[Libguestfs] [PATCH nbdkit] server: Add -D nbdkit.environ=1 to dump the environment

[Richard W.M. Jones]

This is not secure so should not be used routinely.  Also we do not
attempt to filter environment variables, so even ones containing
multiple lines or special characters are all sent to nbdkit_debug.

The reason for adding this is to allow for debugging the new
nbd_set_socket_activation_name(3) API added in libnbd 1.16.
---
 docs/nbdkit.pod | 10 ++++++++++
 server/main.c   | 28 ++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/docs/nbdkit.pod b/docs/nbdkit.pod
index 83cf6a11c..22350cc08 100644
--- a/docs/nbdkit.pod
+++ b/docs/nbdkit.pod
@@ -619,6 +619,16 @@ are numerous and not usually very interesting.
 S<I<-D nbdkit.backend.controlpath=0>> suppresses the non-datapath
 commands (config, open, close, can_write, etc.)
 
+=item B<-D nbdkit.environ=1>
+
+(not Windows)
+
+Print nbdkit's environment variables in the debug output at start up.
+This is insecure because environment variables may contain both
+sensitive and user-controlled information, so it should not be used
+routinely.  But it is useful for tracking down problems related to
+environment variables.
+
 =item B<-D nbdkit.tls.log=>N
 
 Enable TLS logging.  C<N> can be in the range 0 (no logging) to 99.
diff --git a/server/main.c b/server/main.c
index 1df5d69ac..7b6adc3cc 100644
--- a/server/main.c
+++ b/server/main.c
@@ -210,6 +210,26 @@ dump_config (void)
 #endif
 }
 
+#ifndef WIN32
+
+/* -D nbdkit.environ=1 to dump the environment at start up. */
+NBDKIT_DLL_PUBLIC int nbdkit_debug_environ;
+
+#ifndef HAVE_ENVIRON_DECL
+extern char **environ;
+#endif
+
+static void
+dump_environment (void)
+{
+  size_t i;
+
+  for (i = 0; environ[i]; ++i)
+    nbdkit_debug ("%s", environ[i]);
+}
+
+#endif /* !WIN32 */
+
 int
 main (int argc, char *argv[])
 {
@@ -662,6 +682,14 @@ main (int argc, char *argv[])
   /* Check all debug flags were used, and free them. */
   free_debug_flags ();
 
+#ifndef WIN32
+  /* Dump the environment if asked.  This is the earliest we can do it
+   * because it uses a debug flag.
+   */
+  if (nbdkit_debug_environ && verbose)
+    dump_environment ();
+#endif
+
   if (help) {
     struct backend *b;
 
-- 
2.39.2