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[bpt/emacs.git] / lib / getgroups.c

diff --git a/lib/getgroups.c b/lib/getgroups.c
new file mode 100644 (file)
index 0000000..f9d3623
--- /dev/null
+++ b/lib/getgroups.c
@@ -0,0 +1,116 @@
+/* provide consistent interface to getgroups for systems that don't allow N==0
+
+   Copyright (C) 1996, 1999, 2003, 2006-2012 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* written by Jim Meyering */
+
+#include <config.h>
+
+#include <unistd.h>
+
+#include <errno.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#if !HAVE_GETGROUPS
+
+/* Provide a stub that fails with ENOSYS, since there is no group
+   information available on mingw.  */
+int
+getgroups (int n _GL_UNUSED, GETGROUPS_T *groups _GL_UNUSED)
+{
+  errno = ENOSYS;
+  return -1;
+}
+
+#else /* HAVE_GETGROUPS */
+
+# undef getgroups
+# ifndef GETGROUPS_ZERO_BUG
+#  define GETGROUPS_ZERO_BUG 0
+# endif
+
+/* On at least Ultrix 4.3 and NextStep 3.2, getgroups (0, NULL) always
+   fails.  On other systems, it returns the number of supplemental
+   groups for the process.  This function handles that special case
+   and lets the system-provided function handle all others.  However,
+   it can fail with ENOMEM if memory is tight.  It is unspecified
+   whether the effective group id is included in the list.  */
+
+int
+rpl_getgroups (int n, gid_t *group)
+{
+  int n_groups;
+  GETGROUPS_T *gbuf;
+  int saved_errno;
+
+  if (n < 0)
+    {
+      errno = EINVAL;
+      return -1;
+    }
+
+  if (n != 0 || !GETGROUPS_ZERO_BUG)
+    {
+      int result;
+      if (sizeof *group == sizeof *gbuf)
+        return getgroups (n, (GETGROUPS_T *) group);
+
+      if (SIZE_MAX / sizeof *gbuf <= n)
+        {
+          errno = ENOMEM;
+          return -1;
+        }
+      gbuf = malloc (n * sizeof *gbuf);
+      if (!gbuf)
+        return -1;
+      result = getgroups (n, gbuf);
+      if (0 <= result)
+        {
+          n = result;
+          while (n--)
+            group[n] = gbuf[n];
+        }
+      saved_errno = errno;
+      free (gbuf);
+      errno == saved_errno;
+      return result;
+    }
+
+  n = 20;
+  while (1)
+    {
+      /* No need to worry about address arithmetic overflow here,
+         since the ancient systems that we're running on have low
+         limits on the number of secondary groups.  */
+      gbuf = malloc (n * sizeof *gbuf);
+      if (!gbuf)
+        return -1;
+      n_groups = getgroups (n, gbuf);
+      if (n_groups == -1 ? errno != EINVAL : n_groups < n)
+        break;
+      free (gbuf);
+      n *= 2;
+    }
+
+  saved_errno = errno;
+  free (gbuf);
+  errno = saved_errno;
+
+  return n_groups;
+}
+
+#endif /* HAVE_GETGROUPS */