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# -*- Autoconf -*-
# SYNOPSIS
#
# AX_CHECK_USER_NAMESPACE
#
# DESCRIPTION
#
# This macro checks whether the local system supports Linux user namespaces.
# If so, it calls AC_DEFINE(HAVE_USER_NAMESPACE).
AC_DEFUN([AX_CHECK_USER_NAMESPACE],[dnl
AC_CACHE_CHECK([whether user namespaces are supported],
ax_cv_user_namespace,[
AC_LANG_PUSH([C])
AC_RUN_IFELSE([AC_LANG_SOURCE([[
#define _GNU_SOURCE
#include <fcntl.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
int userfn(void *d) {
usleep(100000); /* synchronize by sleep */
return (getuid() != 0);
}
char userst[1024*1024];
int main() {
char buffer[1024];
int rc, status, fd;
pid_t child = clone(userfn, userst + 1024*1024, CLONE_NEWUSER|SIGCHLD, 0);
if (child < 0) return 1;
sprintf(buffer, "/proc/%d/uid_map", child);
fd = open(buffer, O_CREAT|O_WRONLY|O_TRUNC, 0755);
sprintf(buffer, "0 %d 1\n", getuid());
write(fd, buffer, strlen(buffer));
close(fd);
rc = waitpid(child, &status, 0);
if (rc <= 0) return 1;
if (!WIFEXITED(status)) return 1;
return WEXITSTATUS(status);
}
]])],[ax_cv_user_namespace=yes],[ax_cv_user_namespace=no],[ax_cv_user_namespace=no])
AC_LANG_POP([C])
])
if test "$ax_cv_user_namespace" = yes; then
AC_DEFINE([HAVE_USER_NAMESPACE],[1],[Whether user namespaces are available])
fi
]) # AX_CHECK_USER_NAMESPACE
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