Re: [Xen-devel] [PATCH v2 2/2] libxl: fix build (missing CLONE_NEWIPC) on astonishingly old systems

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Jan 14, 2019 at 02:47:58AM -0700, Jan Beulich wrote:
> >>> On 11.01.19 at 20:23, <ian.jackson@xxxxxxxxxxxxx> wrote:
> > CLONE_NEWIPC was introduced in Linux 2.6.19, on the 29th of November
> > 2006, which was 12 years, 1 month, and 14 days ago.
> 
> Thanks for the very precise counting, the latter part which will be
> wrong - even if just slightly - by the time you commit it ;-)
> 
> > Nevertheless apparently some people are trying to build Xen on systems
> > whose kernel headers are that old.  Placate these people by providing
> > a fallback #define for CLONE_NEWIPC.
> > 
> > The actual binary value will of course remain constant, because of the
> > kernel API promise, so this is and will be correct on all platforms
> > where the CLONE_NEWIPC is supported.  (Even if for some reason we miss
> > the right #includes.)
> > 
> > Of course at runtime this value will not work on older kernels.  It
> > will be rejected as unknown.
> 
> Sadly the situation is more complicated: The check to disallow
> unknown flags was introduced only in 2.6.17 [1], and apparently
> never backported to 2.6.16 or older stable trees despite the
> description talking about it going into 2.6.16. Since it didn't
> matter in my variant of the workaround, I didn't mention this.
> 
> Of course a pretty reasonable position to take would be to
> consider the 2.6.18-based XenoLinux tree a "baseline", beyond
> which we don't care about undesirable behavior here.

I think using 2.6.18 as baseline is very reasonable. 

Wei.

> 
> Jan
> 
> [1] 06f9d4f94a unshare: Error if passed unsupported flags
> 
> 

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