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      1 /*
      2  * Find out the size of kernel's sigset_t.
      3  *
      4  * Copyright (c) 2016-2017 Dmitry V. Levin <ldv (at) altlinux.org>
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  * 3. The name of the author may not be used to endorse or promote products
     16  *    derived from this software without specific prior written permission.
     17  *
     18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     19  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     20  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     21  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     22  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     23  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     24  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     25  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     26  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     27  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     28  */
     29 
     30 #include "tests.h"
     31 #include <signal.h>
     32 #include <unistd.h>
     33 #include <asm/unistd.h>
     34 
     35 /*
     36  * If the sigset size specified to rt_sigprocmask is not equal to the size
     37  * of kernel's sigset_t, the kernel does not look at anything else and fails
     38  * with EINVAL.
     39  *
     40  * Otherwise, if both pointers specified to rt_sigprocmask are NULL,
     41  * the kernel just returns 0.
     42  *
     43  * This vaguely documented kernel feature can be used to probe
     44  * the kernel and find out the size of kernel's sigset_t.
     45  */
     46 
     47 unsigned int
     48 get_sigset_size(void)
     49 {
     50 	static unsigned int set_size;
     51 
     52 	if (!set_size) {
     53 		static const unsigned int big_size = 1024 / 8;
     54 
     55 		for (set_size = big_size; set_size; set_size >>= 1) {
     56 			if (!syscall(__NR_rt_sigprocmask, SIG_SETMASK,
     57 				     NULL, NULL, set_size))
     58 				break;
     59 		}
     60 
     61 		if (!set_size)
     62 			perror_msg_and_fail("rt_sigprocmask");
     63 	}
     64 
     65 	return set_size;
     66 }
     67