| // 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 poll |
| |
| import ( |
| "internal/syscall/unix" |
| "sync" |
| "syscall" |
| ) |
| |
| func supportCopyFileRange() bool { |
| return isKernelVersionGE53() |
| } |
| |
| var isKernelVersionGE53 = sync.OnceValue(func() bool { |
| major, minor := unix.KernelVersion() |
| // copy_file_range(2) is broken in various ways on kernels older than 5.3, |
| // see https://go.dev/issue/42400 and |
| // https://man7.org/linux/man-pages/man2/copy_file_range.2.html#VERSIONS |
| return major > 5 || (major == 5 && minor >= 3) |
| }) |
| |
| // For best performance, call copy_file_range() with the largest len value |
| // possible. Linux sets up a limitation of data transfer for most of its I/O |
| // system calls, as MAX_RW_COUNT (INT_MAX & PAGE_MASK). This value equals to |
| // the maximum integer value minus a page size that is typically 2^12=4096 bytes. |
| // That is to say, it's the maximum integer value with the lowest 12 bits unset, |
| // which is 0x7ffff000. |
| const maxCopyFileRangeRound = 0x7ffff000 |
| |
| func handleCopyFileRangeErr(err error, copied, written int64) (bool, error) { |
| switch err { |
| case syscall.ENOSYS: |
| // copy_file_range(2) was introduced in Linux 4.5. |
| // Go supports Linux >= 3.2, so the system call |
| // may not be present. |
| // |
| // If we see ENOSYS, we have certainly not transferred |
| // any data, so we can tell the caller that we |
| // couldn't handle the transfer and let them fall |
| // back to more generic code. |
| return false, nil |
| case syscall.EXDEV, syscall.EINVAL, syscall.EIO, syscall.EOPNOTSUPP, syscall.EPERM: |
| // Prior to Linux 5.3, it was not possible to |
| // copy_file_range across file systems. Similarly to |
| // the ENOSYS case above, if we see EXDEV, we have |
| // not transferred any data, and we can let the caller |
| // fall back to generic code. |
| // |
| // As for EINVAL, that is what we see if, for example, |
| // dst or src refer to a pipe rather than a regular |
| // file. This is another case where no data has been |
| // transferred, so we consider it unhandled. |
| // |
| // If src and dst are on CIFS, we can see EIO. |
| // See issue #42334. |
| // |
| // If the file is on NFS, we can see EOPNOTSUPP. |
| // See issue #40731. |
| // |
| // If the process is running inside a Docker container, |
| // we might see EPERM instead of ENOSYS. See issue |
| // #40893. Since EPERM might also be a legitimate error, |
| // don't mark copy_file_range(2) as unsupported. |
| return false, nil |
| case nil: |
| if copied == 0 { |
| // If we did not read any bytes at all, |
| // then this file may be in a file system |
| // where copy_file_range silently fails. |
| // https://lore.kernel.org/linux-fsdevel/20210126233840.GG4626@dread.disaster.area/T/#m05753578c7f7882f6e9ffe01f981bc223edef2b0 |
| if written == 0 { |
| return false, nil |
| } |
| |
| // Otherwise src is at EOF, which means |
| // we are done. |
| } |
| } |
| return true, err |
| } |