diff options
Diffstat (limited to 'library/std/src/sys/pal/unix/kernel_copy.rs')
| -rw-r--r-- | library/std/src/sys/pal/unix/kernel_copy.rs | 730 |
1 files changed, 730 insertions, 0 deletions
diff --git a/library/std/src/sys/pal/unix/kernel_copy.rs b/library/std/src/sys/pal/unix/kernel_copy.rs new file mode 100644 index 00000000000..18acd5ecccd --- /dev/null +++ b/library/std/src/sys/pal/unix/kernel_copy.rs @@ -0,0 +1,730 @@ +//! This module contains specializations that can offload `io::copy()` operations on file descriptor +//! containing types (`File`, `TcpStream`, etc.) to more efficient syscalls than `read(2)` and `write(2)`. +//! +//! Specialization is only applied to wholly std-owned types so that user code can't observe +//! that the `Read` and `Write` traits are not used. +//! +//! Since a copy operation involves a reader and writer side where each can consist of different types +//! and also involve generic wrappers (e.g. `Take`, `BufReader`) it is not practical to specialize +//! a single method on all possible combinations. +//! +//! Instead readers and writers are handled separately by the `CopyRead` and `CopyWrite` specialization +//! traits and then specialized on by the `Copier::copy` method. +//! +//! `Copier` uses the specialization traits to unpack the underlying file descriptors and +//! additional prerequisites and constraints imposed by the wrapper types. +//! +//! Once it has obtained all necessary pieces and brought any wrapper types into a state where they +//! can be safely bypassed it will attempt to use the `copy_file_range(2)`, +//! `sendfile(2)` or `splice(2)` syscalls to move data directly between file descriptors. +//! Since those syscalls have requirements that cannot be fully checked in advance it attempts +//! to use them one after another (guided by hints) to figure out which one works and +//! falls back to the generic read-write copy loop if none of them does. +//! Once a working syscall is found for a pair of file descriptors it will be called in a loop +//! until the copy operation is completed. +//! +//! Advantages of using these syscalls: +//! +//! * fewer context switches since reads and writes are coalesced into a single syscall +//! and more bytes are transferred per syscall. This translates to higher throughput +//! and fewer CPU cycles, at least for sufficiently large transfers to amortize the initial probing. +//! * `copy_file_range` creates reflink copies on CoW filesystems, thus moving less data and +//! consuming less disk space +//! * `sendfile` and `splice` can perform zero-copy IO under some circumstances while +//! a naive copy loop would move every byte through the CPU. +//! +//! Drawbacks: +//! +//! * copy operations smaller than the default buffer size can under some circumstances, especially +//! on older kernels, incur more syscalls than the naive approach would. As mentioned above +//! the syscall selection is guided by hints to minimize this possibility but they are not perfect. +//! * optimizations only apply to std types. If a user adds a custom wrapper type, e.g. to report +//! progress, they can hit a performance cliff. +//! * complexity + +use crate::cmp::min; +use crate::fs::{File, Metadata}; +use crate::io::copy::generic_copy; +use crate::io::{ + BufRead, BufReader, BufWriter, Error, Read, Result, StderrLock, StdinLock, StdoutLock, Take, + Write, +}; +use crate::mem::ManuallyDrop; +use crate::net::TcpStream; +use crate::os::unix::fs::FileTypeExt; +use crate::os::unix::io::{AsRawFd, FromRawFd, RawFd}; +use crate::os::unix::net::UnixStream; +use crate::process::{ChildStderr, ChildStdin, ChildStdout}; +use crate::ptr; +use crate::sync::atomic::{AtomicBool, AtomicU8, Ordering}; +use crate::sys::cvt; +use crate::sys::weak::syscall; +#[cfg(not(any(all(target_os = "linux", target_env = "gnu"), target_os = "hurd")))] +use libc::sendfile as sendfile64; +#[cfg(any(all(target_os = "linux", target_env = "gnu"), target_os = "hurd"))] +use libc::sendfile64; +use libc::{EBADF, EINVAL, ENOSYS, EOPNOTSUPP, EOVERFLOW, EPERM, EXDEV}; + +#[cfg(test)] +mod tests; + +pub(crate) fn copy_spec<R: Read + ?Sized, W: Write + ?Sized>( + read: &mut R, + write: &mut W, +) -> Result<u64> { + let copier = Copier { read, write }; + SpecCopy::copy(copier) +} + +/// This type represents either the inferred `FileType` of a `RawFd` based on the source +/// type from which it was extracted or the actual metadata +/// +/// The methods on this type only provide hints, due to `AsRawFd` and `FromRawFd` the inferred +/// type may be wrong. +enum FdMeta { + Metadata(Metadata), + Socket, + Pipe, + /// We don't have any metadata because the stat syscall failed + NoneObtained, +} + +#[derive(PartialEq)] +enum FdHandle { + Input, + Output, +} + +impl FdMeta { + fn maybe_fifo(&self) -> bool { + match self { + FdMeta::Metadata(meta) => meta.file_type().is_fifo(), + FdMeta::Socket => false, + FdMeta::Pipe => true, + FdMeta::NoneObtained => true, + } + } + + fn potential_sendfile_source(&self) -> bool { + match self { + // procfs erroneously shows 0 length on non-empty readable files. + // and if a file is truly empty then a `read` syscall will determine that and skip the write syscall + // thus there would be benefit from attempting sendfile + FdMeta::Metadata(meta) + if meta.file_type().is_file() && meta.len() > 0 + || meta.file_type().is_block_device() => + { + true + } + _ => false, + } + } + + fn copy_file_range_candidate(&self, f: FdHandle) -> bool { + match self { + // copy_file_range will fail on empty procfs files. `read` can determine whether EOF has been reached + // without extra cost and skip the write, thus there is no benefit in attempting copy_file_range + FdMeta::Metadata(meta) if f == FdHandle::Input && meta.is_file() && meta.len() > 0 => { + true + } + FdMeta::Metadata(meta) if f == FdHandle::Output && meta.is_file() => true, + _ => false, + } + } +} + +/// Returns true either if changes made to the source after a sendfile/splice call won't become +/// visible in the sink or the source has explicitly opted into such behavior (e.g. by splicing +/// a file into a pipe, the pipe being the source in this case). +/// +/// This will prevent File -> Pipe and File -> Socket splicing/sendfile optimizations to uphold +/// the Read/Write API semantics of io::copy. +/// +/// Note: This is not 100% airtight, the caller can use the RawFd conversion methods to turn a +/// regular file into a TcpSocket which will be treated as a socket here without checking. +fn safe_kernel_copy(source: &FdMeta, sink: &FdMeta) -> bool { + match (source, sink) { + // Data arriving from a socket is safe because the sender can't modify the socket buffer. + // Data arriving from a pipe is safe(-ish) because either the sender *copied* + // the bytes into the pipe OR explicitly performed an operation that enables zero-copy, + // thus promising not to modify the data later. + (FdMeta::Socket, _) => true, + (FdMeta::Pipe, _) => true, + (FdMeta::Metadata(meta), _) + if meta.file_type().is_fifo() || meta.file_type().is_socket() => + { + true + } + // Data going into non-pipes/non-sockets is safe because the "later changes may become visible" issue + // only happens for pages sitting in send buffers or pipes. + (_, FdMeta::Metadata(meta)) + if !meta.file_type().is_fifo() && !meta.file_type().is_socket() => + { + true + } + _ => false, + } +} + +struct CopyParams(FdMeta, Option<RawFd>); + +struct Copier<'a, 'b, R: Read + ?Sized, W: Write + ?Sized> { + read: &'a mut R, + write: &'b mut W, +} + +trait SpecCopy { + fn copy(self) -> Result<u64>; +} + +impl<R: Read + ?Sized, W: Write + ?Sized> SpecCopy for Copier<'_, '_, R, W> { + default fn copy(self) -> Result<u64> { + generic_copy(self.read, self.write) + } +} + +impl<R: CopyRead, W: CopyWrite> SpecCopy for Copier<'_, '_, R, W> { + fn copy(self) -> Result<u64> { + let (reader, writer) = (self.read, self.write); + let r_cfg = reader.properties(); + let w_cfg = writer.properties(); + + // before direct operations on file descriptors ensure that all source and sink buffers are empty + let mut flush = || -> crate::io::Result<u64> { + let bytes = reader.drain_to(writer, u64::MAX)?; + // BufWriter buffered bytes have already been accounted for in earlier write() calls + writer.flush()?; + Ok(bytes) + }; + + let mut written = 0u64; + + if let (CopyParams(input_meta, Some(readfd)), CopyParams(output_meta, Some(writefd))) = + (r_cfg, w_cfg) + { + written += flush()?; + let max_write = reader.min_limit(); + + if input_meta.copy_file_range_candidate(FdHandle::Input) + && output_meta.copy_file_range_candidate(FdHandle::Output) + { + let result = copy_regular_files(readfd, writefd, max_write); + result.update_take(reader); + + match result { + CopyResult::Ended(bytes_copied) => return Ok(bytes_copied + written), + CopyResult::Error(e, _) => return Err(e), + CopyResult::Fallback(bytes) => written += bytes, + } + } + + // on modern kernels sendfile can copy from any mmapable type (some but not all regular files and block devices) + // to any writable file descriptor. On older kernels the writer side can only be a socket. + // So we just try and fallback if needed. + // If current file offsets + write sizes overflow it may also fail, we do not try to fix that and instead + // fall back to the generic copy loop. + if input_meta.potential_sendfile_source() && safe_kernel_copy(&input_meta, &output_meta) + { + let result = sendfile_splice(SpliceMode::Sendfile, readfd, writefd, max_write); + result.update_take(reader); + + match result { + CopyResult::Ended(bytes_copied) => return Ok(bytes_copied + written), + CopyResult::Error(e, _) => return Err(e), + CopyResult::Fallback(bytes) => written += bytes, + } + } + + if (input_meta.maybe_fifo() || output_meta.maybe_fifo()) + && safe_kernel_copy(&input_meta, &output_meta) + { + let result = sendfile_splice(SpliceMode::Splice, readfd, writefd, max_write); + result.update_take(reader); + + match result { + CopyResult::Ended(bytes_copied) => return Ok(bytes_copied + written), + CopyResult::Error(e, _) => return Err(e), + CopyResult::Fallback(0) => { /* use the fallback below */ } + CopyResult::Fallback(_) => { + unreachable!("splice should not return > 0 bytes on the fallback path") + } + } + } + } + + // fallback if none of the more specialized syscalls wants to work with these file descriptors + match generic_copy(reader, writer) { + Ok(bytes) => Ok(bytes + written), + err => err, + } + } +} + +#[rustc_specialization_trait] +trait CopyRead: Read { + /// Implementations that contain buffers (i.e. `BufReader`) must transfer data from their internal + /// buffers into `writer` until either the buffers are emptied or `limit` bytes have been + /// transferred, whichever occurs sooner. + /// If nested buffers are present the outer buffers must be drained first. + /// + /// This is necessary to directly bypass the wrapper types while preserving the data order + /// when operating directly on the underlying file descriptors. + fn drain_to<W: Write>(&mut self, _writer: &mut W, _limit: u64) -> Result<u64> { + Ok(0) + } + + /// Updates `Take` wrappers to remove the number of bytes copied. + fn taken(&mut self, _bytes: u64) {} + + /// The minimum of the limit of all `Take<_>` wrappers, `u64::MAX` otherwise. + /// This method does not account for data `BufReader` buffers and would underreport + /// the limit of a `Take<BufReader<Take<_>>>` type. Thus its result is only valid + /// after draining the buffers via `drain_to`. + fn min_limit(&self) -> u64 { + u64::MAX + } + + /// Extracts the file descriptor and hints/metadata, delegating through wrappers if necessary. + fn properties(&self) -> CopyParams; +} + +#[rustc_specialization_trait] +trait CopyWrite: Write { + /// Extracts the file descriptor and hints/metadata, delegating through wrappers if necessary. + fn properties(&self) -> CopyParams; +} + +impl<T> CopyRead for &mut T +where + T: CopyRead, +{ + fn drain_to<W: Write>(&mut self, writer: &mut W, limit: u64) -> Result<u64> { + (**self).drain_to(writer, limit) + } + + fn taken(&mut self, bytes: u64) { + (**self).taken(bytes); + } + + fn min_limit(&self) -> u64 { + (**self).min_limit() + } + + fn properties(&self) -> CopyParams { + (**self).properties() + } +} + +impl<T> CopyWrite for &mut T +where + T: CopyWrite, +{ + fn properties(&self) -> CopyParams { + (**self).properties() + } +} + +impl CopyRead for File { + fn properties(&self) -> CopyParams { + CopyParams(fd_to_meta(self), Some(self.as_raw_fd())) + } +} + +impl CopyRead for &File { + fn properties(&self) -> CopyParams { + CopyParams(fd_to_meta(*self), Some(self.as_raw_fd())) + } +} + +impl CopyWrite for File { + fn properties(&self) -> CopyParams { + CopyParams(fd_to_meta(self), Some(self.as_raw_fd())) + } +} + +impl CopyWrite for &File { + fn properties(&self) -> CopyParams { + CopyParams(fd_to_meta(*self), Some(self.as_raw_fd())) + } +} + +impl CopyRead for TcpStream { + fn properties(&self) -> CopyParams { + // avoid the stat syscall since we can be fairly sure it's a socket + CopyParams(FdMeta::Socket, Some(self.as_raw_fd())) + } +} + +impl CopyRead for &TcpStream { + fn properties(&self) -> CopyParams { + // avoid the stat syscall since we can be fairly sure it's a socket + CopyParams(FdMeta::Socket, Some(self.as_raw_fd())) + } +} + +impl CopyWrite for TcpStream { + fn properties(&self) -> CopyParams { + // avoid the stat syscall since we can be fairly sure it's a socket + CopyParams(FdMeta::Socket, Some(self.as_raw_fd())) + } +} + +impl CopyWrite for &TcpStream { + fn properties(&self) -> CopyParams { + // avoid the stat syscall since we can be fairly sure it's a socket + CopyParams(FdMeta::Socket, Some(self.as_raw_fd())) + } +} + +impl CopyRead for UnixStream { + fn properties(&self) -> CopyParams { + // avoid the stat syscall since we can be fairly sure it's a socket + CopyParams(FdMeta::Socket, Some(self.as_raw_fd())) + } +} + +impl CopyRead for &UnixStream { + fn properties(&self) -> CopyParams { + // avoid the stat syscall since we can be fairly sure it's a socket + CopyParams(FdMeta::Socket, Some(self.as_raw_fd())) + } +} + +impl CopyWrite for UnixStream { + fn properties(&self) -> CopyParams { + // avoid the stat syscall since we can be fairly sure it's a socket + CopyParams(FdMeta::Socket, Some(self.as_raw_fd())) + } +} + +impl CopyWrite for &UnixStream { + fn properties(&self) -> CopyParams { + // avoid the stat syscall since we can be fairly sure it's a socket + CopyParams(FdMeta::Socket, Some(self.as_raw_fd())) + } +} + +impl CopyWrite for ChildStdin { + fn properties(&self) -> CopyParams { + CopyParams(FdMeta::Pipe, Some(self.as_raw_fd())) + } +} + +impl CopyRead for ChildStdout { + fn properties(&self) -> CopyParams { + CopyParams(FdMeta::Pipe, Some(self.as_raw_fd())) + } +} + +impl CopyRead for ChildStderr { + fn properties(&self) -> CopyParams { + CopyParams(FdMeta::Pipe, Some(self.as_raw_fd())) + } +} + +impl CopyRead for StdinLock<'_> { + fn drain_to<W: Write>(&mut self, writer: &mut W, outer_limit: u64) -> Result<u64> { + let buf_reader = self.as_mut_buf(); + let buf = buf_reader.buffer(); + let buf = &buf[0..min(buf.len(), outer_limit.try_into().unwrap_or(usize::MAX))]; + let bytes_drained = buf.len(); + writer.write_all(buf)?; + buf_reader.consume(bytes_drained); + + Ok(bytes_drained as u64) + } + + fn properties(&self) -> CopyParams { + CopyParams(fd_to_meta(self), Some(self.as_raw_fd())) + } +} + +impl CopyWrite for StdoutLock<'_> { + fn properties(&self) -> CopyParams { + CopyParams(fd_to_meta(self), Some(self.as_raw_fd())) + } +} + +impl CopyWrite for StderrLock<'_> { + fn properties(&self) -> CopyParams { + CopyParams(fd_to_meta(self), Some(self.as_raw_fd())) + } +} + +impl<T: CopyRead> CopyRead for Take<T> { + fn drain_to<W: Write>(&mut self, writer: &mut W, outer_limit: u64) -> Result<u64> { + let local_limit = self.limit(); + let combined_limit = min(outer_limit, local_limit); + let bytes_drained = self.get_mut().drain_to(writer, combined_limit)?; + // update limit since read() was bypassed + self.set_limit(local_limit - bytes_drained); + + Ok(bytes_drained) + } + + fn taken(&mut self, bytes: u64) { + self.set_limit(self.limit() - bytes); + self.get_mut().taken(bytes); + } + + fn min_limit(&self) -> u64 { + min(Take::limit(self), self.get_ref().min_limit()) + } + + fn properties(&self) -> CopyParams { + self.get_ref().properties() + } +} + +impl<T: ?Sized + CopyRead> CopyRead for BufReader<T> { + fn drain_to<W: Write>(&mut self, writer: &mut W, outer_limit: u64) -> Result<u64> { + let buf = self.buffer(); + let buf = &buf[0..min(buf.len(), outer_limit.try_into().unwrap_or(usize::MAX))]; + let bytes = buf.len(); + writer.write_all(buf)?; + self.consume(bytes); + + let remaining = outer_limit - bytes as u64; + + // in case of nested bufreaders we also need to drain the ones closer to the source + let inner_bytes = self.get_mut().drain_to(writer, remaining)?; + + Ok(bytes as u64 + inner_bytes) + } + + fn taken(&mut self, bytes: u64) { + self.get_mut().taken(bytes); + } + + fn min_limit(&self) -> u64 { + self.get_ref().min_limit() + } + + fn properties(&self) -> CopyParams { + self.get_ref().properties() + } +} + +impl<T: ?Sized + CopyWrite> CopyWrite for BufWriter<T> { + fn properties(&self) -> CopyParams { + self.get_ref().properties() + } +} + +fn fd_to_meta<T: AsRawFd>(fd: &T) -> FdMeta { + let fd = fd.as_raw_fd(); + let file: ManuallyDrop<File> = ManuallyDrop::new(unsafe { File::from_raw_fd(fd) }); + match file.metadata() { + Ok(meta) => FdMeta::Metadata(meta), + Err(_) => FdMeta::NoneObtained, + } +} + +pub(super) enum CopyResult { + Ended(u64), + Error(Error, u64), + Fallback(u64), +} + +impl CopyResult { + fn update_take(&self, reader: &mut impl CopyRead) { + match *self { + CopyResult::Fallback(bytes) + | CopyResult::Ended(bytes) + | CopyResult::Error(_, bytes) => reader.taken(bytes), + } + } +} + +/// Invalid file descriptor. +/// +/// Valid file descriptors are guaranteed to be positive numbers (see `open()` manpage) +/// while negative values are used to indicate errors. +/// Thus -1 will never be overlap with a valid open file. +const INVALID_FD: RawFd = -1; + +/// Linux-specific implementation that will attempt to use copy_file_range for copy offloading. +/// As the name says, it only works on regular files. +/// +/// Callers must handle fallback to a generic copy loop. +/// `Fallback` may indicate non-zero number of bytes already written +/// if one of the files' cursor +`max_len` would exceed u64::MAX (`EOVERFLOW`). +pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) -> CopyResult { + use crate::cmp; + + const NOT_PROBED: u8 = 0; + const UNAVAILABLE: u8 = 1; + const AVAILABLE: u8 = 2; + + // Kernel prior to 4.5 don't have copy_file_range + // We store the availability in a global to avoid unnecessary syscalls + static HAS_COPY_FILE_RANGE: AtomicU8 = AtomicU8::new(NOT_PROBED); + + syscall! { + fn copy_file_range( + fd_in: libc::c_int, + off_in: *mut libc::loff_t, + fd_out: libc::c_int, + off_out: *mut libc::loff_t, + len: libc::size_t, + flags: libc::c_uint + ) -> libc::ssize_t + } + + match HAS_COPY_FILE_RANGE.load(Ordering::Relaxed) { + NOT_PROBED => { + // EPERM can indicate seccomp filters or an immutable file. + // To distinguish these cases we probe with invalid file descriptors which should result in EBADF if the syscall is supported + // and some other error (ENOSYS or EPERM) if it's not available + let result = unsafe { + cvt(copy_file_range(INVALID_FD, ptr::null_mut(), INVALID_FD, ptr::null_mut(), 1, 0)) + }; + + if matches!(result.map_err(|e| e.raw_os_error()), Err(Some(EBADF))) { + HAS_COPY_FILE_RANGE.store(AVAILABLE, Ordering::Relaxed); + } else { + HAS_COPY_FILE_RANGE.store(UNAVAILABLE, Ordering::Relaxed); + return CopyResult::Fallback(0); + } + } + UNAVAILABLE => return CopyResult::Fallback(0), + _ => {} + }; + + let mut written = 0u64; + while written < max_len { + let bytes_to_copy = cmp::min(max_len - written, usize::MAX as u64); + // cap to 1GB chunks in case u64::MAX is passed as max_len and the file has a non-zero seek position + // this allows us to copy large chunks without hitting EOVERFLOW, + // unless someone sets a file offset close to u64::MAX - 1GB, in which case a fallback would be required + let bytes_to_copy = cmp::min(bytes_to_copy as usize, 0x4000_0000usize); + let copy_result = unsafe { + // We actually don't have to adjust the offsets, + // because copy_file_range adjusts the file offset automatically + cvt(copy_file_range(reader, ptr::null_mut(), writer, ptr::null_mut(), bytes_to_copy, 0)) + }; + + match copy_result { + Ok(0) if written == 0 => { + // fallback to work around several kernel bugs where copy_file_range will fail to + // copy any bytes and return 0 instead of an error if + // - reading virtual files from the proc filesystem which appear to have 0 size + // but are not empty. noted in coreutils to affect kernels at least up to 5.6.19. + // - copying from an overlay filesystem in docker. reported to occur on fedora 32. + return CopyResult::Fallback(0); + } + Ok(0) => return CopyResult::Ended(written), // reached EOF + Ok(ret) => written += ret as u64, + Err(err) => { + return match err.raw_os_error() { + // when file offset + max_length > u64::MAX + Some(EOVERFLOW) => CopyResult::Fallback(written), + Some(ENOSYS | EXDEV | EINVAL | EPERM | EOPNOTSUPP | EBADF) if written == 0 => { + // Try fallback io::copy if either: + // - Kernel version is < 4.5 (ENOSYS¹) + // - Files are mounted on different fs (EXDEV) + // - copy_file_range is broken in various ways on RHEL/CentOS 7 (EOPNOTSUPP) + // - copy_file_range file is immutable or syscall is blocked by seccomp¹ (EPERM) + // - copy_file_range cannot be used with pipes or device nodes (EINVAL) + // - the writer fd was opened with O_APPEND (EBADF²) + // and no bytes were written successfully yet. (All these errnos should + // not be returned if something was already written, but they happen in + // the wild, see #91152.) + // + // ¹ these cases should be detected by the initial probe but we handle them here + // anyway in case syscall interception changes during runtime + // ² actually invalid file descriptors would cause this too, but in that case + // the fallback code path is expected to encounter the same error again + CopyResult::Fallback(0) + } + _ => CopyResult::Error(err, written), + }; + } + } + } + CopyResult::Ended(written) +} + +#[derive(PartialEq)] +enum SpliceMode { + Sendfile, + Splice, +} + +/// performs splice or sendfile between file descriptors +/// Does _not_ fall back to a generic copy loop. +fn sendfile_splice(mode: SpliceMode, reader: RawFd, writer: RawFd, len: u64) -> CopyResult { + static HAS_SENDFILE: AtomicBool = AtomicBool::new(true); + static HAS_SPLICE: AtomicBool = AtomicBool::new(true); + + // Android builds use feature level 14, but the libc wrapper for splice is + // gated on feature level 21+, so we have to invoke the syscall directly. + #[cfg(target_os = "android")] + syscall! { + fn splice( + srcfd: libc::c_int, + src_offset: *const i64, + dstfd: libc::c_int, + dst_offset: *const i64, + len: libc::size_t, + flags: libc::c_int + ) -> libc::ssize_t + } + + #[cfg(target_os = "linux")] + use libc::splice; + + match mode { + SpliceMode::Sendfile if !HAS_SENDFILE.load(Ordering::Relaxed) => { + return CopyResult::Fallback(0); + } + SpliceMode::Splice if !HAS_SPLICE.load(Ordering::Relaxed) => { + return CopyResult::Fallback(0); + } + _ => (), + } + + let mut written = 0u64; + while written < len { + // according to its manpage that's the maximum size sendfile() will copy per invocation + let chunk_size = crate::cmp::min(len - written, 0x7ffff000_u64) as usize; + + let result = match mode { + SpliceMode::Sendfile => { + cvt(unsafe { sendfile64(writer, reader, ptr::null_mut(), chunk_size) }) + } + SpliceMode::Splice => cvt(unsafe { + splice(reader, ptr::null_mut(), writer, ptr::null_mut(), chunk_size, 0) + }), + }; + + match result { + Ok(0) => break, // EOF + Ok(ret) => written += ret as u64, + Err(err) => { + return match err.raw_os_error() { + Some(ENOSYS | EPERM) => { + // syscall not supported (ENOSYS) + // syscall is disallowed, e.g. by seccomp (EPERM) + match mode { + SpliceMode::Sendfile => HAS_SENDFILE.store(false, Ordering::Relaxed), + SpliceMode::Splice => HAS_SPLICE.store(false, Ordering::Relaxed), + } + assert_eq!(written, 0); + CopyResult::Fallback(0) + } + Some(EINVAL) => { + // splice/sendfile do not support this particular file descriptor (EINVAL) + assert_eq!(written, 0); + CopyResult::Fallback(0) + } + Some(os_err) if mode == SpliceMode::Sendfile && os_err == EOVERFLOW => { + CopyResult::Fallback(written) + } + _ => CopyResult::Error(err, written), + }; + } + } + } + CopyResult::Ended(written) +} |