forked from rosa/hakurei
ext: wrap file-descriptor-based mount facilities
This only implements what is required by package container for now. Signed-off-by: Ophestra <cat@gensokyo.uk>
This commit is contained in:
267
ext/fs.go
Normal file
267
ext/fs.go
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@@ -0,0 +1,267 @@
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package ext
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import (
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"os"
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"runtime"
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"syscall"
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"unsafe"
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)
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// include/uapi/linux/mount.h
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/*
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* move_mount() flags.
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*/
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const (
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MOVE_MOUNT_F_SYMLINKS = 1 << iota /* Follow symlinks on from path */
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MOVE_MOUNT_F_AUTOMOUNTS /* Follow automounts on from path */
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MOVE_MOUNT_F_EMPTY_PATH /* Empty from path permitted */
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_
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MOVE_MOUNT_T_SYMLINKS /* Follow symlinks on to path */
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MOVE_MOUNT_T_AUTOMOUNTS /* Follow automounts on to path */
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MOVE_MOUNT_T_EMPTY_PATH /* Empty to path permitted */
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_
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MOVE_MOUNT_SET_GROUP /* Set sharing group instead */
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MOVE_MOUNT_BENEATH /* Mount beneath top mount */
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)
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/*
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* fsopen() flags.
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*/
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const (
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FSOPEN_CLOEXEC = 1 << iota
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)
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/*
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* fspick() flags.
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*/
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const (
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FSPICK_CLOEXEC = 1 << iota
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FSPICK_SYMLINK_NOFOLLOW
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FSPICK_NO_AUTOMOUNT
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FSPICK_EMPTY_PATH
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)
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/*
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* The type of fsconfig() call made.
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*/
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const (
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FSCONFIG_SET_FLAG = iota /* Set parameter, supplying no value */
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FSCONFIG_SET_STRING /* Set parameter, supplying a string value */
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FSCONFIG_SET_BINARY /* Set parameter, supplying a binary blob value */
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FSCONFIG_SET_PATH /* Set parameter, supplying an object by path */
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FSCONFIG_SET_PATH_EMPTY /* Set parameter, supplying an object by (empty) path */
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FSCONFIG_SET_FD /* Set parameter, supplying an object by fd */
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FSCONFIG_CMD_CREATE /* Create new or reuse existing superblock */
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FSCONFIG_CMD_RECONFIGURE /* Invoke superblock reconfiguration */
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FSCONFIG_CMD_CREATE_EXCL /* Create new superblock, fail if reusing existing superblock */
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)
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/*
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* fsmount() flags.
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*/
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const (
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FSMOUNT_CLOEXEC = 1 << iota
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)
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/*
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* Mount attributes.
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*/
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const (
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MOUNT_ATTR_RDONLY = 0x00000001 /* Mount read-only */
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MOUNT_ATTR_NOSUID = 0x00000002 /* Ignore suid and sgid bits */
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MOUNT_ATTR_NODEV = 0x00000004 /* Disallow access to device special files */
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MOUNT_ATTR_NOEXEC = 0x00000008 /* Disallow program execution */
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MOUNT_ATTR__ATIME = 0x00000070 /* Setting on how atime should be updated */
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MOUNT_ATTR_RELATIME = 0x00000000 /* - Update atime relative to mtime/ctime. */
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MOUNT_ATTR_NOATIME = 0x00000010 /* - Do not update access times. */
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MOUNT_ATTR_STRICTATIME = 0x00000020 /* - Always perform atime updates */
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MOUNT_ATTR_NODIRATIME = 0x00000080 /* Do not update directory access times */
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MOUNT_ATTR_IDMAP = 0x00100000 /* Idmap mount to @userns_fd in struct mount_attr. */
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MOUNT_ATTR_NOSYMFOLLOW = 0x00200000 /* Do not follow symlinks */
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)
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// FS provides low-level wrappers around the suite of file-descriptor-based
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// mount facilities in Linux.
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type FS struct {
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fd uintptr
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c runtime.Cleanup
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}
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// newFS allocates a new [FS] for the specified fd.
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func newFS(fd uintptr) *FS {
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fs := FS{fd: fd}
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fs.c = runtime.AddCleanup(&fs, func(fd uintptr) {
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_ = syscall.Close(int(fd))
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}, fd)
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return &fs
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}
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// Close closes the underlying filesystem context.
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func (fs *FS) Close() error {
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if fs == nil {
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return syscall.EINVAL
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}
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err := syscall.Close(int(fs.fd))
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fs.c.Stop()
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return err
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}
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// OpenFS creates a new filesystem context.
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func OpenFS(fsname string, flags int) (fs *FS, err error) {
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var s *byte
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s, err = syscall.BytePtrFromString(fsname)
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if err != nil {
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return
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}
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fd, _, errno := syscall.Syscall(
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SYS_FSOPEN,
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uintptr(unsafe.Pointer(s)),
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uintptr(flags|FSOPEN_CLOEXEC),
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0,
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)
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if errno != 0 {
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err = os.NewSyscallError("fsopen", errno)
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} else {
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fs = newFS(fd)
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}
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return
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}
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// PickFS selects filesystem for reconfiguration.
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func PickFS(dirfd int, pathname string, flags int) (fs *FS, err error) {
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var s *byte
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s, err = syscall.BytePtrFromString(pathname)
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if err != nil {
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return
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}
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fd, _, errno := syscall.Syscall(
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SYS_FSPICK,
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uintptr(dirfd),
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uintptr(unsafe.Pointer(s)),
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uintptr(flags|FSPICK_CLOEXEC),
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)
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if errno != 0 {
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err = os.NewSyscallError("fspick", errno)
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} else {
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fs = newFS(fd)
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}
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return
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}
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// config configures new or existing filesystem context.
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func (fs *FS) config(cmd uint, key *byte, value unsafe.Pointer, aux int) (err error) {
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_, _, errno := syscall.Syscall6(
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SYS_FSCONFIG,
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fs.fd,
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uintptr(cmd),
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uintptr(unsafe.Pointer(key)),
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uintptr(value),
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uintptr(aux),
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0,
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)
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if errno != 0 {
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err = os.NewSyscallError("fsconfig", errno)
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}
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return
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}
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// SetFlag sets the flag parameter named by key. ([FSCONFIG_SET_FLAG])
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func (fs *FS) SetFlag(key string) (err error) {
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var s *byte
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s, err = syscall.BytePtrFromString(key)
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if err != nil {
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return
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}
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return fs.config(FSCONFIG_SET_FLAG, s, nil, 0)
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}
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// SetString sets the string parameter named by key to the value specified by
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// value. ([FSCONFIG_SET_STRING])
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func (fs *FS) SetString(key, value string) (err error) {
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var s0 *byte
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s0, err = syscall.BytePtrFromString(key)
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if err != nil {
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return
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}
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var s1 *byte
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s1, err = syscall.BytePtrFromString(value)
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if err != nil {
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return
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}
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return fs.config(FSCONFIG_SET_STRING, s0, unsafe.Pointer(s1), 0)
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}
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// mount instantiates mount object from filesystem context.
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func (fs *FS) mount(flags, attrFlags int) (fsfd int, err error) {
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r, _, errno := syscall.Syscall(
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SYS_FSMOUNT,
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fs.fd,
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uintptr(flags|FSMOUNT_CLOEXEC),
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uintptr(attrFlags),
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)
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fsfd = int(r)
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if errno != 0 {
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err = os.NewSyscallError("fsmount", errno)
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}
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return
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}
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// MoveMount moves or attaches mount object to filesystem.
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func MoveMount(
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fromDirfd int,
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fromPathname string,
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toDirfd int,
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toPathname string,
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flags int,
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) (err error) {
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var s0 *byte
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s0, err = syscall.BytePtrFromString(fromPathname)
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if err != nil {
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return
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}
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var s1 *byte
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s1, err = syscall.BytePtrFromString(toPathname)
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if err != nil {
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return
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}
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_, _, errno := syscall.Syscall6(
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SYS_MOVE_MOUNT,
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uintptr(fromDirfd),
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uintptr(unsafe.Pointer(s0)),
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uintptr(toDirfd),
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uintptr(unsafe.Pointer(s1)),
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uintptr(flags),
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0,
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)
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if errno != 0 {
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err = os.NewSyscallError("move_mount", errno)
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}
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return
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}
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// Mount attaches the underlying filesystem context to the specified pathname.
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func (fs *FS) Mount(pathname string, attrFlags int) error {
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if err := fs.config(FSCONFIG_CMD_CREATE_EXCL, nil, nil, 0); err != nil {
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return err
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}
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fd, err := fs.mount(0, attrFlags)
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if err != nil {
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return err
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}
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err = MoveMount(
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fd, "",
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-1, pathname,
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MOVE_MOUNT_F_EMPTY_PATH,
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)
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closeErr := syscall.Close(fd)
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if err == nil {
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err = closeErr
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}
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return err
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}
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