pty_prealloc.c

/*-
 * Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
 * All rights reserved.
 * Copyright 2015-2024 Rivoreo
 *
 * Portions of this software were developed under sponsorship from Snow
 * B.V., the Netherlands.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <sys/conf.h>
#include <sys/malloc.h>
#include <sys/fcntl.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/tty.h>
#include <fs/devfs/devfs_int.h>

/*
 * This driver implements a BSD-style compatibility naming scheme for
 * the pts(4) driver. We just call into pts(4) to create the actual PTY.
 * To make sure we don't use the same PTY multiple times, we abuse
 * si_drv1 inside the cdev to mark whether the PTY is in use.
 *
 * This version preallocates pty master devices in devfs.
 */

struct pts_softc {
	int		pts_unit;	/* (c) Device unit number. */
	unsigned int	pts_flags;	/* (t) Device flags. */
	char		pts_pkt;	/* (t) Unread packet mode data. */
	struct cv	pts_inwait;	/* (t) Blocking write() on master. */
	struct selinfo	pts_inpoll;	/* (t) Select queue for write(). */
	struct cv	pts_outwait;	/* (t) Blocking read() on master. */
	struct selinfo	pts_outpoll;	/* (t) Select queue for read(). */
	struct cdev	*pts_cdev;	/* (c) Master device node. */
	struct ucred	*pts_cred;	/* (c) Resource limit. */
};

static unsigned int pty_warningcnt = 1;
SYSCTL_UINT(_kern, OID_AUTO, pty_warningcnt, CTLFLAG_RW,
    &pty_warningcnt, 0,
    "Warnings that will be triggered upon legacy PTY allocation");

static unsigned int pty_preallocate_count = 256;

static void remove_master_dev_pointer_from_pts(const char *slave_name) {
	struct cdev_priv *cdp;
	TAILQ_FOREACH(cdp, &cdevp_list, cdp_list) {
		if(strcmp(cdp->cdp_c.si_name, slave_name) == 0) {
			struct tty *tty = cdp->cdp_c.si_drv1;
			if(!tty) break;
			struct pts_softc *ptsc = tty->t_devswsoftc;
			if(!ptsc) break;
			ptsc->pts_cdev = NULL;
			break;
		}
	}
}

static int
ptydev_fdopen(struct cdev *dev, int fflags, struct thread *td, struct file *fp)
{
	int error;
	char name[6]; /* "ttyXX" */

	if (!atomic_cmpset_ptr((uintptr_t *)&dev->si_drv1, 0, 1))
		return (EBUSY);

	/* Generate device name and create PTY. */
	strlcpy(name, devtoname(dev), sizeof(name));
	name[0] = 't';

	error = pts_alloc_external(fflags & (FREAD|FWRITE), td, fp, dev, name);
	if(error) return error;

	remove_master_dev_pointer_from_pts(name);

	/* Raise a warning when a legacy PTY has been allocated. */
	counted_warning(&pty_warningcnt, "is using legacy pty devices");

	return (0);
}

static int ptydev_close(struct cdev *dev, int __unused f_flags, int __unused dev_type, struct thread *__unused td) {
	char slave_name[6];
	slave_name[0] = 't';
	strlcpy(slave_name + 1, devtoname(dev) + 1, sizeof slave_name - 1);
	remove_master_dev_pointer_from_pts(slave_name);
	dev->si_drv1 = 0;
	return 0;
}

static struct cdevsw ptydev_cdevsw = {
	.d_version	= D_VERSION,
	.d_fdopen	= ptydev_fdopen,
	.d_close	= ptydev_close,
	.d_name		= "ptydev",
};

MALLOC_DEFINE(M_PTYDEV, "ptydev_array", "Pool for holding pointers to pty cdevs");

static unsigned int preallocated_pty_count = 0;
static struct cdev **preallocated_pty;

#define PTY_NAME_1 "pqrslmnoPQRSLMNO"
#define PTY_NAME_2 "0123456789abcdefghijklmnopqrstuv"

static int reallocate_pty() {
	int e = 0;
	//printf("reallocate_pty: pty_preallocate_count = %u, preallocated_pty_count = %u\n", pty_preallocate_count, preallocated_pty_count);
	if(pty_preallocate_count < preallocated_pty_count) {
		do {
			struct cdev *dev = preallocated_pty[--preallocated_pty_count];
			if(!atomic_cmpset_ptr((uintptr_t *)&dev->si_drv1, 0, 1)) {
				preallocated_pty_count++;
				e = EBUSY;
				break;
			}
			destroy_dev(dev);
		} while(pty_preallocate_count < preallocated_pty_count);
		preallocated_pty = realloc(preallocated_pty, preallocated_pty_count * sizeof(struct cdev *), M_PTYDEV, M_WAITOK);
	} else if(pty_preallocate_count > preallocated_pty_count) {
		const char *u1 = PTY_NAME_1;
		const char *u2 = PTY_NAME_2;
		unsigned int count = 0;
		preallocated_pty = realloc(preallocated_pty, pty_preallocate_count * sizeof(struct cdev *), M_PTYDEV, M_WAITOK);
		for(u1 = PTY_NAME_1; *u1; u1++) {
			for(u2 = PTY_NAME_2; *u2; u2++) {
				struct cdev *dev;
				if(count < preallocated_pty_count) {
					count++;
					continue;
				}
				e = make_dev_p(MAKEDEV_ETERNAL_KLD, &dev, &ptydev_cdevsw, NULL, UID_ROOT, GID_WHEEL, 0666, "pty%c%c", *u1, *u2);
				if(e) goto done; 
				preallocated_pty[count++] = dev;
				if(count >= pty_preallocate_count) goto done;
			}
		}
done:
		preallocated_pty_count = count;
	}
	pty_preallocate_count = preallocated_pty_count;
	return e;
}

static int pty_preallocate_sysctl_handler(SYSCTL_HANDLER_ARGS) {
	unsigned int value = pty_preallocate_count;
	int e = sysctl_handle_int(oidp, &value, 0, req);
	if(e) return e;
	if(!req->newptr) return 0;
	if(value > (sizeof PTY_NAME_1 - 1) * (sizeof PTY_NAME_2 - 1)) {
		//printf("pty_prealloc: requested preallocation number too large\n");
		return EINVAL;
	}
	pty_preallocate_count = value;
	if(!M_PTYDEV->ks_handle) return 0;	// Due to CTLFLAG_TUN
	e = reallocate_pty();
	if(e) printf("pty_prealloc: kern.pty_preallocate: reallocate_pty error %d\n", e);
	return 0;
}

SYSCTL_OID(_kern, OID_AUTO, pty_preallocate, CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_TUN, SYSCTL_NULL_INT_PTR, 0, pty_preallocate_sysctl_handler, "I", "Number of pty master devices to preallocate");

static int
pty_prealloc_modevent(module_t __unused mod, int type, void *__unused data)
{
	int e;
	switch(type) {
	case MOD_LOAD:
		if(module_lookupbyname("pty")) {
			printf("pty_prealloc: conflicting module pty already loaded\n");
			return EBUSY;
		}
		e = reallocate_pty();
		if(e) return e;
		break;
	case MOD_SHUTDOWN:
		break;
	case MOD_UNLOAD:
		// TODO: need locking
		pty_preallocate_count = 0;
		e = reallocate_pty();
		if(e) return e;
		free(preallocated_pty, M_PTYDEV);
		break;
	default:
		return (EOPNOTSUPP);
	}

	return (0);
}

DEV_MODULE(pty_prealloc, pty_prealloc_modevent, NULL);