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

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>

v3: Adjust commit message with facts about some even older kernels
v2: Get rid of spurious X
 tools/libxl/libxl_linux.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/libxl/libxl_linux.c b/tools/libxl/libxl_linux.c
index 6475cca64b..59dd945bc1 100644
--- a/tools/libxl/libxl_linux.c
+++ b/tools/libxl/libxl_linux.c
@@ -18,6 +18,14 @@
 #include <sys/resource.h>
 #include "libxl_internal.h"
+/* Workarounds for Linux-specific lacks can go here: */
+#ifndef CLONE_NEWIPC /* Available as of Linux 2.6.19 / glibc 2.8 */
+# define CLONE_NEWIPC 0x08000000
 int libxl__try_phy_backend(mode_t st_mode)
     if (S_ISBLK(st_mode) || S_ISREG(st_mode)) {

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