PR remote/21188: Fix remote serial timeout

As Gareth McMullin <gareth@blacksphere.co.nz> reports at
<https://sourceware.org/ml/gdb-patches/2017-02/msg00560.html>, the
timeout mechanism in ser-unix.c was broken by commit 048094acc
("target remote: Don't rely on immediate_quit (introduce quit
handlers)").

Instead of applying a local fix, and since we now finally always use
interrupt_select [1], let's get rid of hardwire_readchar entirely, and
use ser_base_readchar instead, which has similar timeout handling,
except for the bug.

Smoke tested with:

 $ socat -d -d pty,raw,echo=0 pty,raw,echo=0
 2017/03/14 14:08:13 socat[4994] N PTY is /dev/pts/14
 2017/03/14 14:08:13 socat[4994] N PTY is /dev/pts/15
 2017/03/14 14:08:13 socat[4994] N starting data transfer loop with FDs [3,3] and [5,5]
 $ gdbserver /dev/pts/14 PROG
 $ gdb PROG -ex "tar rem /dev/pts/15"

and then a few continues/ctrl-c's, plus killing gdbserver and socat.

[1] - See FIXME comments being removed.

gdb/ChangeLog:
2017-03-17  Pedro Alves  <palves@redhat.com>

	PR remote/21188
	* ser-base.c (ser_base_wait_for): Add comment.
	(do_ser_base_readchar): Improve comment based on the ser-unix.c's
	version.
	* ser-unix.c (hardwire_raw): Remove reference to
	scb->current_timeout.
	(wait_for, do_hardwire_readchar, hardwire_readchar): Delete.
	(hardwire_ops): Install ser_base_readchar instead of
	hardwire_readchar.
	* serial.h (struct serial) <current_timeout, timeout_remaining>:
	Remove fields.

1 files changed, 10 insertions, 4 deletions

diff --git a/gdb/ser-base.c b/gdb/ser-base.c
index 3e10033..790cb1b 100644
--- a/gdb/ser-base.c
+++ b/gdb/ser-base.c
@@ -205,6 +205,11 @@ push_event (void *context)
 /* Wait for input on scb, with timeout seconds.  Returns 0 on success,
    otherwise SERIAL_TIMEOUT or SERIAL_ERROR.  */
 
+/* NOTE: Some of the code below is dead.  The only possible values of
+   the TIMEOUT parameter are ONE and ZERO.  OTOH, we should probably
+   get rid of the deprecated_ui_loop_hook call in do_ser_base_readchar
+   instead and support infinite time outs here.  */
+
 static int
 ser_base_wait_for (struct serial *scb, int timeout)
 {
@@ -308,10 +313,11 @@ ser_base_read_error_fd (struct serial *scb, int close_fd)
     }
 }
 
-/* Read a character with user-specified timeout.  TIMEOUT is number of seconds
-   to wait, or -1 to wait forever.  Use timeout of 0 to effect a poll.  Returns
-   char if successful.  Returns -2 if timeout expired, EOF if line dropped
-   dead, or -3 for any other error (see errno in that case).  */
+/* Read a character with user-specified timeout.  TIMEOUT is number of
+   seconds to wait, or -1 to wait forever.  Use timeout of 0 to effect
+   a poll.  Returns char if successful.  Returns SERIAL_TIMEOUT if
+   timeout expired, SERIAL_EOF if line dropped dead, or SERIAL_ERROR
+   for any other error (see errno in that case).  */
 
 static int
 do_ser_base_readchar (struct serial *scb, int timeout)