On Fri, Mar 20, 2020 at 11:33:55AM -0700, Andrei Vagin wrote:
> On Thu, Mar 19, 2020 at 11:29:55AM +0100, Christian Brauner wrote:
> > On Thu, Mar 19, 2020 at 09:16:43AM +0100, Arnd Bergmann wrote:
> > > On Thu, Mar 19, 2020 at 9:11 AM Adrian Reber <areber@xxxxxxxxxx> wrote:
> > >
> > > > With Arnd's idea of only using nanoseconds, timens_offset would then
> > > > contain something like this:
> > > >
> > > > struct timens_offset {
> > > > __aligned_s64 monotonic_offset_ns;
> > > > __aligned_s64 boottime_offset_ns;
> > > > };
> > > >
> > > > I kind of prefer adding boottime and monotonic directly to struct clone_args
> > > >
> > > > __aligned_u64 tls;
> > > > __aligned_u64 set_tid;
> > > > __aligned_u64 set_tid_size;
> > > > + __aligned_s64 monotonic_offset_ns;
> > > > + __aligned_s64 boottime_offset_ns;
> > > > };
> > >
> > > I would also prefer the second approach using two 64-bit integers
> > > instead of a pointer, as it keeps the interface simpler to implement
> > > and simpler to interpret by other tools.
> >
> > Why I don't like has two reasons. There's the scenario where we have
> > added new extensions after the new boottime member and then we introduce
> > another offset. Then you'd be looking at:
> >
> > __aligned_u64 tls;
> > __aligned_u64 set_tid;
> > __aligned_u64 set_tid_size;
> > + __aligned_s64 monotonic_offset_ns;
> > + __aligned_s64 boottime_offset_ns;
> > __aligned_s64 something_1
> > __aligned_s64 anything_2
> > + __aligned_s64 sometime_offset_ns
> >
> > which bothers me just by looking at it. That's in addition to adding two
> > new members to the struct when most people will never set CLONE_NEWTIME.
> > We'll also likely have more features in the future that will want to
> > pass down more info than we want to directly expose in struct
> > clone_args, e.g. for a long time I have been thinking about adding a
> > struct for CLONE_NEWUSER that allows you to specify the id mappings you
> > want the new user namespace to get. We surely don't want to force all
> > new info into the uppermost struct. So I'm not convinced we should here.
>
> I think here we can start thinking about a netlink-like interface.
I think netlink is just not a great model for an API and I would not
want us to go down that route.
I kept thinking about this for a bit and I think that we will end up
growing more namespace-related functionality. So one thing that came to
my mind is the following layout:
struct {
struct {
__s64 monotonic;
__s64 boot;
} time;
} namespaces;
struct _clone_args {
__aligned_u64 flags;
__aligned_u64 pidfd;
__aligned_u64 child_tid;
__aligned_u64 parent_tid;
__aligned_u64 exit_signal;
__aligned_u64 stack;
__aligned_u64 stack_size;
__aligned_u64 tls;
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 namespaces;
__aligned_u64 namespaces_size;
};
Then when we end up adding id mapping support for CLONE_NEWUSER we can
extend this with:
struct {
struct {
__aligned_u64 monotonic;
__aligned_u64 boot;
} time;
struct {
/* id mapping members */
} user;
} namespaces;
Thoughts? Other ideas?
Christian
