gpg: Add pinentry-mode feature.

* g10/gpg.c: Include shareddefs.h.
(main): Add option --pinentry-mode.
* g10/options.h (struct opt): Add field pinentry_mode.
* g10/passphrase.c: Include shareddefs.h.
(have_static_passphrase): Take care of loopback pinentry_mode.
(read_passphrase_from_fd): Ditto.
(get_static_passphrase): New.
(passphrase_to_dek_ext): Factor some code out to ...
(emit_status_need_passphrase): new.
* g10/call-agent.c (start_agent): Send the pinentry mode.
(default_inq_cb): Take care of the PASSPHRASE inquiry.  Return a
proper error code.
(agent_pksign): Add args keyid, mainkeyid and pubkey_algo.
(agent_pkdecrypt): Ditto.
* g10/pubkey-enc.c (get_it): Pass new args.
* g10/sign.c (do_sign): Pass new args.

* g10/call-agent.c (struct default_inq_parm_s): New.  Change all
similar structs to reference this one.  Change all users and inquire
callback to use this struct, instead of NULL or some undefined but not
used structs.  This change will help to eventually get rid of global
variables.
--

This new features allows to use gpg without a Pinentry.  As a
prerequisite the agent must be configured to allow the loopback
pinentry mode (option --allow-loopback-pinentry).  For example

  gpg2 --pinentry-mode=loopback FILE.gpg

may be used to decrypt FILE.gpg while entering the passphrase on the
tty.  If batch is used, --passphrase et al. may be used, if
--command-fd is used, the passphrase may be provided by another
process.  Note that there are no try-again prompts in case of a bad
passphrase.

g10/passphrase.c

@@ -43,7 +43,7 @@
 #include "i18n.h"
 #include "status.h"
 #include "call-agent.h"
-
+#include "../common/shareddefs.h"
 
 static char *fd_passwd = NULL;
 static char *next_pw = NULL;
@@ -104,9 +104,21 @@ encode_s2k_iterations (int iterations)
 int
 have_static_passphrase()
 {
-  return !!fd_passwd && opt.batch;
+  return (!!fd_passwd
+          && (opt.batch || opt.pinentry_mode == PINENTRY_MODE_LOOPBACK));
 }
 
+/* Return a static passphrase.  The returned value is only valid as
+   long as no other passphrase related function is called.  NULL may
+   be returned if no passphrase has been set; better use
+   have_static_passphrase first.  */
+const char *
+get_static_passphrase (void)
+{
+  return fd_passwd;
+}
+
+
 /****************
  * Set the passphrase to be used for the next query and only for the next
  * one.
@@ -156,7 +168,7 @@ read_passphrase_from_fd( int fd )
   int i, len;
   char *pw;
 
-  if ( !opt.batch )
+  if ( !opt.batch && opt.pinentry_mode != PINENTRY_MODE_LOOPBACK)
     { /* Not used but we have to do a dummy read, so that it won't end
          up at the begin of the message if the quite usual trick to
          prepend the passphtrase to the message is used. */
@@ -187,7 +199,7 @@ read_passphrase_from_fd( int fd )
         break;
     }
   pw[i] = 0;
-  if (!opt.batch)
+  if (!opt.batch && opt.pinentry_mode != PINENTRY_MODE_LOOPBACK)
     tty_printf("\b\b\b   \n" );
 
   xfree ( fd_passwd );
@@ -458,30 +470,9 @@ passphrase_to_dek_ext (u32 *keyid, int pubkey_algo,
 
       if ( keyid )
         {
-          u32 used_kid[2];
-          char *us;
-
-          if ( keyid[2] && keyid[3] )
-            {
-              used_kid[0] = keyid[2];
-              used_kid[1] = keyid[3];
-            }
-          else
-            {
-              used_kid[0] = keyid[0];
-              used_kid[1] = keyid[1];
-            }
-
-          us = get_long_user_id_string ( keyid );
-          write_status_text ( STATUS_USERID_HINT, us );
-          xfree(us);
-
-          snprintf (buf, sizeof buf -1, "%08lX%08lX %08lX%08lX %d 0",
-                    (ulong)keyid[0], (ulong)keyid[1],
-                    (ulong)used_kid[0], (ulong)used_kid[1],
-                    pubkey_algo );
-
-          write_status_text ( STATUS_NEED_PASSPHRASE, buf );
+          emit_status_need_passphrase (keyid,
+                                       keyid[2] && keyid[3]? keyid+2:NULL,
+                                       pubkey_algo);
 	}
       else
         {
@@ -614,6 +605,29 @@ passphrase_to_dek (u32 *keyid, int pubkey_algo,
 }
 
 
+/* Emit the USERID_HINT and the NEED_PASSPHRASE status messages.
+   MAINKEYID may be NULL. */
+void
+emit_status_need_passphrase (u32 *keyid, u32 *mainkeyid, int pubkey_algo)
+{
+  char buf[50];
+  char *us;
+
+  us = get_long_user_id_string (keyid);
+  write_status_text (STATUS_USERID_HINT, us);
+  xfree (us);
+
+  snprintf (buf, sizeof buf -1, "%08lX%08lX %08lX%08lX %d 0",
+            (ulong)keyid[0],
+            (ulong)keyid[1],
+            (ulong)(mainkeyid? mainkeyid[0]:keyid[0]),
+            (ulong)(mainkeyid? mainkeyid[1]:keyid[1]),
+            pubkey_algo);
+
+  write_status_text (STATUS_NEED_PASSPHRASE, buf);
+}
+
+
 /* Return an allocated utf-8 string describing the key PK.  If ESCAPED
    is true spaces and control characters are percent or plus escaped.
    MODE 0 is for the common prompt, MODE 1 for the import prompt. */