linux/drivers/net/ppp_synctty.c
Gabriele Paoloni 9c705260fe ppp: ppp_mp_explode() redesign
I found the PPP subsystem to not work properly when connecting channels
with different speeds to the same bundle.

Problem Description:

As the "ppp_mp_explode" function fragments the sk_buff buffer evenly
among the PPP channels that are connected to a certain PPP unit to
make up a bundle, if we are transmitting using an upper layer protocol
that requires an Ack before sending the next packet (like TCP/IP for
example), we will have a bandwidth bottleneck on the slowest channel
of the bundle.

Let's clarify by an example. Let's consider a scenario where we have
two PPP links making up a bundle: a slow link (10KB/sec) and a fast
link (1000KB/sec) working at the best (full bandwidth). On the top we
have a TCP/IP stack sending a 1000 Bytes sk_buff buffer down to the
PPP subsystem. The "ppp_mp_explode" function will divide the buffer in
two fragments of 500B each (we are neglecting all the headers, crc,
flags etc?.). Before the TCP/IP stack sends out the next buffer, it
will have to wait for the ACK response from the remote peer, so it
will have to wait for both fragments to have been sent over the two
PPP links, received by the remote peer and reconstructed. The
resulting behaviour is that, rather than having a bundle working
@1010KB/sec (the sum of the channels bandwidths), we'll have a bundle
working @20KB/sec (the double of the slowest channels bandwidth).


Problem Solution:

The problem has been solved by redesigning the "ppp_mp_explode"
function in such a way to make it split the sk_buff buffer according
to the speeds of the underlying PPP channels (the speeds of the serial
interfaces respectively attached to the PPP channels). Referring to
the above example, the redesigned "ppp_mp_explode" function will now
divide the 1000 Bytes buffer into two fragments whose sizes are set
according to the speeds of the channels where they are going to be
sent on (e.g .  10 Byets on 10KB/sec channel and 990 Bytes on
1000KB/sec channel).  The reworked function grants the same
performances of the original one in optimal working conditions (i.e. a
bundle made up of PPP links all working at the same speed), while
greatly improving performances on the bundles made up of channels
working at different speeds.

Signed-off-by: Gabriele Paoloni <gabriele.paoloni@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2009-03-13 16:09:12 -07:00

791 lines
18 KiB
C

/*
* PPP synchronous tty channel driver for Linux.
*
* This is a ppp channel driver that can be used with tty device drivers
* that are frame oriented, such as synchronous HDLC devices.
*
* Complete PPP frames without encoding/decoding are exchanged between
* the channel driver and the device driver.
*
* The async map IOCTL codes are implemented to keep the user mode
* applications happy if they call them. Synchronous PPP does not use
* the async maps.
*
* Copyright 1999 Paul Mackerras.
*
* Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
*
* 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
* 2 of the License, or (at your option) any later version.
*
* This driver provides the encapsulation and framing for sending
* and receiving PPP frames over sync serial lines. It relies on
* the generic PPP layer to give it frames to send and to process
* received frames. It implements the PPP line discipline.
*
* Part of the code in this driver was inspired by the old async-only
* PPP driver, written by Michael Callahan and Al Longyear, and
* subsequently hacked by Paul Mackerras.
*
* ==FILEVERSION 20040616==
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/tty.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/ppp_defs.h>
#include <linux/if_ppp.h>
#include <linux/ppp_channel.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
#include <linux/init.h>
#include <asm/uaccess.h>
#define PPP_VERSION "2.4.2"
/* Structure for storing local state. */
struct syncppp {
struct tty_struct *tty;
unsigned int flags;
unsigned int rbits;
int mru;
spinlock_t xmit_lock;
spinlock_t recv_lock;
unsigned long xmit_flags;
u32 xaccm[8];
u32 raccm;
unsigned int bytes_sent;
unsigned int bytes_rcvd;
struct sk_buff *tpkt;
unsigned long last_xmit;
struct sk_buff_head rqueue;
struct tasklet_struct tsk;
atomic_t refcnt;
struct completion dead_cmp;
struct ppp_channel chan; /* interface to generic ppp layer */
};
/* Bit numbers in xmit_flags */
#define XMIT_WAKEUP 0
#define XMIT_FULL 1
/* Bits in rbits */
#define SC_RCV_BITS (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
#define PPPSYNC_MAX_RQLEN 32 /* arbitrary */
/*
* Prototypes.
*/
static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
unsigned long arg);
static void ppp_sync_process(unsigned long arg);
static int ppp_sync_push(struct syncppp *ap);
static void ppp_sync_flush_output(struct syncppp *ap);
static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
char *flags, int count);
static struct ppp_channel_ops sync_ops = {
ppp_sync_send,
ppp_sync_ioctl
};
/*
* Utility procedures to print a buffer in hex/ascii
*/
static void
ppp_print_hex (register __u8 * out, const __u8 * in, int count)
{
register __u8 next_ch;
static const char hex[] = "0123456789ABCDEF";
while (count-- > 0) {
next_ch = *in++;
*out++ = hex[(next_ch >> 4) & 0x0F];
*out++ = hex[next_ch & 0x0F];
++out;
}
}
static void
ppp_print_char (register __u8 * out, const __u8 * in, int count)
{
register __u8 next_ch;
while (count-- > 0) {
next_ch = *in++;
if (next_ch < 0x20 || next_ch > 0x7e)
*out++ = '.';
else {
*out++ = next_ch;
if (next_ch == '%') /* printk/syslogd has a bug !! */
*out++ = '%';
}
}
*out = '\0';
}
static void
ppp_print_buffer (const char *name, const __u8 *buf, int count)
{
__u8 line[44];
if (name != NULL)
printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
while (count > 8) {
memset (line, 32, 44);
ppp_print_hex (line, buf, 8);
ppp_print_char (&line[8 * 3], buf, 8);
printk(KERN_DEBUG "%s\n", line);
count -= 8;
buf += 8;
}
if (count > 0) {
memset (line, 32, 44);
ppp_print_hex (line, buf, count);
ppp_print_char (&line[8 * 3], buf, count);
printk(KERN_DEBUG "%s\n", line);
}
}
/*
* Routines implementing the synchronous PPP line discipline.
*/
/*
* We have a potential race on dereferencing tty->disc_data,
* because the tty layer provides no locking at all - thus one
* cpu could be running ppp_synctty_receive while another
* calls ppp_synctty_close, which zeroes tty->disc_data and
* frees the memory that ppp_synctty_receive is using. The best
* way to fix this is to use a rwlock in the tty struct, but for now
* we use a single global rwlock for all ttys in ppp line discipline.
*
* FIXME: Fixed in tty_io nowdays.
*/
static DEFINE_RWLOCK(disc_data_lock);
static struct syncppp *sp_get(struct tty_struct *tty)
{
struct syncppp *ap;
read_lock(&disc_data_lock);
ap = tty->disc_data;
if (ap != NULL)
atomic_inc(&ap->refcnt);
read_unlock(&disc_data_lock);
return ap;
}
static void sp_put(struct syncppp *ap)
{
if (atomic_dec_and_test(&ap->refcnt))
complete(&ap->dead_cmp);
}
/*
* Called when a tty is put into sync-PPP line discipline.
*/
static int
ppp_sync_open(struct tty_struct *tty)
{
struct syncppp *ap;
int err;
int speed;
if (tty->ops->write == NULL)
return -EOPNOTSUPP;
ap = kzalloc(sizeof(*ap), GFP_KERNEL);
err = -ENOMEM;
if (!ap)
goto out;
/* initialize the syncppp structure */
ap->tty = tty;
ap->mru = PPP_MRU;
spin_lock_init(&ap->xmit_lock);
spin_lock_init(&ap->recv_lock);
ap->xaccm[0] = ~0U;
ap->xaccm[3] = 0x60000000U;
ap->raccm = ~0U;
skb_queue_head_init(&ap->rqueue);
tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
atomic_set(&ap->refcnt, 1);
init_completion(&ap->dead_cmp);
ap->chan.private = ap;
ap->chan.ops = &sync_ops;
ap->chan.mtu = PPP_MRU;
ap->chan.hdrlen = 2; /* for A/C bytes */
speed = tty_get_baud_rate(tty);
ap->chan.speed = speed;
err = ppp_register_channel(&ap->chan);
if (err)
goto out_free;
tty->disc_data = ap;
tty->receive_room = 65536;
return 0;
out_free:
kfree(ap);
out:
return err;
}
/*
* Called when the tty is put into another line discipline
* or it hangs up. We have to wait for any cpu currently
* executing in any of the other ppp_synctty_* routines to
* finish before we can call ppp_unregister_channel and free
* the syncppp struct. This routine must be called from
* process context, not interrupt or softirq context.
*/
static void
ppp_sync_close(struct tty_struct *tty)
{
struct syncppp *ap;
write_lock_irq(&disc_data_lock);
ap = tty->disc_data;
tty->disc_data = NULL;
write_unlock_irq(&disc_data_lock);
if (!ap)
return;
/*
* We have now ensured that nobody can start using ap from now
* on, but we have to wait for all existing users to finish.
* Note that ppp_unregister_channel ensures that no calls to
* our channel ops (i.e. ppp_sync_send/ioctl) are in progress
* by the time it returns.
*/
if (!atomic_dec_and_test(&ap->refcnt))
wait_for_completion(&ap->dead_cmp);
tasklet_kill(&ap->tsk);
ppp_unregister_channel(&ap->chan);
skb_queue_purge(&ap->rqueue);
kfree_skb(ap->tpkt);
kfree(ap);
}
/*
* Called on tty hangup in process context.
*
* Wait for I/O to driver to complete and unregister PPP channel.
* This is already done by the close routine, so just call that.
*/
static int ppp_sync_hangup(struct tty_struct *tty)
{
ppp_sync_close(tty);
return 0;
}
/*
* Read does nothing - no data is ever available this way.
* Pppd reads and writes packets via /dev/ppp instead.
*/
static ssize_t
ppp_sync_read(struct tty_struct *tty, struct file *file,
unsigned char __user *buf, size_t count)
{
return -EAGAIN;
}
/*
* Write on the tty does nothing, the packets all come in
* from the ppp generic stuff.
*/
static ssize_t
ppp_sync_write(struct tty_struct *tty, struct file *file,
const unsigned char *buf, size_t count)
{
return -EAGAIN;
}
static int
ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg)
{
struct syncppp *ap = sp_get(tty);
int __user *p = (int __user *)arg;
int err, val;
if (!ap)
return -ENXIO;
err = -EFAULT;
switch (cmd) {
case PPPIOCGCHAN:
err = -EFAULT;
if (put_user(ppp_channel_index(&ap->chan), p))
break;
err = 0;
break;
case PPPIOCGUNIT:
err = -EFAULT;
if (put_user(ppp_unit_number(&ap->chan), p))
break;
err = 0;
break;
case TCFLSH:
/* flush our buffers and the serial port's buffer */
if (arg == TCIOFLUSH || arg == TCOFLUSH)
ppp_sync_flush_output(ap);
err = tty_perform_flush(tty, arg);
break;
case FIONREAD:
val = 0;
if (put_user(val, p))
break;
err = 0;
break;
default:
err = tty_mode_ioctl(tty, file, cmd, arg);
break;
}
sp_put(ap);
return err;
}
/* No kernel lock - fine */
static unsigned int
ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
{
return 0;
}
/*
* This can now be called from hard interrupt level as well
* as soft interrupt level or mainline.
*/
static void
ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
char *cflags, int count)
{
struct syncppp *ap = sp_get(tty);
unsigned long flags;
if (!ap)
return;
spin_lock_irqsave(&ap->recv_lock, flags);
ppp_sync_input(ap, buf, cflags, count);
spin_unlock_irqrestore(&ap->recv_lock, flags);
if (!skb_queue_empty(&ap->rqueue))
tasklet_schedule(&ap->tsk);
sp_put(ap);
tty_unthrottle(tty);
}
static void
ppp_sync_wakeup(struct tty_struct *tty)
{
struct syncppp *ap = sp_get(tty);
clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
if (!ap)
return;
set_bit(XMIT_WAKEUP, &ap->xmit_flags);
tasklet_schedule(&ap->tsk);
sp_put(ap);
}
static struct tty_ldisc_ops ppp_sync_ldisc = {
.owner = THIS_MODULE,
.magic = TTY_LDISC_MAGIC,
.name = "pppsync",
.open = ppp_sync_open,
.close = ppp_sync_close,
.hangup = ppp_sync_hangup,
.read = ppp_sync_read,
.write = ppp_sync_write,
.ioctl = ppp_synctty_ioctl,
.poll = ppp_sync_poll,
.receive_buf = ppp_sync_receive,
.write_wakeup = ppp_sync_wakeup,
};
static int __init
ppp_sync_init(void)
{
int err;
err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
if (err != 0)
printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
err);
return err;
}
/*
* The following routines provide the PPP channel interface.
*/
static int
ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
{
struct syncppp *ap = chan->private;
int err, val;
u32 accm[8];
void __user *argp = (void __user *)arg;
u32 __user *p = argp;
err = -EFAULT;
switch (cmd) {
case PPPIOCGFLAGS:
val = ap->flags | ap->rbits;
if (put_user(val, (int __user *) argp))
break;
err = 0;
break;
case PPPIOCSFLAGS:
if (get_user(val, (int __user *) argp))
break;
ap->flags = val & ~SC_RCV_BITS;
spin_lock_irq(&ap->recv_lock);
ap->rbits = val & SC_RCV_BITS;
spin_unlock_irq(&ap->recv_lock);
err = 0;
break;
case PPPIOCGASYNCMAP:
if (put_user(ap->xaccm[0], p))
break;
err = 0;
break;
case PPPIOCSASYNCMAP:
if (get_user(ap->xaccm[0], p))
break;
err = 0;
break;
case PPPIOCGRASYNCMAP:
if (put_user(ap->raccm, p))
break;
err = 0;
break;
case PPPIOCSRASYNCMAP:
if (get_user(ap->raccm, p))
break;
err = 0;
break;
case PPPIOCGXASYNCMAP:
if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
break;
err = 0;
break;
case PPPIOCSXASYNCMAP:
if (copy_from_user(accm, argp, sizeof(accm)))
break;
accm[2] &= ~0x40000000U; /* can't escape 0x5e */
accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */
memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
err = 0;
break;
case PPPIOCGMRU:
if (put_user(ap->mru, (int __user *) argp))
break;
err = 0;
break;
case PPPIOCSMRU:
if (get_user(val, (int __user *) argp))
break;
if (val < PPP_MRU)
val = PPP_MRU;
ap->mru = val;
err = 0;
break;
default:
err = -ENOTTY;
}
return err;
}
/*
* This is called at softirq level to deliver received packets
* to the ppp_generic code, and to tell the ppp_generic code
* if we can accept more output now.
*/
static void ppp_sync_process(unsigned long arg)
{
struct syncppp *ap = (struct syncppp *) arg;
struct sk_buff *skb;
/* process received packets */
while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
if (skb->len == 0) {
/* zero length buffers indicate error */
ppp_input_error(&ap->chan, 0);
kfree_skb(skb);
}
else
ppp_input(&ap->chan, skb);
}
/* try to push more stuff out */
if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
ppp_output_wakeup(&ap->chan);
}
/*
* Procedures for encapsulation and framing.
*/
static struct sk_buff*
ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
{
int proto;
unsigned char *data;
int islcp;
data = skb->data;
proto = (data[0] << 8) + data[1];
/* LCP packets with codes between 1 (configure-request)
* and 7 (code-reject) must be sent as though no options
* have been negotiated.
*/
islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
/* compress protocol field if option enabled */
if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
skb_pull(skb,1);
/* prepend address/control fields if necessary */
if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
if (skb_headroom(skb) < 2) {
struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
if (npkt == NULL) {
kfree_skb(skb);
return NULL;
}
skb_reserve(npkt,2);
skb_copy_from_linear_data(skb,
skb_put(npkt, skb->len), skb->len);
kfree_skb(skb);
skb = npkt;
}
skb_push(skb,2);
skb->data[0] = PPP_ALLSTATIONS;
skb->data[1] = PPP_UI;
}
ap->last_xmit = jiffies;
if (skb && ap->flags & SC_LOG_OUTPKT)
ppp_print_buffer ("send buffer", skb->data, skb->len);
return skb;
}
/*
* Transmit-side routines.
*/
/*
* Send a packet to the peer over an sync tty line.
* Returns 1 iff the packet was accepted.
* If the packet was not accepted, we will call ppp_output_wakeup
* at some later time.
*/
static int
ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
{
struct syncppp *ap = chan->private;
ppp_sync_push(ap);
if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
return 0; /* already full */
skb = ppp_sync_txmunge(ap, skb);
if (skb != NULL)
ap->tpkt = skb;
else
clear_bit(XMIT_FULL, &ap->xmit_flags);
ppp_sync_push(ap);
return 1;
}
/*
* Push as much data as possible out to the tty.
*/
static int
ppp_sync_push(struct syncppp *ap)
{
int sent, done = 0;
struct tty_struct *tty = ap->tty;
int tty_stuffed = 0;
if (!spin_trylock_bh(&ap->xmit_lock))
return 0;
for (;;) {
if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
tty_stuffed = 0;
if (!tty_stuffed && ap->tpkt) {
set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
if (sent < 0)
goto flush; /* error, e.g. loss of CD */
if (sent < ap->tpkt->len) {
tty_stuffed = 1;
} else {
kfree_skb(ap->tpkt);
ap->tpkt = NULL;
clear_bit(XMIT_FULL, &ap->xmit_flags);
done = 1;
}
continue;
}
/* haven't made any progress */
spin_unlock_bh(&ap->xmit_lock);
if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
|| (!tty_stuffed && ap->tpkt)))
break;
if (!spin_trylock_bh(&ap->xmit_lock))
break;
}
return done;
flush:
if (ap->tpkt) {
kfree_skb(ap->tpkt);
ap->tpkt = NULL;
clear_bit(XMIT_FULL, &ap->xmit_flags);
done = 1;
}
spin_unlock_bh(&ap->xmit_lock);
return done;
}
/*
* Flush output from our internal buffers.
* Called for the TCFLSH ioctl.
*/
static void
ppp_sync_flush_output(struct syncppp *ap)
{
int done = 0;
spin_lock_bh(&ap->xmit_lock);
if (ap->tpkt != NULL) {
kfree_skb(ap->tpkt);
ap->tpkt = NULL;
clear_bit(XMIT_FULL, &ap->xmit_flags);
done = 1;
}
spin_unlock_bh(&ap->xmit_lock);
if (done)
ppp_output_wakeup(&ap->chan);
}
/*
* Receive-side routines.
*/
/* called when the tty driver has data for us.
*
* Data is frame oriented: each call to ppp_sync_input is considered
* a whole frame. If the 1st flag byte is non-zero then the whole
* frame is considered to be in error and is tossed.
*/
static void
ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
char *flags, int count)
{
struct sk_buff *skb;
unsigned char *p;
if (count == 0)
return;
if (ap->flags & SC_LOG_INPKT)
ppp_print_buffer ("receive buffer", buf, count);
/* stuff the chars in the skb */
skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
if (!skb) {
printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
goto err;
}
/* Try to get the payload 4-byte aligned */
if (buf[0] != PPP_ALLSTATIONS)
skb_reserve(skb, 2 + (buf[0] & 1));
if (flags && *flags) {
/* error flag set, ignore frame */
goto err;
} else if (count > skb_tailroom(skb)) {
/* packet overflowed MRU */
goto err;
}
p = skb_put(skb, count);
memcpy(p, buf, count);
/* strip address/control field if present */
p = skb->data;
if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
/* chop off address/control */
if (skb->len < 3)
goto err;
p = skb_pull(skb, 2);
}
/* decompress protocol field if compressed */
if (p[0] & 1) {
/* protocol is compressed */
skb_push(skb, 1)[0] = 0;
} else if (skb->len < 2)
goto err;
/* queue the frame to be processed */
skb_queue_tail(&ap->rqueue, skb);
return;
err:
/* queue zero length packet as error indication */
if (skb || (skb = dev_alloc_skb(0))) {
skb_trim(skb, 0);
skb_queue_tail(&ap->rqueue, skb);
}
}
static void __exit
ppp_sync_cleanup(void)
{
if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
}
module_init(ppp_sync_init);
module_exit(ppp_sync_cleanup);
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_SYNC_PPP);