| // Copyright 2020 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package os |
| |
| import ( |
| "internal/poll" |
| "io" |
| "syscall" |
| ) |
| |
| var ( |
| pollCopyFileRange = poll.CopyFileRange |
| pollSplice = poll.Splice |
| ) |
| |
| func (f *File) readFrom(r io.Reader) (written int64, handled bool, err error) { |
| // Neither copy_file_range(2) nor splice(2) supports destinations opened with |
| // O_APPEND, so don't bother to try zero-copy with these system calls. |
| // |
| // Visit https://man7.org/linux/man-pages/man2/copy_file_range.2.html#ERRORS and |
| // https://man7.org/linux/man-pages/man2/splice.2.html#ERRORS for details. |
| if f.appendMode { |
| return 0, false, nil |
| } |
| |
| written, handled, err = f.copyFileRange(r) |
| if handled { |
| return |
| } |
| return f.spliceToFile(r) |
| } |
| |
| func (f *File) spliceToFile(r io.Reader) (written int64, handled bool, err error) { |
| var ( |
| remain int64 |
| lr *io.LimitedReader |
| ) |
| if lr, r, remain = tryLimitedReader(r); remain <= 0 { |
| return 0, true, nil |
| } |
| |
| pfd := getPollFD(r) |
| // TODO(panjf2000): run some tests to see if we should unlock the non-streams for splice. |
| // Streams benefit the most from the splice(2), non-streams are not even supported in old kernels |
| // where splice(2) will just return EINVAL; newer kernels support non-streams like UDP, but I really |
| // doubt that splice(2) could help non-streams, cuz they usually send small frames respectively |
| // and one splice call would result in one frame. |
| // splice(2) is suitable for large data but the generation of fragments defeats its edge here. |
| // Therefore, don't bother to try splice if the r is not a streaming descriptor. |
| if pfd == nil || !pfd.IsStream { |
| return |
| } |
| |
| var syscallName string |
| written, handled, syscallName, err = pollSplice(&f.pfd, pfd, remain) |
| |
| if lr != nil { |
| lr.N = remain - written |
| } |
| |
| return written, handled, wrapSyscallError(syscallName, err) |
| } |
| |
| // getPollFD tries to get the poll.FD from the given io.Reader by expecting |
| // the underlying type of r to be the implementation of syscall.Conn that contains |
| // a *net.rawConn. |
| func getPollFD(r io.Reader) *poll.FD { |
| sc, ok := r.(syscall.Conn) |
| if !ok { |
| return nil |
| } |
| rc, err := sc.SyscallConn() |
| if err != nil { |
| return nil |
| } |
| ipfd, ok := rc.(interface{ PollFD() *poll.FD }) |
| if !ok { |
| return nil |
| } |
| return ipfd.PollFD() |
| } |
| |
| func (f *File) copyFileRange(r io.Reader) (written int64, handled bool, err error) { |
| var ( |
| remain int64 |
| lr *io.LimitedReader |
| ) |
| if lr, r, remain = tryLimitedReader(r); remain <= 0 { |
| return 0, true, nil |
| } |
| |
| src, ok := r.(*File) |
| if !ok { |
| return 0, false, nil |
| } |
| if src.checkValid("ReadFrom") != nil { |
| // Avoid returning the error as we report handled as false, |
| // leave further error handling as the responsibility of the caller. |
| return 0, false, nil |
| } |
| |
| written, handled, err = pollCopyFileRange(&f.pfd, &src.pfd, remain) |
| if lr != nil { |
| lr.N -= written |
| } |
| return written, handled, wrapSyscallError("copy_file_range", err) |
| } |
| |
| // tryLimitedReader tries to assert the io.Reader to io.LimitedReader, it returns the io.LimitedReader, |
| // the underlying io.Reader and the remaining amount of bytes if the assertion succeeds, |
| // otherwise it just returns the original io.Reader and the theoretical unlimited remaining amount of bytes. |
| func tryLimitedReader(r io.Reader) (*io.LimitedReader, io.Reader, int64) { |
| var remain int64 = 1<<63 - 1 // by default, copy until EOF |
| |
| lr, ok := r.(*io.LimitedReader) |
| if !ok { |
| return nil, r, remain |
| } |
| |
| remain = lr.N |
| return lr, lr.R, remain |
| } |