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The C and C++ Include Header Files

cat -n /usr/include/x86_64-linux-gnu/bits/ipc-perm.h

     1	/* struct ipc_perm definition.
     2	   Copyright (C) 2019-2026 Free Software Foundation, Inc.
     3	   This file is part of the GNU C Library.
     4	
     5	   The GNU C Library is free software; you can redistribute it and/or
     6	   modify it under the terms of the GNU Lesser General Public
     7	   License as published by the Free Software Foundation; either
     8	   version 2.1 of the License, or (at your option) any later version.
     9	
    10	   The GNU C Library is distributed in the hope that it will be useful,
    11	   but WITHOUT ANY WARRANTY; without even the implied warranty of
    12	   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    13	   Lesser General Public License for more details.
    14	
    15	   You should have received a copy of the GNU Lesser General Public
    16	   License along with the GNU C Library; if not, see
    17	   <http://www.gnu.org/licenses/>.  */
    18	
    19	#ifndef _SYS_IPC_H
    20	# error "Never use <bits/ipc-perm.h> directly; include <sys/ipc.h> instead."
    21	#endif
    22	
    23	/* Data structure used to pass permission information to IPC operations.
    24	   It follows the kernel ipc64_perm size so the syscall can be made directly
    25	   without temporary buffer copy.  However, since glibc defines the MODE
    26	   field as mode_t per POSIX definition (BZ#18231), it omits the __PAD1 field
    27	   (since glibc does not export mode_t as 16-bit for any architecture).  */
    28	struct ipc_perm
    29	{
    30	  __key_t __key;				/* Key.  */
    31	  __uid_t uid;					/* Owner's user ID.  */
    32	  __gid_t gid;					/* Owner's group ID.  */
    33	  __uid_t cuid;					/* Creator's user ID.  */
    34	  __gid_t cgid;					/* Creator's group ID.  */
    35	  __mode_t mode;				/* Read/write permission.  */
    36	  unsigned short int __seq;			/* Sequence number.  */
    37	  unsigned short int __pad2;
    38	  __syscall_ulong_t __glibc_reserved1;
    39	  __syscall_ulong_t __glibc_reserved2;
    40	};