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binutils-gdb/gdb/serial.h
Pedro Alves 00340e1b91 Introduce a serial interface for select'able events 
This patch adds a new "event" struct serial type, that is an
abstraction specifically for waking up blocking waits/selects,
implemented on top of a pipe on POSIX, and on top of a native Windows
event (CreateEvent, etc.) on Windows.

This will be used to plug signal handler / mainline code races.

For example, GDB can indefinitely delay handling a quit request if the
user presses Ctrl-C between the last QUIT call and the next (blocking)
gdb_select call in the event loop:

      QUIT;
                  <<< press ctrl-c here and end up blocked in gdb_select
		      indefinitely.

      gdb_select (...); // whoops, SIGINT was already handled, no EINTR.

A global alone (either the quit flag, or the "ready" flag of the async
signal handlers in the event loop) is not sufficient.

To plug races such as these on POSIX systems, we have to register some
waitable file descriptor in the set of files gdb_select waits on, and
write to it from the signal handler.  This is classically a pipe, and
the pattern called the self-pipe trick.  On Linux, it could be a more
efficient eventfd instead, but I'm sticking with a pipe for
simplifity, as we need it for portability anyway.

(Alternatively, we could use pselect/ppoll, and block signals until
the pselect.  The latter is not a design I think GDB could use,
because we want the QUIT macro to be super cheap, as it is used in
loops.  Plus, Windows.)

This is a "struct serial" because Windows's gdb_select relies on that.
Windows's gdb_select, our "select" replacement, knows how to wait on
all kinds of handles (regular files, pipes, sockets, console, etc.)
unlike the native Windows "select" function, which can only wait on
sockets.  Each file descriptor for a "serial" type that is not
normally waitable with WaitForMultipleObjects must have a
corresponding struct serial instance.  gdb_select then internally
looks up the struct serial instance that wraps each file descriptor,
and asks it for the corresponding Windows waitable handle.

We could use serial_pipe() to create a "struct serial"-wrapped pipe
that is usable everywhere, including Windows.  That's what currently
python/python.c uses for cross-thread posting of events.

However, serial_write and serial_readchar are not designed to be
async-signal-safe on POSIX hosts.  It's easier to bypass those when
setting/clearing the event source.

And writing and a serial pipe is a bit heavy weight on Windows.
gdb_select requires an extra thread to wait on the pipe and several
Windows events, when a single manual-reset Windows event, with no
extra thread is sufficient.

The intended usage is simply:

- Call make_serial_event to create a serial event object.

- From the signal handler call serial_event_set to set the event.

- From mainline code, have select/poll wait for serial_event_fd(), in
  addition to whatever other files you're about to wait for.

gdb/ChangeLog:
2016-04-12  Pedro Alves  <palves@redhat.com>

	* Makefile.in (SFILES): Add ser-event.c.
	(HFILES_NO_SRCDIR): Add ser-event.h.
	(COMMON_OBS): Add ser-event.o.
	* ser-event.c, ser-event.h: New files.
	* serial.c (new_serial): New function, factored out from
	(serial_fdopen_ops): ... this.
	(serial_open_ops_1): New function, factored out from
	(serial_open): ... this.
	(serial_open_ops): New function.
	* serial.h (struct serial): Forware declare.
	(serial_open_ops): New declaration.
2016-04-12 16:53:21 +01:00

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/* Remote serial support interface definitions for GDB, the GNU Debugger.
Copyright (C) 1992-2016 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef SERIAL_H
#define SERIAL_H
#ifdef USE_WIN32API
#include <winsock2.h>
#include <windows.h>
#endif
struct ui_file;
/* For most routines, if a failure is indicated, then errno should be
examined. */
/* Terminal state pointer. This is specific to each type of
interface. */
typedef void *serial_ttystate;
struct serial;
struct serial_ops;
/* Create a new serial for OPS. The new serial is not opened. */
/* Try to open NAME. Returns a new `struct serial *' on success, NULL
on failure. The new serial object has a reference count of 1.
Note that some open calls can block and, if possible, should be
written to be non-blocking, with calls to ui_look_hook so they can
be cancelled. An async interface for open could be added to GDB if
necessary. */
extern struct serial *serial_open (const char *name);
/* Open a new serial stream using OPS. */
extern struct serial *serial_open_ops (const struct serial_ops *ops);
/* Returns true if SCB is open. */
extern int serial_is_open (struct serial *scb);
/* Find an already opened serial stream using a file handle. */
extern struct serial *serial_for_fd (int fd);
/* Open a new serial stream using a file handle. */
extern struct serial *serial_fdopen (const int fd);
/* Push out all buffers, close the device and unref SCB. */
extern void serial_close (struct serial *scb);
/* Increment reference count of SCB. */
extern void serial_ref (struct serial *scb);
/* Decrement reference count of SCB. */
extern void serial_unref (struct serial *scb);
/* Create a pipe, and put the read end in files[0], and the write end
in filde[1]. Returns 0 for success, negative value for error (in
which case errno contains the error). */
extern int gdb_pipe (int fildes[2]);
/* Create a pipe with each end wrapped in a `struct serial' interface.
Put the read end in scbs[0], and the write end in scbs[1]. Returns
0 for success, negative value for error (in which case errno
contains the error). */
extern int serial_pipe (struct serial *scbs[2]);
/* Push out all buffers and destroy SCB without closing the device. */
extern void serial_un_fdopen (struct serial *scb);
/* Read one char from the serial device with TIMEOUT seconds to wait
or -1 to wait forever. Use timeout of 0 to effect a poll.
Infinite waits are not permitted. Returns unsigned char if ok, else
one of the following codes. Note that all error return-codes are
guaranteed to be < 0. */
enum serial_rc {
SERIAL_ERROR = -1, /* General error. */
SERIAL_TIMEOUT = -2, /* Timeout or data-not-ready during read.
Unfortunately, through
deprecated_ui_loop_hook (), this can also
be a QUIT indication. */
SERIAL_EOF = -3 /* General end-of-file or remote target
connection closed, indication. Includes
things like the line dropping dead. */
};
extern int serial_readchar (struct serial *scb, int timeout);
/* Write COUNT bytes from BUF to the port SCB. Returns 0 for
success, non-zero for failure. */
extern int serial_write (struct serial *scb, const void *buf, size_t count);
/* Write a printf style string onto the serial port. */
extern void serial_printf (struct serial *desc,
const char *,...) ATTRIBUTE_PRINTF (2, 3);
/* Allow pending output to drain. */
extern int serial_drain_output (struct serial *);
/* Flush (discard) pending output. Might also flush input (if this
system can't flush only output). */
extern int serial_flush_output (struct serial *);
/* Flush pending input. Might also flush output (if this system can't
flush only input). */
extern int serial_flush_input (struct serial *);
/* Send a break between 0.25 and 0.5 seconds long. */
extern int serial_send_break (struct serial *scb);
/* Turn the port into raw mode. */
extern void serial_raw (struct serial *scb);
/* Return a pointer to a newly malloc'd ttystate containing the state
of the tty. */
extern serial_ttystate serial_get_tty_state (struct serial *scb);
/* Return a pointer to a newly malloc'd ttystate containing a copy
of the state in TTYSTATE. */
extern serial_ttystate serial_copy_tty_state (struct serial *scb,
serial_ttystate ttystate);
/* Set the state of the tty to TTYSTATE. The change is immediate.
When changing to or from raw mode, input might be discarded.
Returns 0 for success, negative value for error (in which case
errno contains the error). */
extern int serial_set_tty_state (struct serial *scb, serial_ttystate ttystate);
/* printf_filtered a user-comprehensible description of ttystate on
the specified STREAM. FIXME: At present this sends output to the
default stream - GDB_STDOUT. */
extern void serial_print_tty_state (struct serial *scb,
serial_ttystate ttystate,
struct ui_file *);
/* Set the tty state to NEW_TTYSTATE, where OLD_TTYSTATE is the
current state (generally obtained from a recent call to
serial_get_tty_state()), but be careful not to discard any input.
This means that we never switch in or out of raw mode, even if
NEW_TTYSTATE specifies a switch. */
extern int serial_noflush_set_tty_state (struct serial *scb,
serial_ttystate new_ttystate,
serial_ttystate old_ttystate);
/* Set the baudrate to the decimal value supplied. Returns 0 for
success, -1 for failure. */
extern int serial_setbaudrate (struct serial *scb, int rate);
/* Set the number of stop bits to the value specified. Returns 0 for
success, -1 for failure. */
#define SERIAL_1_STOPBITS 1
#define SERIAL_1_AND_A_HALF_STOPBITS 2 /* 1.5 bits, snicker... */
#define SERIAL_2_STOPBITS 3
extern int serial_setstopbits (struct serial *scb, int num);
#define GDBPARITY_NONE 0
#define GDBPARITY_ODD 1
#define GDBPARITY_EVEN 2
/* Set parity for serial port. Returns 0 for success, -1 for failure. */
extern int serial_setparity (struct serial *scb, int parity);
/* Asynchronous serial interface: */
/* Can the serial device support asynchronous mode? */
extern int serial_can_async_p (struct serial *scb);
/* Has the serial device been put in asynchronous mode? */
extern int serial_is_async_p (struct serial *scb);
/* For ASYNC enabled devices, register a callback and enable
asynchronous mode. To disable asynchronous mode, register a NULL
callback. */
typedef void (serial_event_ftype) (struct serial *scb, void *context);
extern void serial_async (struct serial *scb,
serial_event_ftype *handler, void *context);
/* Trace/debug mechanism.
serial_debug() enables/disables internal debugging.
serial_debug_p() indicates the current debug state. */
extern void serial_debug (struct serial *scb, int debug_p);
extern int serial_debug_p (struct serial *scb);
/* Details of an instance of a serial object. */
struct serial
{
/* serial objects are ref counted (but not the underlying
connection, just the object's lifetime in memory). */
int refcnt;
int fd; /* File descriptor */
/* File descriptor for a separate error stream that should be
immediately forwarded to gdb_stderr. This may be -1.
If != -1, this descriptor should be non-blocking or
ops->avail should be non-NULL. */
int error_fd;
const struct serial_ops *ops; /* Function vector */
void *state; /* Local context info for open FD */
serial_ttystate ttystate; /* Not used (yet) */
int bufcnt; /* Amount of data remaining in receive
buffer. -ve for sticky errors. */
unsigned char *bufp; /* Current byte */
unsigned char buf[BUFSIZ]; /* Da buffer itself */
int current_timeout; /* (ser-unix.c termio{,s} only), last
value of VTIME */
int timeout_remaining; /* (ser-unix.c termio{,s} only), we
still need to wait for this many
more seconds. */
struct serial *next; /* Pointer to the next `struct serial *' */
int debug_p; /* Trace this serial devices operation. */
int async_state; /* Async internal state. */
void *async_context; /* Async event thread's context */
serial_event_ftype *async_handler;/* Async event handler */
};
struct serial_ops
{
char *name;
int (*open) (struct serial *, const char *name);
void (*close) (struct serial *);
int (*fdopen) (struct serial *, int fd);
int (*readchar) (struct serial *, int timeout);
int (*write) (struct serial *, const void *buf, size_t count);
/* Discard pending output */
int (*flush_output) (struct serial *);
/* Discard pending input */
int (*flush_input) (struct serial *);
int (*send_break) (struct serial *);
void (*go_raw) (struct serial *);
serial_ttystate (*get_tty_state) (struct serial *);
serial_ttystate (*copy_tty_state) (struct serial *, serial_ttystate);
int (*set_tty_state) (struct serial *, serial_ttystate);
void (*print_tty_state) (struct serial *, serial_ttystate,
struct ui_file *);
int (*noflush_set_tty_state) (struct serial *, serial_ttystate,
serial_ttystate);
int (*setbaudrate) (struct serial *, int rate);
int (*setstopbits) (struct serial *, int num);
/* Set the value PARITY as parity setting for serial object.
Return 0 in the case of success. */
int (*setparity) (struct serial *, int parity);
/* Wait for output to drain. */
int (*drain_output) (struct serial *);
/* Change the serial device into/out of asynchronous mode, call
the specified function when ever there is something
interesting. */
void (*async) (struct serial *scb, int async_p);
/* Perform a low-level read operation, reading (at most) COUNT
bytes into SCB->BUF. Return zero at end of file. */
int (*read_prim)(struct serial *scb, size_t count);
/* Perform a low-level write operation, writing (at most) COUNT
bytes from BUF. */
int (*write_prim)(struct serial *scb, const void *buf, size_t count);
/* Return that number of bytes that can be read from FD
without blocking. Return value of -1 means that the
read will not block even if less that requested bytes
are available. */
int (*avail)(struct serial *scb, int fd);
#ifdef USE_WIN32API
/* Return a handle to wait on, indicating available data from SCB
when signaled, in *READ. Return a handle indicating errors
in *EXCEPT. */
void (*wait_handle) (struct serial *scb, HANDLE *read, HANDLE *except);
void (*done_wait_handle) (struct serial *scb);
#endif /* USE_WIN32API */
};
/* Add a new serial interface to the interface list. */
extern void serial_add_interface (const struct serial_ops * optable);
/* File in which to record the remote debugging session. */
extern void serial_log_command (struct target_ops *self, const char *);
#ifdef USE_WIN32API
/* Windows-only: find or create handles that we can wait on for this
serial device. */
extern void serial_wait_handle (struct serial *, HANDLE *, HANDLE *);
/* Windows-only: signal that we are done with the wait handles. */
extern void serial_done_wait_handle (struct serial *);
#endif /* USE_WIN32API */
#endif /* SERIAL_H */
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