Set O_APPEND mode for stdout/stderr and output-sync temporary files.

POSIX does not guarantee that writes will be atomic if a file is
opened for normal (non-append) output.  That means if multiple processes
are writing to the same file, output could be lost.  I can't think of
a real use-case where we would NOT want append for stdout/stderr, so
force it if we can.

4 files changed, 35 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index fe97e4a..b24186a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2013-06-28  Paul Smith  <psmith@gnu.org>
+
+	* misc.c (set_append_mode): Set the O_APPEND flag on a file descriptor.
+	(open_tmpfd): Set append mode on the temporary file descriptor.
+	* main.c (main): Set append mode on stdout and stderr.
+	* makeint.h (set_append_mode): Declare it.
+
 2013-06-22  Eli Zaretskii  <eliz@gnu.org>
 
 	* build_w32.bat (LinkGCC): Prevent a comment from being displayed
@@ -55,7 +62,7 @@
 	* main.c (verify_flag): Global variable to determine whether to
 	verify the database or not.
 	(decode_debug_flags): If debug mode, enable verify_flag.
-	(main): If MAKE_MAINTAINTER_MODE, enable verify_flag, otherwise not.
+	(main): If MAKE_MAINTAINER_MODE, enable verify_flag, otherwise not.
 	(die): Only verify the database if verify_flag is set.
 	* file.c (enter_file): Don't check caching unless verify_flag.
 	* makeint.h: Export verify_flag.
diff --git a/main.c b/main.c
index fe8d355..83a95db 100644
--- a/main.c
+++ b/main.c
@@ -1195,6 +1195,12 @@ main (int argc, char **argv, char **envp)
   setlinebuf (stdout);
 #endif  /* setlinebuf missing.  */
 
+  /* Configure stdout/stderr to be in append mode.
+     This keeps parallel jobs from losing output due to overlapping writes.  */
+
+  set_append_mode (fileno (stdout));
+  set_append_mode (fileno (stderr));
+
   /* Figure out where this program lives.  */
 
   if (argv[0] == 0)
diff --git a/makeint.h b/makeint.h
index f119680..b51e914 100644
--- a/makeint.h
+++ b/makeint.h
@@ -453,6 +453,7 @@ int alpha_compare (const void *, const void *);
 void print_spaces (unsigned int);
 char *find_percent (char *);
 const char *find_percent_cached (const char **);
+void set_append_mode (int);
 int open_tmpfd (void);
 FILE *open_tmpfile (char **, const char *);
 
diff --git a/misc.c b/misc.c
index 1b1441b..d3a1da5 100644
--- a/misc.c
+++ b/misc.c
@@ -22,6 +22,11 @@ this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <stdarg.h>
 
+#ifdef HAVE_FCNTL_H
+# include <fcntl.h>
+#else
+# include <sys/file.h>
+#endif
 
 /* Compare strings *S1 and *S2.
    Return negative if the first is less, positive if it is greater,
@@ -897,6 +902,19 @@ get_path_max (void)
 #endif
 
 
+/* Set a file descriptor to be in O_APPEND mode.
+   If it fails, just ignore it.  */
+
+void
+set_append_mode (int fd)
+{
+#if defined(F_GETFL) && defined(F_SETFL) && defined(O_APPEND)
+  int flags = fcntl (fd, F_GETFL, 0);
+  if (flags >= 0)
+    fcntl (fd, F_SETFL, flags | O_APPEND);
+#endif
+}
+
 /* Provide support for temporary files.  */
 
 #ifndef HAVE_STDLIB_H
@@ -928,6 +946,8 @@ open_tmpfd ()
 
   fclose (tfile);
 
+  set_append_mode (fd);
+
   return fd;
 }