gdb: convert linux-namespaces debug to the new(er) debug scheme

Convert 'set debug linux-namespaces' to the new(er) debug scheme.  As
part of this change I converted the mnsh_debug_print_message function,
which previously printed its output, to instead return a std::string,
this string is then printed using linux_namespaces_debug_printf.  The
mnsh_debug_print_message function is only used as part of the debug
output.

I also updated one place in the code where debug_linux_namespaces, the
debug control variable, which is a boolean, was assigned an integer.

When debug is turned on then clearly the output is now different, but
in all other cases, there should be no user visible change in GDB
after this commit.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/nat/linux-namespaces.c

@@ -265,62 +265,65 @@ enum mnsh_msg_type
     MNSH_RET_INTSTR,
   };
 
-/* Print a string representation of a message using debug_printf.
-   This function is not async-signal-safe so should never be
-   called from the helper.  */
+/* Return a string representation of a message.  This function is not
+   async-signal-safe so should never be called from the helper.  */
 
-static void
+static std::string
 mnsh_debug_print_message (enum mnsh_msg_type type,
 			  int fd, int int1, int int2,
 			  const void *buf, int bufsiz)
 {
+  std::string res;
+
   gdb_byte *c = (gdb_byte *) buf;
   gdb_byte *cl = c + bufsiz;
 
   switch (type)
     {
     case MNSH_MSG_ERROR:
-      debug_printf ("ERROR");
+      res += "ERROR";
       break;
 
     case MNSH_REQ_SETNS:
-      debug_printf ("SETNS");
+      res += "SETNS";
       break;
 
     case MNSH_REQ_OPEN:
-      debug_printf ("OPEN");
+      res += "OPEN";
       break;
 
     case MNSH_REQ_UNLINK:
-      debug_printf ("UNLINK");
+      res += "UNLINK";
       break;
 
     case MNSH_REQ_READLINK:
-      debug_printf ("READLINK");
+      res += "READLINK";
       break;
 
     case MNSH_RET_INT:
-      debug_printf ("INT");
+      res += "INT";
       break;
 
     case MNSH_RET_FD:
-      debug_printf ("FD");
+      res += "FD";
       break;
 
     case MNSH_RET_INTSTR:
-      debug_printf ("INTSTR");
+      res += "INTSTR";
       break;
 
     default:
-      debug_printf ("unknown-packet-%d", type);
+      res += string_printf ("unknown-packet-%d", type);
     }
 
-  debug_printf (" %d %d %d \"", fd, int1, int2);
+  res += string_printf (" %d %d %d \"", fd, int1, int2);
 
   for (; c < cl; c++)
-    debug_printf (*c >= ' ' && *c <= '~' ? "%c" : "\\%o", *c);
+    res += string_printf (*c >= ' ' && *c <= '~' ? "%c" : "\\%o", *c);
 
-  debug_printf ("\"");
+  res += "\"";
+
+  return res;
 }
 
 /* Forward declaration.  */
@@ -390,12 +393,10 @@ mnsh_send_message (int sock, enum mnsh_msg_type type,
   if (size < 0)
     mnsh_maybe_mourn_peer ();
 
-  if (debug_linux_namespaces)
-    {
-      debug_printf ("mnsh: send: ");
-      mnsh_debug_print_message (type, fd, int1, int2, buf, bufsiz);
-      debug_printf (" -> %s\n", pulongest (size));
-    }
+  linux_namespaces_debug_printf
+    ("send: %s -> %s",
+     mnsh_debug_print_message (type, fd, int1, int2, buf, bufsiz).c_str (),
+     pulongest (size));
 
   return size;
 }
@@ -445,9 +446,8 @@ mnsh_recv_message (int sock, enum mnsh_msg_type *type,
   size = recvmsg (sock, &msg, MSG_CMSG_CLOEXEC);
   if (size < 0)
     {
-      if (debug_linux_namespaces)
-	debug_printf ("namespace-helper: recv failed (%s)\n",
-		      pulongest (size));
+      linux_namespaces_debug_printf
+	("namespace-helper: recv failed (%s)", pulongest (size));
 
       mnsh_maybe_mourn_peer ();
 
@@ -457,9 +457,9 @@ mnsh_recv_message (int sock, enum mnsh_msg_type *type,
   /* Check for truncation.  */
   if (size < fixed_size || (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC)))
     {
-      if (debug_linux_namespaces)
-	debug_printf ("namespace-helper: recv truncated (%s 0x%x)\n",
-		      pulongest (size), msg.msg_flags);
+      linux_namespaces_debug_printf
+	("namespace-helper: recv truncated (%s 0x%x)",
+	 pulongest (size), msg.msg_flags);
 
       mnsh_maybe_mourn_peer ();
 
@@ -477,13 +477,10 @@ mnsh_recv_message (int sock, enum mnsh_msg_type *type,
   else
     *fd = -1;
 
-  if (debug_linux_namespaces)
-    {
-      debug_printf ("mnsh: recv: ");
-      mnsh_debug_print_message (*type, *fd, *int1, *int2, buf,
-				size - fixed_size);
-      debug_printf ("\n");
-    }
+  linux_namespaces_debug_printf
+    ("recv: %s",
+     mnsh_debug_print_message (*type, *fd, *int1, *int2, buf,
+			       size - fixed_size).c_str ());
 
   /* Return the number of bytes of data in BUF.  */
   return size - fixed_size;
@@ -673,7 +670,7 @@ linux_mntns_get_helper (void)
 	  mnsh_creator_pid = helper_creator;
 
 	  /* Debug printing isn't async-signal-safe.  */
-	  debug_linux_namespaces = 0;
+	  debug_linux_namespaces = false;
 
 	  mnsh_main (sv[1]);
 	}
@@ -685,9 +682,8 @@ linux_mntns_get_helper (void)
       helper->sock = sv[0];
       helper->nsid = ns->id;
 
-      if (debug_linux_namespaces)
-	debug_printf ("Started mount namespace helper process %d\n",
-		      helper->pid);
+      linux_namespaces_debug_printf
+	("Started mount namespace helper process %d", helper->pid);
     }
 
   return helper;

gdb/nat/linux-namespaces.h

@@ -24,6 +24,12 @@
 
 extern bool debug_linux_namespaces;
 
+/* Print a "linux-namespaces" debug statement.  */
+
+#define linux_namespaces_debug_printf(fmt, ...) \
+  debug_prefixed_printf_cond (debug_linux_namespaces, "linux-namespaces", \
+			      fmt, ##__VA_ARGS__)
+
 /* Enumeration of Linux namespace types.  */
 
 enum linux_ns_type