Re: git: ba0d9b43e940 - main - kern_descrip.c: provide helpers to translate between fd flags namespace
Date: Sat, 12 Jul 2025 17:07:28 UTC
On 7/11/25 15:00, Konstantin Belousov wrote:
> On Fri, Jul 11, 2025 at 11:46:33AM -0400, John Baldwin wrote:
>> On 7/8/25 17:49, Konstantin Belousov wrote:
>>> The branch main has been updated by kib:
>>>
>>> URL: https://cgit.FreeBSD.org/src/commit/?id=ba0d9b43e940077f4025e7e4e85d16c8d525db79
>>>
>>> commit ba0d9b43e940077f4025e7e4e85d16c8d525db79
>>> Author: Konstantin Belousov <kib@FreeBSD.org>
>>> AuthorDate: 2025-07-08 16:30:29 +0000
>>> Commit: Konstantin Belousov <kib@FreeBSD.org>
>>> CommitDate: 2025-07-08 21:48:59 +0000
>>>
>>> kern_descrip.c: provide helpers to translate between fd flags namespace
>>> Reviewed by: markj
>>> Sponsored by: The FreeBSD Foundation
>>> Differential revision: https://reviews.freebsd.org/D51206
>>> ---
>>> sys/kern/kern_descrip.c | 110 +++++++++++++++++++++++++++++++++++++++---------
>>> 1 file changed, 90 insertions(+), 20 deletions(-)
>>>
>>> diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
>>> index 406236fc2723..2e1da2fdee29 100644
>>> --- a/sys/kern/kern_descrip.c
>>> +++ b/sys/kern/kern_descrip.c
>>> @@ -480,6 +480,90 @@ kern_fcntl_freebsd(struct thread *td, int fd, int cmd, intptr_t arg)
>>> return (error);
>>> }
>>> +struct flags_trans_elem {
>>> + u_int f;
>>> + u_int t;
>>> +};
>>> +
>>> +static u_int
>>> +flags_trans(const struct flags_trans_elem *ftes, int nitems, u_int from_flags)
>>> +{
>>> + u_int res;
>>> + int i;
>>> +
>>> + res = 0;
>>> + for (i = 0; i < nitems; i++) {
>>> + if ((from_flags & ftes[i].f) != 0)
>>> + res |= ftes[i].t;
>>> + }
>>> + return (res);
>>> +}
>>> +
>>> +static uint8_t
>>> +fd_to_fde_flags(int fd_flags)
>>> +{
>>> + static const struct flags_trans_elem fd_to_fde_flags_s[] = {
>>> + { .f = FD_CLOEXEC, .t = UF_EXCLOSE },
>>> + { .f = FD_CLOFORK, .t = UF_FOCLOSE },
>>> + { .f = FD_RESOLVE_BENEATH, .t = UF_RESOLVE_BENEATH },
>>> + };
>>> +
>>> + return (flags_trans(fd_to_fde_flags_s, nitems(fd_to_fde_flags_s),
>>> + fd_flags));
>>> +}
>>> +
>>> +static int
>>> +fde_to_fd_flags(uint8_t fde_flags)
>>> +{
>>> + static const struct flags_trans_elem fde_to_fd_flags_s[] = {
>>> + { .f = UF_EXCLOSE, .t = FD_CLOEXEC },
>>> + { .f = UF_FOCLOSE, .t = FD_CLOFORK },
>>> + { .f = UF_RESOLVE_BENEATH, .t = FD_RESOLVE_BENEATH },
>>> + };
>>> +
>>> + return (flags_trans(fde_to_fd_flags_s, nitems(fde_to_fd_flags_s),
>>> + fde_flags));
>>> +}
>>> +
>>> +static uint8_t
>>> +fddup_to_fde_flags(int fddup_flags)
>>> +{
>>> + static const struct flags_trans_elem fddup_to_fde_flags_s[] = {
>>> + { .f = FDDUP_FLAG_CLOEXEC, .t = UF_EXCLOSE },
>>> + { .f = FDDUP_FLAG_CLOFORK, .t = UF_FOCLOSE },
>>> + };
>>> +
>>> + return (flags_trans(fddup_to_fde_flags_s, nitems(fddup_to_fde_flags_s),
>>> + fddup_flags));
>>> +}
>>> +
>>> +static uint8_t
>>> +close_range_to_fde_flags(int close_range_flags)
>>> +{
>>> + static const struct flags_trans_elem close_range_to_fde_flags_s[] = {
>>> + { .f = CLOSE_RANGE_CLOEXEC, .t = UF_EXCLOSE },
>>> + { .f = CLOSE_RANGE_CLOFORK, .t = UF_FOCLOSE },
>>> + };
>>> +
>>> + return (flags_trans(close_range_to_fde_flags_s,
>>> + nitems(close_range_to_fde_flags_s), close_range_flags));
>>> +}
>>> +
>>> +static uint8_t
>>> +open_to_fde_flags(int open_flags, bool sticky_orb)
>>> +{
>>> + static const struct flags_trans_elem open_to_fde_flags_s[] = {
>>> + { .f = O_CLOEXEC, .t = UF_EXCLOSE },
>>> + { .f = O_CLOFORK, .t = UF_FOCLOSE },
>>> + { .f = O_RESOLVE_BENEATH, .t = UF_RESOLVE_BENEATH },
>>> + };
>>> + _Static_assert(open_to_fde_flags_s[nitems(open_to_fde_flags_s) - 1].f ==
>>> + O_RESOLVE_BENEATH, "O_RESOLVE_BENEATH must be last, for sticky_orb");
>>
>> This broke the GCC builds it seems. GCC doesn't think that it can compute this
>> expression at compile time.
>>
>> From https://ci.freebsd.org/job/FreeBSD-main-amd64-gcc14_build/1022/console:
>>
>> 10:32:02 /workspace/src/sys/kern/kern_descrip.c: In function 'open_to_fde_flags':
>> 10:32:02 /workspace/src/sys/kern/kern_descrip.c:560:79: error: expression in static =
>> 10:32:02 assertion is not constant
>> 10:32:02 560 | _Static_assert(open_to_fde_flags_s[nitems(open_to_fde_flags=
>> 10:32:02 _s) - 1].f =3D=3D
>>
>
> I am unable to propose anything better than the patch below. We have enough
> #ifdef __clang__ in non-contrib sources already, so this should be not a
> huge crime?
>
> % rg -g '!contrib/*' __clang__ | wc -l
> 171
>
> commit 96e6b15b0a1407af45ebe1ad38ee53627d09d16b
> Author: Konstantin Belousov <kib@FreeBSD.org>
> Date: Fri Jul 11 21:57:32 2025 +0300
>
> kern_descrip.c: only allow complex expression in Static_assert() for clang
>
> gcc cannot compute the assert expression.
>
> Reported by: jhb
>
> diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
> index 93bdd41d1515..c4f5e586b0ed 100644
> --- a/sys/kern/kern_descrip.c
> +++ b/sys/kern/kern_descrip.c
> @@ -557,8 +557,10 @@ open_to_fde_flags(int open_flags, bool sticky_orb)
> { .f = O_CLOFORK, .t = UF_FOCLOSE },
> { .f = O_RESOLVE_BENEATH, .t = UF_RESOLVE_BENEATH },
> };
> +#ifdef __clang__
> _Static_assert(open_to_fde_flags_s[nitems(open_to_fde_flags_s) - 1].f ==
> O_RESOLVE_BENEATH, "O_RESOLVE_BENEATH must be last, for sticky_orb");
> +#endif
I think this is fine. Mark Millard followed up with me offline and it may be that
GCC is technically more correct here with what is allowed to be computed as a static
constant at compile time FWIW. C++' constexpr allows for a wider range of
compile-time constant values compared to C and this sort of thing feels very
constexpr-like.
--
John Baldwin