Re: [Xen-devel] [PATCH v3 3/3] libxl: fix build (missing CLONE_NEWIPC) on astonishingly old systems

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Jan 14, 2019 at 02:59:37PM +0000, Ian Jackson 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.
> 
> 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 by anything except some pre-2.6.18
> kernels.  On those kernels we do not want to support dm_restrict, and
> an attempt to use it will fail.  It is OK for the failure to be a
> messy EINVAL syscall failure.  (The IPC namespace unshare is necessary
> to avoid a suborned deprivileged qemu from causing trouble with shm,
> sem, etc.)
> 
> On the very old kernels, the feature is totally out of scope.
> (We are only interested, here, in making the build work, to avoid
> blocking people who aren't using this feature.)
> 
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Juergen Gross <jgross@xxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> 

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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