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Reorganize mount/unmount code so it is easier to add Darwin-specific implementation

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After these changes, in order to add Darwin bind-mount implementation, one only needs:
* Adjust HasBindMounts definition in mount.go
* Provide implementation in mount_darwin.go

There was no consensus on adding dependency on bindfs, that seems to be the only working solution for bind-mounts on Darwin as of today, in https://github.com/containerd/containerd/pull/8789, that's why the actual implementation is not added in current PR.

As a bonus, Linux FUSE-related code was moved to a separate file and possibly could be reused on FreeBSD, though this needs testing.

Signed-off-by: Marat Radchenko <marat@slonopotamus.org>
This commit is contained in:
Marat Radchenko
2023-07-09 16:34:12 +03:00
parent dacde84372
commit bfc1465a2c
13 changed files with 200 additions and 221 deletions
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87
core/mount/mount_linux.go
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@@ -26,7 +26,6 @@ import (
"runtime"
"strconv"
"strings"
"time"
"github.com/containerd/log"
"github.com/moby/sys/userns"
@@ -274,92 +273,6 @@ func doPrepareIDMappedOverlay(lowerDirs []string, usernsFd int) (tmpLowerDirs []
return tmpLowerDirs, cleanUp, nil
}
// Unmount the provided mount path with the flags
func Unmount(target string, flags int) error {
if err := unmount(target, flags); err != nil && err != unix.EINVAL {
return err
}
return nil
}
// fuseSuperMagic is defined in statfs(2)
const fuseSuperMagic = 0x65735546
func isFUSE(dir string) bool {
var st unix.Statfs_t
if err := unix.Statfs(dir, &st); err != nil {
return false
}
return st.Type == fuseSuperMagic
}
// unmountFUSE attempts to unmount using fusermount/fusermount3 helper binary.
//
// For FUSE mounts, using these helper binaries is preferred, see:
// https://github.com/containerd/containerd/pull/3765#discussion_r342083514
func unmountFUSE(target string) error {
var err error
for _, helperBinary := range []string{"fusermount3", "fusermount"} {
cmd := exec.Command(helperBinary, "-u", target)
err = cmd.Run()
if err == nil {
return nil
}
}
return err
}
func unmount(target string, flags int) error {
if isFUSE(target) {
if err := unmountFUSE(target); err == nil {
return nil
}
}
for i := 0; i < 50; i++ {
if err := unix.Unmount(target, flags); err != nil {
switch err {
case unix.EBUSY:
time.Sleep(50 * time.Millisecond)
continue
default:
return err
}
}
return nil
}
return fmt.Errorf("failed to unmount target %s: %w", target, unix.EBUSY)
}
// UnmountAll repeatedly unmounts the given mount point until there
// are no mounts remaining (EINVAL is returned by mount), which is
// useful for undoing a stack of mounts on the same mount point.
// UnmountAll all is noop when the first argument is an empty string.
// This is done when the containerd client did not specify any rootfs
// mounts (e.g. because the rootfs is managed outside containerd)
// UnmountAll is noop when the mount path does not exist.
func UnmountAll(mount string, flags int) error {
if mount == "" {
return nil
}
if _, err := os.Stat(mount); os.IsNotExist(err) {
return nil
}
for {
if err := unmount(mount, flags); err != nil {
// EINVAL is returned if the target is not a
// mount point, indicating that we are
// done. It can also indicate a few other
// things (such as invalid flags) which we
// unfortunately end up squelching here too.
if err == unix.EINVAL {
return nil
}
return err
}
}
}
// parseMountOptions takes fstab style mount options and parses them for
// use with a standard mount() syscall
func parseMountOptions(options []string) (opt mountOpt) {