Hi Hauke,
On Sun, Feb 14, 2021 at 06:09:40PM +0100, Hauke Mehrtens wrote:
> Musl libc does not define the glibc specific macro __GLIBC_PREREQ(), but
> it has the clock_adjtime() function. Assume that a libc implementation
> which does not define __GLIBC_PREREQ at all still implements
> clock_adjtime().
>
> This fixes a build problem with musl libc because the __GLIBC_PREREQ()
> macro is missing.
>
> Fixes: 42e1358e103d ("ptp: In the testptp utility, use clock_adjtime from glibc when available")
> Signed-off-by: Hauke Mehrtens <hauke@xxxxxxxxxx>
> ---
> tools/testing/selftests/ptp/testptp.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/tools/testing/selftests/ptp/testptp.c b/tools/testing/selftests/ptp/testptp.c
> index f7911aaeb007..ecffe2c78543 100644
> --- a/tools/testing/selftests/ptp/testptp.c
> +++ b/tools/testing/selftests/ptp/testptp.c
> @@ -38,6 +38,7 @@
> #define NSEC_PER_SEC 1000000000LL
>
> /* clock_adjtime is not available in GLIBC < 2.14 */
> +#ifdef __GLIBC_PREREQ
> #if !__GLIBC_PREREQ(2, 14)
> #include <sys/syscall.h>
> static int clock_adjtime(clockid_t id, struct timex *tx)
> @@ -45,6 +46,7 @@ static int clock_adjtime(clockid_t id, struct timex *tx)
> return syscall(__NR_clock_adjtime, id, tx);
> }
> #endif
> +#endif /* __GLIBC_PREREQ */
I guess this works, but as you say, there is still an assumption to be
made there, which is that all other C libraries provide the clock_adjtime
syscall definition. So it is likely that this set of #if's and #ifdef's
will be revisited again and again and ...
Maybe this is a matter of personal preference, but I wonder if it's not
actually preferable to do something like this?
#include <sys/syscall.h>
static int compat_clock_adjtime(clockid_t id, struct timex *tx)
{
return syscall(__NR_clock_adjtime, id, tx);
}
#define clock_adjtime compat_clock_adjtime
This way, everybody uses the same definition of clock_adjtime, and we
bypass the definition provided by libc if there is one, and we provide
our own if there is none.
