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@@ -131,3 +131,106 @@ func IsAbs(path string) bool {
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}
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return true
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}
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+
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+// The origin of the functions below here are the golang OS and syscall packages,
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+// slightly modified to only cope with files, not directories due to the
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+// specific use case.
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+//
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+// The alteration is to allow a file on Windows to be opened with
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+// FILE_FLAG_SEQUENTIAL_SCAN (particular for docker load), to avoid eating
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+// the standby list, particularly when accessing large files such as layer.tar.
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+
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+// CreateSequential creates the named file with mode 0666 (before umask), truncating
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+// it if it already exists. If successful, methods on the returned
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+// File can be used for I/O; the associated file descriptor has mode
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+// O_RDWR.
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+// If there is an error, it will be of type *PathError.
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+func CreateSequential(name string) (*os.File, error) {
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+ return OpenFileSequential(name, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0)
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+}
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+
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+// OpenSequential opens the named file for reading. If successful, methods on
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+// the returned file can be used for reading; the associated file
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+// descriptor has mode O_RDONLY.
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+// If there is an error, it will be of type *PathError.
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+func OpenSequential(name string) (*os.File, error) {
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+ return OpenFileSequential(name, os.O_RDONLY, 0)
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+}
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+
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+// OpenFileSequential is the generalized open call; most users will use Open
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+// or Create instead.
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+// If there is an error, it will be of type *PathError.
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+func OpenFileSequential(name string, flag int, _ os.FileMode) (*os.File, error) {
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+ if name == "" {
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+ return nil, &os.PathError{"open", name, syscall.ENOENT}
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+ }
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+ r, errf := syscallOpenFileSequential(name, flag, 0)
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+ if errf == nil {
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+ return r, nil
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+ }
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+ return nil, &os.PathError{"open", name, errf}
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+}
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+
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+func syscallOpenFileSequential(name string, flag int, _ os.FileMode) (file *os.File, err error) {
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+ r, e := syscallOpenSequential(name, flag|syscall.O_CLOEXEC, 0)
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+ if e != nil {
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+ return nil, e
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+ }
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+ return os.NewFile(uintptr(r), name), nil
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+}
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+
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+func makeInheritSa() *syscall.SecurityAttributes {
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+ var sa syscall.SecurityAttributes
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+ sa.Length = uint32(unsafe.Sizeof(sa))
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+ sa.InheritHandle = 1
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+ return &sa
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+}
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+
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+func syscallOpenSequential(path string, mode int, _ uint32) (fd syscall.Handle, err error) {
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+ if len(path) == 0 {
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+ return syscall.InvalidHandle, syscall.ERROR_FILE_NOT_FOUND
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+ }
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+ pathp, err := syscall.UTF16PtrFromString(path)
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+ if err != nil {
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+ return syscall.InvalidHandle, err
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+ }
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+ var access uint32
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+ switch mode & (syscall.O_RDONLY | syscall.O_WRONLY | syscall.O_RDWR) {
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+ case syscall.O_RDONLY:
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+ access = syscall.GENERIC_READ
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+ case syscall.O_WRONLY:
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+ access = syscall.GENERIC_WRITE
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+ case syscall.O_RDWR:
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+ access = syscall.GENERIC_READ | syscall.GENERIC_WRITE
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+ }
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+ if mode&syscall.O_CREAT != 0 {
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+ access |= syscall.GENERIC_WRITE
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+ }
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+ if mode&syscall.O_APPEND != 0 {
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+ access &^= syscall.GENERIC_WRITE
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+ access |= syscall.FILE_APPEND_DATA
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+ }
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+ sharemode := uint32(syscall.FILE_SHARE_READ | syscall.FILE_SHARE_WRITE)
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+ var sa *syscall.SecurityAttributes
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+ if mode&syscall.O_CLOEXEC == 0 {
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+ sa = makeInheritSa()
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+ }
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+ var createmode uint32
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+ switch {
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+ case mode&(syscall.O_CREAT|syscall.O_EXCL) == (syscall.O_CREAT | syscall.O_EXCL):
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+ createmode = syscall.CREATE_NEW
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+ case mode&(syscall.O_CREAT|syscall.O_TRUNC) == (syscall.O_CREAT | syscall.O_TRUNC):
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+ createmode = syscall.CREATE_ALWAYS
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+ case mode&syscall.O_CREAT == syscall.O_CREAT:
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+ createmode = syscall.OPEN_ALWAYS
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+ case mode&syscall.O_TRUNC == syscall.O_TRUNC:
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+ createmode = syscall.TRUNCATE_EXISTING
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+ default:
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+ createmode = syscall.OPEN_EXISTING
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+ }
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+ // Use FILE_FLAG_SEQUENTIAL_SCAN rather than FILE_ATTRIBUTE_NORMAL as implemented in golang.
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+ //https://msdn.microsoft.com/en-us/library/windows/desktop/aa363858(v=vs.85).aspx
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+ const fileFlagSequentialScan = 0x08000000 // FILE_FLAG_SEQUENTIAL_SCAN
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+ h, e := syscall.CreateFile(pathp, access, sharemode, sa, createmode, fileFlagSequentialScan, 0)
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+ return h, e
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+}
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