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daemon: kernelSupportsRecursivelyReadOnly: use sync.OnceValue

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Use a sync.OnceValue for recursive read-only mount detection to simplify
the kernel feature detection. Also remove the temporary directory after
the mount is unmounted to avoid leaving it behind.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
This commit is contained in:
Sebastiaan van Stijn committed 2026-11-02 13:04:47 +01:00
1 parent 71b1b4b34d
commit a306fac8a6
1 file changed
+41 -51
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daemon/daemon_linux.go
+41 -51
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@@ -168,59 +168,49 @@ func ifaceAddrs(linkName string, family int) ([]netlink.Addr, error) {
return nl.AddrList(link, family)
}
var (
kernelSupportsRROOnce sync.Once
kernelSupportsRROErr error
)
func kernelSupportsRecursivelyReadOnly() error {
fn := func() error {
tmpMnt, err := os.MkdirTemp("", "moby-detect-rro")
if err != nil {
return fmt.Errorf("failed to create a temp directory: %w", err)
}
for {
err = unix.Mount("", tmpMnt, "tmpfs", 0, "")
if !errors.Is(err, unix.EINTR) {
break
}
}
if err != nil {
return fmt.Errorf("failed to mount tmpfs on %q: %w", tmpMnt, err)
}
defer func() {
var umErr error
for {
umErr = unix.Unmount(tmpMnt, 0)
if !errors.Is(umErr, unix.EINTR) {
break
}
}
if umErr != nil {
log.G(context.TODO()).WithError(umErr).Warnf("Failed to unmount %q", tmpMnt)
}
}()
attr := &unix.MountAttr{
Attr_set: unix.MOUNT_ATTR_RDONLY,
}
for {
err = unix.MountSetattr(-1, tmpMnt, unix.AT_RECURSIVE, attr)
if !errors.Is(err, unix.EINTR) {
break
}
}
// ENOSYS on kernel < 5.12
if err != nil {
return fmt.Errorf("failed to call mount_setattr: %w", err)
}
return nil
var kernelSupportsRecursivelyReadOnly = sync.OnceValue(func() error {
tmpMnt, err := os.MkdirTemp("", "moby-detect-rro")
if err != nil {
return fmt.Errorf("failed to create a temp directory: %w", err)
}
defer func() { _ = os.Remove(tmpMnt) }()
kernelSupportsRROOnce.Do(func() {
kernelSupportsRROErr = fn()
})
return kernelSupportsRROErr
}
for {
err = unix.Mount("", tmpMnt, "tmpfs", 0, "")
if !errors.Is(err, unix.EINTR) {
break
}
}
if err != nil {
return fmt.Errorf("failed to mount tmpfs on %q: %w", tmpMnt, err)
}
defer func() {
var umErr error
for {
umErr = unix.Unmount(tmpMnt, 0)
if !errors.Is(umErr, unix.EINTR) {
break
}
}
if umErr != nil {
log.G(context.TODO()).WithError(umErr).Warnf("Failed to unmount %q", tmpMnt)
}
}()
attr := &unix.MountAttr{
Attr_set: unix.MOUNT_ATTR_RDONLY,
}
for {
err = unix.MountSetattr(-1, tmpMnt, unix.AT_RECURSIVE, attr)
if !errors.Is(err, unix.EINTR) {
break
}
}
// ENOSYS on kernel < 5.12
if err != nil {
return fmt.Errorf("failed to call mount_setattr: %w", err)
}
return nil
})
func supportsRecursivelyReadOnly(cfg *configStore, runtime string) error {
if err := kernelSupportsRecursivelyReadOnly(); err != nil {