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

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> 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?

>> 
>> --- 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.

 -George
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