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futex.2: Use syscall(SYS_...); for system calls without a wrapper 

At the same time, document only headers that are required
for calling the function, or those that are specific to the
function:

<unistd.h> is required for the syscall() prototype.
<sys/syscall.h> is required for the syscall name SYS_xxx.
<linux/futex.h> is specific to this syscall.

However, uint32_t is generic enough that it shouldn't be
documented here.  The system_data_types(7) page already documents
it, and is more precise about it.  The same goes for timespec.

As a general rule a man[23] page should document the header that
includes the prototype, and all of the headers that define macros
that should be used with the call.  However, the information about
types should be restricted to system_data_types(7) (and that page
should probably be improved by adding types), except for types
that are very specific to the call.  Otherwise, we're duplicating
info and it's then harder to maintain, and probably outdated in
the future.

Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Alejandro Colomar 2021-05-10 19:55:10 +02:00 committed by Michael Kerrisk
parent 1cf69258ad
commit 0aa385fe25
1 changed files with 11 additions and 10 deletions
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21
man2/futex.2
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@ -25,18 +25,22 @@ futex \- fast user-space locking
.SH SYNOPSIS
.nf
.PP
.B #include <linux/futex.h>
.B #include <stdint.h>
.B #include <sys/time.h>
.BR "#include <linux/futex.h>" " /* Definition of " FUTEX_* " constants */"
.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.PP
.BI "long futex(uint32_t *" uaddr ", int " futex_op ", uint32_t " val ,
.BI " const struct timespec *" timeout , \
.BI "long syscall(SYS_futex, uint32_t *" uaddr ", int " futex_op \
", uint32_t " val ,
.BI " const struct timespec *" timeout , \
" \fR /* or: \fBuint32_t \fIval2\fP */"
.BI " uint32_t *" uaddr2 ", uint32_t " val3 );
.BI " uint32_t *" uaddr2 ", uint32_t " val3 );
.fi
.PP
.IR Note :
There is no glibc wrapper for this system call; see NOTES.
glibc provides no wrapper for
.BR futex (),
necessitating the use of
.BR syscall (2).
.SH DESCRIPTION
The
.BR futex ()
@ -1695,9 +1699,6 @@ and a sixth argument was added in Linux 2.6.7.
.SH CONFORMING TO
This system call is Linux-specific.
.SH NOTES
Glibc does not provide a wrapper for this system call; call it using
.BR syscall (2).
.PP
Several higher-level programming abstractions are implemented via futexes,
including POSIX semaphores and
various POSIX threads synchronization mechanisms