Re: [Xen-devel] [PATCH] libxl: fix build on rather old systems

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jan 11, 2019 at 12:06:59PM +0000, George Dunlap wrote:
> 
> 
> > On Jan 11, 2019, at 9:18 PM, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> > 
> > On Fri, Jan 11, 2019 at 03:09:35AM -0700, Jan Beulich wrote:
> >> CLONE_NEWIPC has been introduced in Linux 2.6.19 only (and into glibc
> >> at around that time as well). Cope with it being undefined as well as
> >> with the underlying kernel not knowing of it.
> >> 
> >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> >> ---
> >> Considering how old "old" here really means, I could understand if
> >> this was rejected, in which case I'd carry a simplified version locally.
> >> I don't run such old kernels together with modern Xen, but I do
> >> occasionally build on such old systems.
> 
> But why do you build on it if you don’t run it?
> 

It isn't uncommon to have separate build setup. But I guess haven't a
rather old build setup but run the software on a newer setup is
uncommon.

> >> 
> >> --- a/tools/libxl/libxl_linux.c
> >> +++ b/tools/libxl/libxl_linux.c
> >> @@ -334,12 +334,24 @@ int libxl__local_dm_preexec_restrict(lib
> >>     unsigned i;
> >> 
> >>     /* Unshare mount and IPC namespaces.  These are unused by QEMU. */
> >> -    r = unshare(CLONE_NEWNS | CLONE_NEWIPC);
> >> +    r = unshare(CLONE_NEWNS);
> >>     if (r) {
> >> -        LOGE(ERROR, "libxl: Mount and IPC namespace unfailed");
> >> +        LOGE(ERROR, "libxl: Mount namespace unshare failed");
> >>         return ERROR_FAIL;
> >>     }
> >> 
> >> +#ifndef CLONE_NEWIPC /* Available as of Linux 2.6.19 / glibc 2.8 */
> >> +# define CLONE_NEWIPC 0x08000000
> > 
> > I have no problem making it build with this.
> > 
> >> +#endif
> >> +    r = unshare(CLONE_NEWIPC);
> >> +    if (r) {
> >> +        if (r && errno != EINVAL) {
> >> +            LOGE(ERROR, "libxl: IPC namespace unshare failed");
> >> +            return ERROR_FAIL;
> >> +        }
> >> +        LOG(WARN, "libxl: IPC namespace unshare unavailable");
> > 
> > But I guess whether it should be allowed to continue or not is another
> > question. Do we consider this IPC namespace "must-have”?
> 
> On the contrary, the mount and IPC namespaces are “might-as-well” (or 
> perhaps, “why-not-it-cant-hurt”).
> 
> I don’t really see any point making something build on a system that you’re 
> not going to run it on; but I don’t feel strongly enough to do more than say 
> so.  I’ll leave it up to the toolstack maintainers.

Fine then. I interpret this as "IPC namespace is not a must-have".
I think Jan's patch is fine. I will have a closer look in the afternoon.

Wei.

> 
>  -George

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