Fix loss of precision for setting timestamps so roundtrip happens properly
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parent
25a1b96537
commit
19668ac18f
4 changed files with 96 additions and 36 deletions
14
chtimes.go
Normal file
14
chtimes.go
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@ -0,0 +1,14 @@
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// Default implementation of Chtimes
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// +build !linux
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package main
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import (
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"os"
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"time"
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)
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func Chtimes(name string, atime time.Time, mtime time.Time) error {
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return os.Chtimes(name, atime, mtime)
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}
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78
chtimes_linux.go
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78
chtimes_linux.go
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@ -0,0 +1,78 @@
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// An implementation of Chtimes which preserves nanosecond precision under linux
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//
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// Should go in standard library, but here for now
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// +build linux
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package main
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import (
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"os"
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"syscall"
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"time"
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"unsafe"
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)
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// COPIED from syscall
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// byteSliceFromString returns a NUL-terminated slice of bytes
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// containing the text of s. If s contains a NUL byte at any
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// location, it returns (nil, EINVAL).
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func byteSliceFromString(s string) ([]byte, error) {
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for i := 0; i < len(s); i++ {
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if s[i] == 0 {
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return nil, syscall.EINVAL
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}
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}
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a := make([]byte, len(s)+1)
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copy(a, s)
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return a, nil
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}
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// COPIED from syscall
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// bytePtrFromString returns a pointer to a NUL-terminated array of
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// bytes containing the text of s. If s contains a NUL byte at any
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// location, it returns (nil, EINVAL).
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func bytePtrFromString(s string) (*byte, error) {
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a, err := byteSliceFromString(s)
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if err != nil {
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return nil, err
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}
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return &a[0], nil
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}
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// COPIED from syscall auto generated code modified from utimes
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func utimensat(dirfd int, path string, times *[2]syscall.Timespec) (err error) {
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var _p0 *byte
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_p0, err = bytePtrFromString(path)
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if err != nil {
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return
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}
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_, _, e1 := syscall.Syscall(syscall.SYS_UTIMENSAT, uintptr(dirfd), uintptr(unsafe.Pointer(_p0)), uintptr(unsafe.Pointer(times)))
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if e1 != 0 {
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err = e1
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}
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return
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}
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// FIXME needs defining properly!
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const AT_FDCWD = -100
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// COPIED from syscall and modified
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//sys utimes(path string, times *[2]Timeval) (err error)
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func Utimensat(dirfd int, path string, ts []syscall.Timespec) (err error) {
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if len(ts) != 2 {
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return syscall.EINVAL
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}
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return utimensat(dirfd, path, (*[2]syscall.Timespec)(unsafe.Pointer(&ts[0])))
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}
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// COPIED from syscall and modified
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func Chtimes(name string, atime time.Time, mtime time.Time) error {
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var utimes [2]syscall.Timespec
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utimes[0] = syscall.NsecToTimespec(atime.UnixNano())
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utimes[1] = syscall.NsecToTimespec(mtime.UnixNano())
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if e := Utimensat(AT_FDCWD, name, utimes[0:]); e != nil {
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return &os.PathError{"chtimes", name, e}
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}
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return nil
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}
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38
notes.txt
38
notes.txt
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@ -48,40 +48,8 @@ Need to make directory objects otherwise can't upload an empty directory
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Make a fs.Errorf and count errors and log them at a different level
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Seem to be able to read stats to ns precision (using struct stat
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defined in asm-generic/stat.h)
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Submit chtimes_linux.go to standard library
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* Can also fix Futime which isn't using the syscall under linux
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* Also for all the *bsd so likely they could be fixed too
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https://www.kernel.org/doc/man-pages/online/pages/man2/stat.2.html
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but only write them to us precision.
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This is confirmed by looking at the source for Chtimes
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func Chtimes(name string, atime time.Time, mtime time.Time) error {
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var utimes [2]syscall.Timeval
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atime_ns := atime.Unix()*1e9 + int64(atime.Nanosecond())
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mtime_ns := mtime.Unix()*1e9 + int64(mtime.Nanosecond())
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utimes[0] = syscall.NsecToTimeval(atime_ns)
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utimes[1] = syscall.NsecToTimeval(mtime_ns)
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if e := syscall.Utimes(name, utimes[0:]); e != nil {
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return &PathError{"chtimes", name, e}
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}
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return nil
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}
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And
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func NsecToTimeval(nsec int64) (tv Timeval) {
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nsec += 999 // round up to microsecond
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tv.Sec = nsec / 1e9
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tv.Usec = nsec % 1e9 / 1e3
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return
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}
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Seems likely Go should be using
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utimensat() and futimens()
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Instead of utimes() - the syscall is defined already
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SYS_UTIMENSAT
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Also for all the *bsd so likely they could be fixed too
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Can also fix Futime which isn't using the syscall under linux
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@ -77,7 +77,7 @@ func (fs *FsObject) md5sum() (string, error) {
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// Sets the modification time of the local fs object
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func (fs *FsObject) SetModTime(modTime time.Time) {
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err := os.Chtimes(fs.path, modTime, modTime)
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err := Chtimes(fs.path, modTime, modTime)
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if err != nil {
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fs.Debugf("Failed to set mtime on file: %s", err)
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}
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