Re: Syscalls: eventfd and timerfd

On Tue, Jan 10, 2023 at 5:39 PM Rob Wing <rob.fx907@gmail.com> wrote:

> You might also be interested in checking out Brooks Davis' talk on adding
> syscalls:
>
>
> https://www.bsdcan.org/events/bsdcan_2022/sessions/session/73/slides/35/so-you-want-to-add-a-syscall.pdf
>
> https://youtu.be/_5LF_0GIpi8
>

I must've missed this when trying to find documentation on this topic.
Thanks for recommending this. I'll give it a watch.

Jake Freeland


>
>
> On Tuesday, January 10, 2023, Mateusz Guzik <mjguzik@gmail.com> wrote:
>
>> It is added with a non-standard entry point.
>>
>> If you git log -p sys/kern/sys_eventfd.c you will see:
>>
>> commit 7a202823aa54ba18c485bdbcf355269bcfee1ab9
>> Author: Konstantin Belousov <kib@FreeBSD.org>
>> Date:   Wed Dec 23 16:14:04 2020 +0200
>>
>>     Expose eventfd in the native API/ABI using a new __specialfd syscall
>>
>> then if you git grep __specialfd:
>> lib/libc/gen/eventfd.c: return (__sys___specialfd(SPECIALFD_EVENTFD,
>> &args, sizeof(args)));
>> lib/libc/include/libc_private.h:int             __sys___specialfd(int,
>> const void *, __size_t);
>> sys/compat/freebsd32/freebsd32_syscall.h:#define
>> FREEBSD32_SYS___specialfd       577
>> sys/compat/freebsd32/freebsd32_syscalls.c:      "__specialfd",
>>          /* 577 = __specialfd */
>> sys/compat/freebsd32/freebsd32_sysent.c:        { .sy_narg =
>> AS(__specialfd_args), .sy_call = (sy_call_t *)sys___specialfd,
>> .sy_auevent = AUE_SPECIALFD, .sy_flags = SYF_CAPENABLED, .sy_thrcnt =
>> SY_THR_STATIC },    /* 577 = __specialfd */
>> sys/compat/freebsd32/freebsd32_systrace_args.c: /* __specialfd */
>> sys/compat/freebsd32/freebsd32_systrace_args.c:         struct
>> __specialfd_args *p = params;
>> sys/compat/freebsd32/freebsd32_systrace_args.c: /* __specialfd */
>> sys/compat/freebsd32/freebsd32_systrace_args.c: /* __specialfd */
>> sys/kern/init_sysent.c: { .sy_narg = AS(__specialfd_args), .sy_call =
>> (sy_call_t *)sys___specialfd, .sy_auevent = AUE_SPECIALFD, .sy_flags =
>> SYF_CAPENABLED, .sy_thrcnt = SY_THR_STATIC },    /* 577 = __specialfd
>> */
>> sys/kern/sys_generic.c:sys___specialfd(struct thread *td, struct
>> __specialfd_args *args)
>> sys/kern/syscalls.c:    "__specialfd",                  /* 577 =
>> __specialfd */
>> sys/kern/syscalls.master:               int __specialfd(
>> sys/kern/systrace_args.c:       /* __specialfd */
>> sys/kern/systrace_args.c:               struct __specialfd_args *p =
>> params;
>> sys/kern/systrace_args.c:       /* __specialfd */
>> sys/kern/systrace_args.c:       /* __specialfd */
>> sys/sys/syscall.h:#define       SYS___specialfd 577
>> sys/sys/syscall.mk:     __specialfd.o \
>> sys/sys/sysproto.h:struct __specialfd_args {
>> sys/sys/sysproto.h:int  sys___specialfd(struct thread *, struct
>> __specialfd_args *);
>> sys/sys/sysproto.h:#define      SYS_AUE___specialfd     AUE_SPECIALFD
>>
>> On 1/11/23, Jake Freeland <jake@technologyfriends.net> wrote:
>> > Hi there,
>> >
>> > I am currently working on moving the linux_compat implementation of
>> > timerfd (in sys/compat/linux/linux_event.c) into its own FreeBSD syscall
>> > similar to what was done for eventfd. This is my first time implementing
>> > a syscall, so I have been following the eventfd implementation as a
>> > reference. I noticed that the eventfd syscall entries are absent from
>> > sys/kern/syscalls.master and I am not sure why. Was eventfd never
>> > formally added as a syscall entry or am I missing something? I was
>> > planning on adding timerfd entries to syscalls.master, but now I am
>> > unsure how to proceed.
>> >
>> > I apologize for my ignorance. This process is new to me.
>> >
>> > Thank you,
>> > Jake Freeland
>> >
>>
>>
>> --
>> Mateusz Guzik <mjguzik gmail.com>
>>
>>