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package mountopts
import (
"golang.org/x/sys/unix"
)
// UnprivilegedMountFlags gets the set of mount flags that are set on the mount that contains the given
// path and are locked by CL_UNPRIVILEGED. This is necessary to ensure that
// bind-mounting "with options" will not fail with user namespaces, due to
// kernel restrictions that require user namespace mounts to preserve
// CL_UNPRIVILEGED locked flags.
//
// TODO: Move to github.com/moby/sys/mount, and update BuildKit copy of this code as well (https://github.com/moby/buildkit/blob/v0.13.0/util/rootless/mountopts/mountopts_linux.go#L11-L18)
func UnprivilegedMountFlags(path string) ([]string, error) {
var statfs unix.Statfs_t
if err := unix.Statfs(path, &statfs); err != nil {
return nil, err
}
// The set of keys come from https://github.com/torvalds/linux/blob/v4.13/fs/namespace.c#L1034-L1048.
unprivilegedFlags := map[uint64]string{
unix.MS_RDONLY: "ro",
unix.MS_NODEV: "nodev",
unix.MS_NOEXEC: "noexec",
unix.MS_NOSUID: "nosuid",
unix.MS_NOATIME: "noatime",
unix.MS_RELATIME: "relatime",
unix.MS_NODIRATIME: "nodiratime",
}
var flags []string
for mask, flag := range unprivilegedFlags {
if uint64(statfs.Flags)&mask == mask {
flags = append(flags, flag)
}
}
return flags, nil
}
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