From 814e597c4ed49ca59b8f24a5f16a487409a4804e Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Fri, 17 Jul 2020 12:35:59 +0100
Subject: [PATCH] lib/utils.c: Use strerrordesc_np as alternative in async-safe
 perror.

See:
https://lists.fedoraproject.org/archives/list/glibc@lists.fedoraproject.org/thread/WJHGG2OO7ABNAYICGA5WQZ2Q34Q2FEHU/

Thanks: Florian Weimer
---
 configure.ac |  5 +++++
 lib/utils.c  | 31 +++++++++++++++++++------------
 2 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/configure.ac b/configure.ac
index e5c29cd..a44e3b1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -79,6 +79,11 @@ AC_CHECK_HEADERS([\
 
 AC_CHECK_HEADERS([linux/vm_sockets.h], [], [], [#include <sys/socket.h>])
 
+dnl Check for strerrordesc_np (optional, glibc only).
+dnl Prefer this over sys_errlist.
+dnl https://lists.fedoraproject.org/archives/list/glibc@lists.fedoraproject.org/thread/WJHGG2OO7ABNAYICGA5WQZ2Q34Q2FEHU/
+AC_CHECK_FUNCS([strerrordesc_np])
+
 dnl Check for sys_errlist (optional).
 AC_MSG_CHECKING([for sys_errlist])
 AC_TRY_LINK([], [extern int sys_errlist; char *p = &sys_errlist;], [
diff --git a/lib/utils.c b/lib/utils.c
index bc62f93..86e9849 100644
--- a/lib/utils.c
+++ b/lib/utils.c
@@ -136,6 +136,11 @@ nbd_internal_fork_safe_itoa (long v, char *buf, size_t bufsize)
   return &buf[i];
 }
 
+#if defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-result"
+#endif
+
 /* Fork-safe version of perror.  ONLY use this after fork and before
  * exec, the rest of the time use set_error().
  */
@@ -143,24 +148,22 @@ void
 nbd_internal_fork_safe_perror (const char *s)
 {
   const int err = errno;
+  const char *m = NULL;
+  char buf[32];
 
-#if defined(__GNUC__)
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wunused-result"
-#endif
   write (2, s, strlen (s));
   write (2, ": ", 2);
-#if HAVE_SYS_ERRLIST
-  write (2, sys_errlist[errno], strlen (sys_errlist[errno]));
+#ifdef HAVE_STRERRORDESC_NP
+  m = strerrordesc_np (errno);
 #else
-  char buf[32];
-  const char *v = nbd_internal_fork_safe_itoa ((long) errno, buf, sizeof buf);
-  write (2, v, strlen (v));
+#ifdef HAVE_SYS_ERRLIST
+  m = errno >= 0 && errno < sys_nerr ? sys_errlist[errno] : NULL;
 #endif
+#endif
+  if (!m)
+    m = nbd_internal_fork_safe_itoa ((long) errno, buf, sizeof buf);
+  write (2, m, strlen (m));
   write (2, "\n", 1);
-#if defined(__GNUC__)
-#pragma GCC diagnostic pop
-#endif
 
   /* Restore original errno in case it was disturbed by the system
    * calls above.
@@ -168,6 +171,10 @@ nbd_internal_fork_safe_perror (const char *s)
   errno = err;
 }
 
+#if defined(__GNUC__)
+#pragma GCC diagnostic pop
+#endif
+
 /* nbd_internal_printable_* functions are used by the API code to
  * print debug messages when we trace calls in and out of libnbd.  The
  * calls should attempt to convert the parameter into something
-- 
2.27.0