[libvirt] [PATCH] virprocess: Extend list of platforms for setns wrapper

[Michal Privoznik]

On 15.09.2014 17:32, Martin Kletzander wrote:
> On Mon, Sep 15, 2014 at 04:22:18PM +0100, Daniel P. Berrange wrote:
>> On Mon, Sep 15, 2014 at 05:20:46PM +0200, Michal Privoznik wrote:
>>> On 15.09.2014 17:15, Martin Kletzander wrote:
>>> >On Mon, Sep 15, 2014 at 03:43:55PM +0200, Michal Privoznik wrote:
>>> >>Currently, the setns() wrapper is supported only for x86_64 and i686
>>> >>which leaves us failing to build on other platforms like arm, aarch64
>>> >>and so on. This means, that the wrapper needs to be extended to those
>>> >>platforms and make to fail on runtime not compile time.
>>> >>
>>> >>The syscall numbers for other platforms was fetched using this
>>> >>command:
>>> >>
>>> >>kernel.git $ git grep "define.*__NR_setns" | grep -e arm -e powerpc -e
>>> >>s390
>>> >>arch/arm/include/uapi/asm/unistd.h:#define
>>> >>__NR_setns                   (__NR_SYSCALL_BASE+375)
>>> >>arch/arm64/include/asm/unistd32.h:#define __NR_setns 375
>>> >>arch/powerpc/include/uapi/asm/unistd.h:#define
>>> >>__NR_setns               350
>>> >>arch/s390/include/uapi/asm/unistd.h:#define __NR_setns          339
>>> >>
>>> >>Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>>> >>---
>>> >>src/util/virprocess.c | 18 ++++++++++++------
>>> >>1 file changed, 12 insertions(+), 6 deletions(-)
>>> >>
>>> >
>>> >NACK, we shouldn't be duplicating syscall definitions.  There should
>>> >be AC_CHECK_FUNCS([setns]) (instead of AC_CHECK_FUNCS_ONCE() for the
>>> >syscall) and having with_lxc = "yes" and ac_cv_func_setns != "yes"
>>> >should result in an error.
>>>
>>> The only problem with this might be that on systems with older glibc
>>> (and
>>> there is plenty of them) libvirt will fail to build / miss this
>>> feature. And
>>> it's not that the kernel doesn't support the namesapces. But let me
>>> see if I
>>> can get some ACKs on that approach you're suggesting.
>>
>> That's basically what the code did before we added the #define or
>> NR_setns.
>> We took the patch specifically to help Debian where the kernel has it but
>> glibc is outdated.
>>
>
> Either Debian should patch their glibc or we should at lease use
> SYS_setns IMHO.

That's not gonna fly either. On my system, the SYS_setns is declared in:

# grep -r SYS_setns /usr/include/
/usr/include/bits/syscall.h:#define SYS_setns __NR_setns

And the syscall.h belongs to glibc, not kernel headers. So we are back 
at the start.

Michal