Use RemoteCommand option for Tramp's sshx and scpx methods

* doc/misc/tramp.texi (Inline methods) <sshx>:
(External methods) <scpx>: Adapt call sequence.
(Remote shell setup): Mention, that sshx and scpx overwrite
RemoteCommand.
(Remote processes): Restriction: direct asynchronous processes
cannot be used when RemoteCommand is in use.
`tramp-remote-process-environment' is not ignored any longer.

* lisp/net/tramp-sh.el (tramp-methods) <sshx, scpx>: Handle login
shell via RemoteCommand.  Remove `tramp-direct-async' parameter.
(tramp-maybe-open-connection): Add "-i" to login.

* lisp/net/tramp-smb.el (tramp-smb-errors):
Add "NT_STATUS_NOT_SUPPORTED".
(tramp-smb-handle-insert-directory): Fix point moving error.

* test/lisp/net/tramp-tests.el (tramp-test34-explicit-shell-file-name):
Use `get-buffer-process' where appropriate.

doc/misc/tramp.texi

@@ -810,9 +810,10 @@ behavior.
 @cindex @option{sshx} method
 
 Works like @option{ssh} but without the extra authentication prompts.
-@option{sshx} uses @samp{ssh -t -t @var{host} -l @var{user} /bin/sh}
-to open a connection with a ``standard'' login shell.  It supports
-changing the remote login shell @command{/bin/sh}.
+@option{sshx} uses @samp{ssh -t -t -l @var{user} -o
+RemoteCommand='/bin/sh -i' @var{host}} to open a connection with a
+``standard'' login shell.  It supports changing the remote login shell
+@command{/bin/sh}.
 
 @strong{Note} that @option{sshx} does not bypass authentication
 questions.  For example, if the host key of the remote host is not
@@ -935,9 +936,10 @@ This method supports the @samp{-p} argument.
 @cindex @command{ssh} (with @option{scpx} method)
 
 @option{scpx} is useful to avoid login shell questions.  It is similar
-in performance to @option{scp}.  @option{scpx} uses @samp{ssh -t -t
-@var{host} -l @var{user} /bin/sh} to open a connection.  It supports
-changing the remote login shell @command{/bin/sh}.
+in performance to @option{scp}.  @option{scpx} uses @samp{ssh -t -t -l
+@var{user} -o RemoteCommand='/bin/sh -i' @var{host}} to open a
+connection.  It supports changing the remote login shell
+@command{/bin/sh}.
 
 @option{scpx} is useful for MS Windows users when @command{ssh}
 triggers an error about allocating a pseudo tty.  This happens due to
@@ -2220,7 +2222,10 @@ This uses also the settings in @code{tramp-sh-extra-args}.
 @vindex RemoteCommand@r{, ssh option}
 @strong{Note}: If you use an @option{ssh}-based method for connection,
 do @emph{not} set the @option{RemoteCommand} option in your
-@command{ssh} configuration, for example to @command{screen}.
+@command{ssh} configuration, for example to @command{screen}.  On the
+other hand, some @option{ssh}-based methods, like @option{sshx} or
+@option{scpx}, silently overwrite a @option{RemoteCommand} option of
+the configuration file.
 
 
 @subsection Other remote shell setup hints
@@ -3580,13 +3585,16 @@ Furthermore, this approach has the following limitations:
 It works only for connection methods defined in @file{tramp-sh.el} and
 @file{tramp-adb.el}.
 
-@vindex ControlMaster@r{, ssh option}
 @item
 It does not support interactive user authentication.  With
 @option{ssh}-based methods, this can be avoided by using a password
 agent like @command{ssh-agent}, using public key authentication, or
 using @option{ControlMaster} options.
 
+@item
+It cannot be applied for @option{ssh}-based methods, which use the
+@option{RemoteCommand} option.
+
 @item
 It cannot be killed via @code{interrupt-process}.
 
@@ -3597,8 +3605,7 @@ It does not report the remote terminal name via @code{process-tty-name}.
 It does not set process property @code{remote-pid}.
 
 @item
-It does not use @code{tramp-remote-path} and
-@code{tramp-remote-process-environment}.
+It does not use @code{tramp-remote-path}.
 @end itemize
 
 In order to gain even more performance, it is recommended to bind

lisp/net/tramp-sh.el

@@ -181,10 +181,9 @@ The string is used in `tramp-methods'.")
               `("scpx"
                 (tramp-login-program        "ssh")
                 (tramp-login-args           (("-l" "%u") ("-p" "%p") ("%c")
-				             ("-e" "none") ("-t" "-t") ("%h")
-					     ("%l")))
+				             ("-e" "none") ("-t" "-t")
+					     ("-o" "RemoteCommand='%l'") ("%h")))
                 (tramp-async-args           (("-q")))
-                (tramp-direct-async         t)
                 (tramp-remote-shell         ,tramp-default-remote-shell)
                 (tramp-remote-shell-login   ("-l"))
                 (tramp-remote-shell-args    ("-c"))
@@ -238,10 +237,9 @@ The string is used in `tramp-methods'.")
               `("sshx"
                 (tramp-login-program        "ssh")
                 (tramp-login-args           (("-l" "%u") ("-p" "%p") ("%c")
-				             ("-e" "none") ("-t" "-t") ("%h")
-					     ("%l")))
+				             ("-e" "none") ("-t" "-t")
+					     ("-o" "RemoteCommand='%l'") ("%h")))
                 (tramp-async-args           (("-q")))
-                (tramp-direct-async         t)
                 (tramp-remote-shell         ,tramp-default-remote-shell)
                 (tramp-remote-shell-login   ("-l"))
                 (tramp-remote-shell-args    ("-c"))))
@@ -5124,7 +5122,7 @@ connection if a previous connection has died for some reason."
 		     options (format-spec options spec)
 		     spec (format-spec-make
 			   ?h l-host ?u l-user ?p l-port ?c options
-			   ?l (concat remote-shell " " extra-args))
+			   ?l (concat remote-shell " " extra-args " -i"))
 		     command
 		     (concat
 		      ;; We do not want to see the trailing local

lisp/net/tramp-smb.el

@@ -156,6 +156,7 @@ this variable (\"client min protocol=NT1\") ."
 	 "NT_STATUS_NO_SUCH_FILE"
 	 "NT_STATUS_NO_SUCH_USER"
 	 "NT_STATUS_NOT_A_DIRECTORY"
+	 "NT_STATUS_NOT_SUPPORTED"
 	 "NT_STATUS_OBJECT_NAME_COLLISION"
 	 "NT_STATUS_OBJECT_NAME_INVALID"
 	 "NT_STATUS_OBJECT_NAME_NOT_FOUND"
@@ -371,17 +372,17 @@ pass to the OPERATION."
 	(tramp-error
 	 v2 'file-error
 	 "add-name-to-file: %s must not be a directory" filename))
-	;; Do the 'confirm if exists' thing.
-	(when (file-exists-p newname)
-	  ;; What to do?
-	  (if (or (null ok-if-already-exists) ; not allowed to exist
-		  (and (numberp ok-if-already-exists)
-		       (not (yes-or-no-p
-			     (format
-			      "File %s already exists; make it a link anyway? "
-			      v2-localname)))))
-	      (tramp-error v2 'file-already-exists newname)
-	    (delete-file newname)))
+      ;; Do the 'confirm if exists' thing.
+      (when (file-exists-p newname)
+	;; What to do?
+	(if (or (null ok-if-already-exists) ; not allowed to exist
+		(and (numberp ok-if-already-exists)
+		     (not (yes-or-no-p
+			   (format
+			    "File %s already exists; make it a link anyway? "
+			    v2-localname)))))
+	    (tramp-error v2 'file-already-exists newname)
+	  (delete-file newname)))
       ;; We must also flush the cache of the directory, because
       ;; `file-attributes' reads the values from there.
       (tramp-flush-file-properties v2 v2-localname)
@@ -1166,7 +1167,6 @@ PRESERVE-UID-GID and PRESERVE-EXTENDED-ATTRIBUTES are completely ignored."
 		   (insert " -> " (tramp-compat-file-attribute-type attr))))
 
 	       (insert "\n")
-	       (forward-line)
 	       (beginning-of-line)))
 	   entries))))))
 

test/lisp/net/tramp-tests.el

@@ -5247,7 +5247,7 @@ Use direct async.")
 	  ;; order to avoid a question.  `explicit-sh-args' echoes the
 	  ;; test data.
 	  (with-current-buffer (get-buffer-create "*shell*")
-	    (ignore-errors (kill-process (current-buffer)))
+	    (ignore-errors (kill-process (get-buffer-process (current-buffer))))
 	    (should-not explicit-shell-file-name)
 	    (call-interactively #'shell)
 	    (with-timeout (10)