freebsd-dev/lib/libc/sys/getgroups.2
Brooks Davis 54404cfb13 In preparation for raising NGROUPS and NGROUPS_MAX, change base
system callers of getgroups(), getgrouplist(), and setgroups() to
allocate buffers dynamically.  Specifically, allocate a buffer of size
sysconf(_SC_NGROUPS_MAX)+1 (+2 in a few cases to allow for overflow).

This (or similar gymnastics) is required for the code to actually follow
the POSIX.1-2008 specification where {NGROUPS_MAX} may differ at runtime
and where getgroups may return {NGROUPS_MAX}+1 results on systems like
FreeBSD which include the primary group.

In id(1), don't pointlessly add the primary group to the list of all
groups, it is always the first result from getgroups().  In principle
the old code was more portable, but this was only done in one of the two
places where getgroups() was called to the overall effect was pointless.

Document the actual POSIX requirements in the getgroups(2) and
setgroups(2) manpages.  We do not yet support a dynamic NGROUPS, but we
may in the future.

MFC after:	2 weeks
2009-06-19 15:58:24 +00:00

102 lines
3.0 KiB
Groff

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.\" @(#)getgroups.2 8.2 (Berkeley) 4/16/94
.\" $FreeBSD$
.\"
.Dd March 5, 1999
.Dt GETGROUPS 2
.Os
.Sh NAME
.Nm getgroups
.Nd get group access list
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In unistd.h
.Ft int
.Fn getgroups "int gidsetlen" "gid_t *gidset"
.Sh DESCRIPTION
The
.Fn getgroups
system call
gets the current group access list of the user process
and stores it in the array
.Fa gidset .
The
.Fa gidsetlen
argument
indicates the number of entries that may be placed in
.Fa gidset .
The
.Fn getgroups
system call
returns the actual number of groups returned in
.Fa gidset .
At least one and as many as {NGROUPS_MAX}+1 values may be returned.
If
.Fa gidsetlen
is zero,
.Fn getgroups
returns the number of supplementary group IDs associated with
the calling process without modifying the array pointed to by
.Fa gidset .
.Sh RETURN VALUES
A successful call returns the number of groups in the group set.
A value of -1 indicates that an error occurred, and the error
code is stored in the global variable
.Va errno .
.Sh ERRORS
The possible errors for
.Fn getgroups
are:
.Bl -tag -width Er
.It Bq Er EINVAL
The argument
.Fa gidsetlen
is smaller than the number of groups in the group set.
.It Bq Er EFAULT
The argument
.Fa gidset
specifies
an invalid address.
.El
.Sh SEE ALSO
.Xr setgroups 2 ,
.Xr initgroups 3
.Sh STANDARDS
The
.Fn getgroups
system call conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn getgroups
system call appeared in
.Bx 4.2 .