253 lines
7.1 KiB
Go
253 lines
7.1 KiB
Go
package sysfs
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import (
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"io/fs"
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"os"
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"syscall"
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"time"
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"github.com/tetratelabs/wazero/internal/platform"
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)
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// NewReadFS is used to mask an existing FS for reads. Notably, this allows
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// the CLI to do read-only mounts of directories the host user can write, but
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// doesn't want the guest wasm to. For example, Python libraries shouldn't be
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// written to at runtime by the python wasm file.
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func NewReadFS(fs FS) FS {
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if _, ok := fs.(*readFS); ok {
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return fs
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} else if _, ok = fs.(UnimplementedFS); ok {
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return fs // unimplemented is read-only
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}
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return &readFS{fs: fs}
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}
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type readFS struct {
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fs FS
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}
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// String implements fmt.Stringer
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func (r *readFS) String() string {
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return r.fs.String()
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}
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// OpenFile implements FS.OpenFile
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func (r *readFS) OpenFile(path string, flag int, perm fs.FileMode) (platform.File, syscall.Errno) {
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// TODO: Once the real implementation is complete, move the below to
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// /RATIONALE.md. Doing this while the type is unstable creates
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// documentation drift as we expect a lot of reshaping meanwhile.
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//
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// Callers of this function expect to either open a valid file handle, or
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// get an error, if they can't. We want to return ENOSYS if opened for
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// anything except reads.
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//
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// Instead, we could return a fake no-op file on O_WRONLY. However, this
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// hurts observability because a later write error to that file will be on
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// a different source code line than the root cause which is opening with
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// an unsupported flag.
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//
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// The tricky part is os.RD_ONLY is typically defined as zero, so while the
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// parameter is named flag, the part about opening read vs write isn't a
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// typical bitflag. We can't compare against zero anyway, because even if
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// there isn't a current flag to OR in with that, there may be in the
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// future. What we do instead is mask the flags about read/write mode and
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// check if they are the opposite of read or not.
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switch flag & (os.O_RDONLY | os.O_WRONLY | os.O_RDWR) {
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case os.O_WRONLY, os.O_RDWR:
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return nil, syscall.ENOSYS
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default: // os.O_RDONLY so we are ok!
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}
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f, errno := r.fs.OpenFile(path, flag, perm)
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if errno != 0 {
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return nil, errno
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}
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return &readFile{f: f}, 0
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}
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// compile-time check to ensure readFile implements platform.File.
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var _ platform.File = (*readFile)(nil)
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type readFile struct {
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f platform.File
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}
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// Path implements the same method as documented on platform.File.
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func (r *readFile) Path() string {
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return r.f.Path()
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}
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// AccessMode implements the same method as documented on platform.File.
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func (r *readFile) AccessMode() int {
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return r.f.AccessMode()
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}
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// IsNonblock implements the same method as documented on platform.File.
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func (r *readFile) IsNonblock() bool {
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return r.f.IsNonblock()
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}
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// SetNonblock implements the same method as documented on platform.File.
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func (r *readFile) SetNonblock(enabled bool) syscall.Errno {
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return r.f.SetNonblock(enabled)
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}
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// Stat implements the same method as documented on platform.File.
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func (r *readFile) Stat() (platform.Stat_t, syscall.Errno) {
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return r.f.Stat()
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}
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// IsDir implements the same method as documented on platform.File.
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func (r *readFile) IsDir() (bool, syscall.Errno) {
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return r.f.IsDir()
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}
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// Read implements the same method as documented on platform.File.
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func (r *readFile) Read(buf []byte) (int, syscall.Errno) {
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return r.f.Read(buf)
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}
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// Pread implements the same method as documented on platform.File.
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func (r *readFile) Pread(buf []byte, offset int64) (int, syscall.Errno) {
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return r.f.Pread(buf, offset)
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}
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// Seek implements the same method as documented on platform.File.
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func (r *readFile) Seek(offset int64, whence int) (int64, syscall.Errno) {
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return r.f.Seek(offset, whence)
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}
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// Readdir implements the same method as documented on platform.File.
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func (r *readFile) Readdir(n int) (dirents []platform.Dirent, errno syscall.Errno) {
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return r.f.Readdir(n)
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}
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// Write implements the same method as documented on platform.File.
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func (r *readFile) Write([]byte) (int, syscall.Errno) {
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return 0, r.writeErr()
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}
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// Pwrite implements the same method as documented on platform.File.
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func (r *readFile) Pwrite([]byte, int64) (n int, errno syscall.Errno) {
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return 0, r.writeErr()
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}
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// Truncate implements the same method as documented on platform.File.
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func (r *readFile) Truncate(int64) syscall.Errno {
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return r.writeErr()
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}
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// Sync implements the same method as documented on platform.File.
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func (r *readFile) Sync() syscall.Errno {
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return syscall.EBADF
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}
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// Datasync implements the same method as documented on platform.File.
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func (r *readFile) Datasync() syscall.Errno {
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return syscall.EBADF
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}
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// Chmod implements the same method as documented on platform.File.
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func (r *readFile) Chmod(fs.FileMode) syscall.Errno {
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return syscall.EBADF
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}
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// Chown implements the same method as documented on platform.File.
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func (r *readFile) Chown(int, int) syscall.Errno {
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return syscall.EBADF
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}
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// Utimens implements the same method as documented on platform.File.
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func (r *readFile) Utimens(*[2]syscall.Timespec) syscall.Errno {
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return syscall.EBADF
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}
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func (r *readFile) writeErr() syscall.Errno {
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if isDir, errno := r.IsDir(); errno != 0 {
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return errno
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} else if isDir {
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return syscall.EISDIR
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}
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return syscall.EBADF
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}
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// Close implements the same method as documented on platform.File.
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func (r *readFile) Close() syscall.Errno {
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return r.f.Close()
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}
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// PollRead implements File.PollRead
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func (r *readFile) PollRead(timeout *time.Duration) (ready bool, errno syscall.Errno) {
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return r.f.PollRead(timeout)
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}
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// Lstat implements FS.Lstat
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func (r *readFS) Lstat(path string) (platform.Stat_t, syscall.Errno) {
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return r.fs.Lstat(path)
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}
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// Stat implements FS.Stat
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func (r *readFS) Stat(path string) (platform.Stat_t, syscall.Errno) {
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return r.fs.Stat(path)
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}
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// Readlink implements FS.Readlink
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func (r *readFS) Readlink(path string) (dst string, err syscall.Errno) {
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return r.fs.Readlink(path)
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}
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// Mkdir implements FS.Mkdir
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func (r *readFS) Mkdir(path string, perm fs.FileMode) syscall.Errno {
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return syscall.EROFS
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}
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// Chmod implements FS.Chmod
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func (r *readFS) Chmod(path string, perm fs.FileMode) syscall.Errno {
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return syscall.EROFS
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}
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// Chown implements FS.Chown
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func (r *readFS) Chown(path string, uid, gid int) syscall.Errno {
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return syscall.EROFS
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}
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// Lchown implements FS.Lchown
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func (r *readFS) Lchown(path string, uid, gid int) syscall.Errno {
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return syscall.EROFS
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}
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// Rename implements FS.Rename
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func (r *readFS) Rename(from, to string) syscall.Errno {
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return syscall.EROFS
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}
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// Rmdir implements FS.Rmdir
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func (r *readFS) Rmdir(path string) syscall.Errno {
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return syscall.EROFS
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}
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// Link implements FS.Link
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func (r *readFS) Link(_, _ string) syscall.Errno {
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return syscall.EROFS
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}
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// Symlink implements FS.Symlink
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func (r *readFS) Symlink(_, _ string) syscall.Errno {
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return syscall.EROFS
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}
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// Unlink implements FS.Unlink
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func (r *readFS) Unlink(path string) syscall.Errno {
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return syscall.EROFS
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}
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// Utimens implements FS.Utimens
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func (r *readFS) Utimens(path string, times *[2]syscall.Timespec, symlinkFollow bool) syscall.Errno {
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return syscall.EROFS
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}
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// Truncate implements FS.Truncate
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func (r *readFS) Truncate(string, int64) syscall.Errno {
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return syscall.EROFS
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}
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