Merge "overlayfs: Use userxattrs on supporting kernels."

const auto kLowerdirOption = "lowerdir="s;

const auto kUpperdirOption = "upperdir="s;

static inline bool KernelSupportsUserXattrs() {

    struct utsname uts;

    uname(&uts);

    int major, minor;

    if (sscanf(uts.release, "%d.%d", &major, &minor) != 2) {

        return false;

    }

    return major > 5 || (major == 5 && minor >= 15);

}

// default options for mount_point, returns empty string for none available.

std::string fs_mgr_get_overlayfs_options(const std::string& mount_point) {

    auto candidate = fs_mgr_get_overlayfs_candidate(mount_point);

    if (fs_mgr_overlayfs_valid() == OverlayfsValidResult::kOverrideCredsRequired) {

        ret += ",override_creds=off";

    }

    if (KernelSupportsUserXattrs()) {

        ret += ",userxattr";

    }

    return ret;

}