`]: struct.DmaFile.html //! [`DmaBuffer`]: struct.DmaBuffer.html //! [`DmaStreamWriter`]: struct.DmaStreamWriter.html //! [`DmaStreamReader`]: struct.DmaStreamReader.html //! [`AsyncReadExt`]: https://docs.rs/futures-lite/1.11.2/futures_lite/io/trait.AsyncReadExt.html //! [`AsyncWriteExt`]: https://docs.rs/futures-lite/1.11.2/futures_lite/io/trait.AsyncWriteExt.html macro_rules! enhanced_try { ($expr:expr, $op:expr, $path:expr, $fd:expr) => {{ match $expr { Ok(val) => Ok(val), Err(source) => { let enhanced = crate::error::GlommioError::<()>::EnhancedIoError { source, op: $op, path: $path.and_then(|x| Some(x.to_path_buf())), fd: $fd, }; Err(enhanced) } } }}; ($expr:expr, $op:expr, $obj:expr) => {{ enhanced_try!( $expr, $op, $obj.path.as_ref().and_then(|x| Some(x.as_path())), Some($obj.as_raw_fd()) ) }}; } mod buffered_file; mod buffered_file_stream; mod directory; mod dma_file; mod dma_file_stream; mod dma_open_options; mod glommio_file; mod read_result; use crate::sys; use std::path::Path; pub(super) type Result<T> = crate::Result<T, ()>; /// rename an existing file. /// /// Warning: synchronous operation, will block the reactor pub async fn rename<P: AsRef<Path>, Q: AsRef<Path>>(old_path: P, new_path: Q) -> Result<()> { sys::rename_file(&old_path.as_ref(), &new_path.as_ref())?; Ok(()) } /// remove an existing file given its name /// /// Warning: synchronous operation, will block the reactor pub async fn remove<P: AsRef<Path>>(path: P) -> Result<()> { enhanced_try!( sys::remove_file(path.as_ref()), "Removing", Some(path.as_ref()), None ) } pub use self::{ buffered_file::BufferedFile, buffered_file_stream::{ stdin, StreamReader, StreamReaderBuilder, StreamWriter, StreamWriterBuilder, }, directory::Directory, dma_file::DmaFile, dma_file_stream::{ DmaStreamReader, DmaStreamReaderBuilder, DmaStreamWriter, DmaStreamWriterBuilder, }, dma_open_options::DmaOpenOptions, read_result::ReadResult, }; pub use crate::sys::DmaBuffer; #[cfg(test)] mod test { use super::*; use crate::LocalExecutor; #[test] fn remove_nonexistent() { let local_ex = LocalExecutor::default(); local_ex.run(async { let x = remove("/tmp/this_file_does_not_exist_and_if_you_created_just_to_mess_with_me_you_deserve_this_test_to_fail_and_I_am_not_even_sorry").await; assert_eq!(x.unwrap_err().raw_os_error().unwrap(), libc::ENOENT); }); } }