svn commit: r357614 - in head/sys: kern sys

Conrad Meyer cem at freebsd.org
Thu Feb 6 16:37:05 UTC 2020


Hi Pawel,

I don't think the (notyet) static assertion is quite right.

On Thu, Feb 6, 2020 at 4:46 AM Pawel Biernacki <kaktus at freebsd.org> wrote:
>
> Author: kaktus
> Date: Thu Feb  6 12:45:58 2020
> New Revision: 357614
> URL: https://svnweb.freebsd.org/changeset/base/357614
>
> Log:
>   sysctl(9): add CTLFLAG_NEEDGIANT flag
> ...
> Modified: head/sys/sys/sysctl.h
> ==============================================================================
> --- head/sys/sys/sysctl.h       Thu Feb  6 10:11:41 2020        (r357613)
> +++ head/sys/sys/sysctl.h       Thu Feb  6 12:45:58 2020        (r357614)
> @@ -105,6 +105,13 @@ struct ctlname {
> ...
> + * One, and only one of CTLFLAG_MPSAFE or CTLFLAG_NEEDGIANT is required
> + * for SYSCTL_PROC and SYSCTL_NODE.
> ...
> @@ -263,6 +270,14 @@ TAILQ_HEAD(sysctl_ctx_list, sysctl_ctx_entry);
>  #define        __DESCR(d) ""
>  #endif
>
> +#ifdef notyet
> +#define        SYSCTL_ENFORCE_FLAGS(x)                                         \
> +    _Static_assert(((CTLFLAG_MPSAFE ^ CTLFLAG_NEEDGIANT) & (x)),       \
> +        "Has to be either CTLFLAG_MPSAFE or CTLFLAG_NEEDGIANT")

The current (notyet) assertion checks for one or both flags being set,
but you want to disallow both being set.  The XOR operator here is
meaningless; it is the same as OR for different bit flags.

That would be something like:

#define _CTLFLAG_MUTUALLY_EXCLUSIVE    (CTLFLAG_MPSAFE | CTLFLAG_NEEDGIANT);
#define SYSCTL_ENFORCE_FLAGS(x)  do { \
        _Static_assert(((x) & _CTLFLAG_MUTUALLY_EXCLUSIVE) != 0 && \
            ((x) & _CTLFLAG_MUTUALLY_EXCLUSIVE) !=
_CTLFLAG_MUTUALLY_EXCLUSIVE, \
            "Must set exactly one of CTLFLAG_MPSAFE, CTLFLAG_NEEDGIANT"); \
} while (0)

Best,
Conrad


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