gdb/

gdb/
	* target.h (struct target_ops): Delete to_async_mask_value and add
	to_async_mask.
	(target_is_async_p, target_async): Formatting.
	(target_async_mask_value): Delete.
	(target_async_mask): Delete function declaration, and add new
	target macro with the same name.

	* target.c (update_current_target): Replace to_async_mask_value by
	to_async_mask.  Default to_async_mask to return_one.
	(target_async_mask): Delete.
	(find_default_can_async_p, find_default_is_async_p): New.
	(init_dummy_target): register find_default_can_async_p and
	find_default_is_async_p on the dummy target.

	* linux-nat.c: Include inf-loop.h, event-loop.h and event-top.h.
	(debug_linux_nat_async): New global.
	(show_debug_linux_nat_async): New function.
	(linux_nat_async_enabled, linux_nat_async_mask_value)
	(linux_nat_event_pipe, linux_nat_num_queued_events)
	(linux_nat_async_events_enabled): New globals.
	(struct waitpid_result): New struct.
	(waitpid_queue): New global.
	(queued_waitpid, push_waitpid, drain_queued_events): New.
	(my_waitpid): Call queued_waitpid.
	(linux_child_follow_fork): Disable async events during the call.
	(blocked_mask): Delete.
	(sync_sigchld_action, async_sigchld_action): New globals.
	(lin_lwp_attach_lwp): In sync mode, don't reblock SIGCHLD.  In
	async mode, block events during the call.
	(linux_nat_create_inferior): New.
	(linux_nat_attach): In sync mode, restore the mask states.  In
	async mode, wake the event loop immediatelly.
	(detach_callback): Drain all queued events of the lwp we're
	detaching from.
	(linux_nat_detach): Block async mode, and drain events of the main
	process.
	(linux_nat_resume): If in async mode, mask async events during the
	call.  If short circuiting, force event loop to wake up.  If
	resuming, set target_executing, and register target events in the
	event loop.
	(pipe_to_local_event_queue, local_event_queue_to_pipe): New.
	(linux_nat_wait): In async mode, block events during the call.
	Only enable/disable passing SIGINT to the inferior in sync mode.
	Get events from local waitpid queue.  If no interesting events was
	found, return to events loop.  Reregister target events in the
	event loop on exit.  In sync mode, no need to reblock SIGCHLD.
	(linux_nat_kill): Disable events on entry.
	(linux_nat_mourn_inferior): In sync mode, don't restore the masks
	here.  Detach async mode from the event loop if there are no more
	forks available, otherwise leave it on.
	(sigchld_handler): Assure this is called only in sync mode.
	(linux_async_permitted, linux_async_permitted_1): New globals.
	(set_maintenance_linux_async_permitted)
	(show_maintenance_linux_async_permitted): New functions.
	(linux_nat_is_async_p, linux_nat_can_async_p)
	(linux_nat_async_mask): New.
	(linux_nat_event_pipe_pop, linux_nat_event_pipe_push): New.
	(get_pending_events, async_sigchld_handler): New.
	(linux_nat_async_events): New.
	(async_terminal_is_ours): New global.
	(linux_nat_terminal_inferior, linux_nat_terminal_ours): New.
	(async_client_callback, async_client_context): New.
	(linux_nat_async_file_handler, linux_nat_async)
	(linux_nat_disable_async, linux_nat_enable_async): New.
	(linux_nat_add_target): Register linux_nat_create_inferior,
	linux_nat_can_async_p, linux_nat_is_async_p, linux_nat_async,
	linux_nat_async_mask, linux_nat_terminal_inferior and
	linux_nat_terminal_ours.
	(_initialize_linux_nat): Remove local action variable, and update
	code that used it to use sync_sigchld_action.  Add new
	"lin-lwp-async" debug set/show command.  Put the "lin-lwp" debug
	set/show command in the maintenance class.  Add new "linux-async"
	maintenance set/show command.  Block SIGCHLD by default.  Setup
	async_sichld_action, and sync_sigchld_action.  Install the default
	async mode.
	(lin_thread_get_thread_signals): Use a local sigset_t for blocking
	the cancel signals.

	* linux-thread-db.c (re_check_for_thread_db): New.
	(clear_lwpid_callback): Handle TARGET_WAITKIND_IGNORE.
	(thread_db_can_async_p, thread_db_is_async_p, thread_db_async)
	(thread_db_async_mask): New.
	(init_thread_db_ops): Register thread_db_can_async_p,
	thread_db_is_async_p, thread_db_async and thread_db_async_mask.

	* remote.c (remote_async_mask_value): New.
	(remote_return_zero): New.
	(init_remote_ops): Register remote_return_zero as callbacks of
	to_can_async_p and to_is_async_p.
	(remote_can_async_p, remote_is_async_p, remote_async): Update to
	use remote_async_mask_value.
	(remote_async_mask): New.
	(init_remote_async_ops): Remove to_async_mask_value setting and
	register remote_async_mask as to_async_mask callback in
	remote_async_ops.

	* Makefile.in (linux-nat.o): Update.

gdb/doc/
	* gdb.texinfo (Debugging Output): Document
	"set/show debug lin-lwp-async".
	(Maintenance Commands): Document "maint set/show linux-async".