-/* A simple network driver for lguest.
+/*D:500
+ * The Guest network driver.
*
- * Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
+ * This is very simple a virtual network driver, and our last Guest driver.
+ * The only trick is that it can talk directly to multiple other recipients
+ * (ie. other Guests on the same network). It can also be used with only the
+ * Host on the network.
+ :*/
+
+/* Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
*
* 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
#define MAX_LANS 4
#define NUM_SKBS 8
+/*M:011 Network code master Jeff Garzik points out numerous shortcomings in
+ * this driver if it aspires to greatness.
+ *
+ * Firstly, it doesn't use "NAPI": the networking's New API, and is poorer for
+ * it. As he says "NAPI means system-wide load leveling, across multiple
+ * network interfaces. Lack of NAPI can mean competition at higher loads."
+ *
+ * He also points out that we don't implement set_mac_address, so users cannot
+ * change the devices hardware address. When I asked why one would want to:
+ * "Bonding, and situations where you /do/ want the MAC address to "leak" out
+ * of the host onto the wider net."
+ *
+ * Finally, he would like module unloading: "It is not unrealistic to think of
+ * [un|re|]loading the net support module in an lguest guest. And, adding
+ * module support makes the programmer more responsible, because they now have
+ * to learn to clean up after themselves. Any driver that cannot clean up
+ * after itself is an incomplete driver in my book."
+ :*/
+
+/*D:530 The "struct lguestnet_info" contains all the information we need to
+ * know about the network device. */
struct lguestnet_info
{
- /* The shared page(s). */
+ /* The mapped device page(s) (an array of "struct lguest_net"). */
struct lguest_net *peer;
+ /* The physical address of the device page(s) */
unsigned long peer_phys;
+ /* The size of the device page(s). */
unsigned long mapsize;
/* The lguest_device I come from */
struct lguest_device *lgdev;
- /* My peerid. */
+ /* My peerid (ie. my slot in the array). */
unsigned int me;
- /* Receive queue. */
+ /* Receive queue: the network packets waiting to be filled. */
struct sk_buff *skb[NUM_SKBS];
struct lguest_dma dma[NUM_SKBS];
};
+/*:*/
/* How many bytes left in this page. */
static unsigned int rest_of_page(void *data)
return PAGE_SIZE - ((unsigned long)data % PAGE_SIZE);
}
-/* Simple convention: offset 4 * peernum. */
+/*D:570 Each peer (ie. Guest or Host) on the network binds their receive
+ * buffers to a different key: we simply use the physical address of the
+ * device's memory page plus the peer number. The Host insists that all keys
+ * be a multiple of 4, so we multiply the peer number by 4. */
static unsigned long peer_key(struct lguestnet_info *info, unsigned peernum)
{
return info->peer_phys + 4 * peernum;
}
+/* This is the routine which sets up a "struct lguest_dma" to point to a
+ * network packet, similar to req_to_dma() in lguest_blk.c. The structure of a
+ * "struct sk_buff" has grown complex over the years: it consists of a "head"
+ * linear section pointed to by "skb->data", and possibly an array of
+ * "fragments" in the case of a non-linear packet.
+ *
+ * Our receive buffers don't use fragments at all but outgoing skbs might, so
+ * we handle it. */
static void skb_to_dma(const struct sk_buff *skb, unsigned int headlen,
struct lguest_dma *dma)
{
unsigned int i, seg;
+ /* First, we put the linear region into the "struct lguest_dma". Each
+ * entry can't go over a page boundary, so even though all our packets
+ * are 1514 bytes or less, we might need to use two entries here: */
for (i = seg = 0; i < headlen; seg++, i += rest_of_page(skb->data+i)) {
dma->addr[seg] = virt_to_phys(skb->data + i);
dma->len[seg] = min((unsigned)(headlen - i),
rest_of_page(skb->data + i));
}
+
+ /* Now we handle the fragments: at least they're guaranteed not to go
+ * over a page. skb_shinfo(skb) returns a pointer to the structure
+ * which tells us about the number of fragments and the fragment
+ * array. */
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++, seg++) {
const skb_frag_t *f = &skb_shinfo(skb)->frags[i];
/* Should not happen with MTU less than 64k - 2 * PAGE_SIZE. */
if (seg == LGUEST_MAX_DMA_SECTIONS) {
+ /* We will end up sending a truncated packet should
+ * this ever happen. Plus, a cool log message! */
printk("Woah dude! Megapacket!\n");
break;
}
dma->addr[seg] = page_to_phys(f->page) + f->page_offset;
dma->len[seg] = f->size;
}
+
+ /* If after all that we didn't use the entire "struct lguest_dma"
+ * array, we terminate it with a 0 length. */
if (seg < LGUEST_MAX_DMA_SECTIONS)
dma->len[seg] = 0;
}
-/* We overload multicast bit to show promiscuous mode. */
+/*
+ * Packet transmission.
+ *
+ * Our packet transmission is a little unusual. A real network card would just
+ * send out the packet and leave the receivers to decide if they're interested.
+ * Instead, we look through the network device memory page and see if any of
+ * the ethernet addresses match the packet destination, and if so we send it to
+ * that Guest.
+ *
+ * This is made a little more complicated in two cases. The first case is
+ * broadcast packets: for that we send the packet to all Guests on the network,
+ * one at a time. The second case is "promiscuous" mode, where a Guest wants
+ * to see all the packets on the network. We need a way for the Guest to tell
+ * us it wants to see all packets, so it sets the "multicast" bit on its
+ * published MAC address, which is never valid in a real ethernet address.
+ */
#define PROMISC_BIT 0x01
+/* This is the callback which is summoned whenever the network device's
+ * multicast or promiscuous state changes. If the card is in promiscuous mode,
+ * we advertise that in our ethernet address in the device's memory. We do the
+ * same if Linux wants any or all multicast traffic. */
static void lguestnet_set_multicast(struct net_device *dev)
{
struct lguestnet_info *info = netdev_priv(dev);
info->peer[info->me].mac[0] &= ~PROMISC_BIT;
}
+/* A simple test function to see if a peer wants to see all packets.*/
static int promisc(struct lguestnet_info *info, unsigned int peer)
{
return info->peer[peer].mac[0] & PROMISC_BIT;
}
+/* Another simple function to see if a peer's advertised ethernet address
+ * matches a packet's destination ethernet address. */
static int mac_eq(const unsigned char mac[ETH_ALEN],
struct lguestnet_info *info, unsigned int peer)
{
return memcmp(mac+1, info->peer[peer].mac+1, ETH_ALEN-1) == 0;
}
+/* This is the function which actually sends a packet once we've decided a
+ * peer wants it: */
static void transfer_packet(struct net_device *dev,
struct sk_buff *skb,
unsigned int peernum)
struct lguestnet_info *info = netdev_priv(dev);
struct lguest_dma dma;
+ /* We use our handy "struct lguest_dma" packing function to prepare
+ * the skb for sending. */
skb_to_dma(skb, skb_headlen(skb), &dma);
pr_debug("xfer length %04x (%u)\n", htons(skb->len), skb->len);
+ /* This is the actual send call which copies the packet. */
lguest_send_dma(peer_key(info, peernum), &dma);
+
+ /* Check that the entire packet was transmitted. If not, it could mean
+ * that the other Guest registered a short receive buffer, but this
+ * driver should never do that. More likely, the peer is dead. */
if (dma.used_len != skb->len) {
dev->stats.tx_carrier_errors++;
pr_debug("Bad xfer to peer %i: %i of %i (dma %p/%i)\n",
peernum, dma.used_len, skb->len,
(void *)dma.addr[0], dma.len[0]);
} else {
+ /* On success we update the stats. */
dev->stats.tx_bytes += skb->len;
dev->stats.tx_packets++;
}
}
+/* Another helper function to tell is if a slot in the device memory is unused.
+ * Since we always set the Local Assignment bit in the ethernet address, the
+ * first byte can never be 0. */
static int unused_peer(const struct lguest_net peer[], unsigned int num)
{
return peer[num].mac[0] == 0;
}
+/* Finally, here is the routine which handles an outgoing packet. It's called
+ * "start_xmit" for traditional reasons. */
static int lguestnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
unsigned int i;
int broadcast;
struct lguestnet_info *info = netdev_priv(dev);
+ /* Extract the destination ethernet address from the packet. */
const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
+ DECLARE_MAC_BUF(mac);
- pr_debug("%s: xmit %02x:%02x:%02x:%02x:%02x:%02x\n",
- dev->name, dest[0],dest[1],dest[2],dest[3],dest[4],dest[5]);
+ pr_debug("%s: xmit %s\n", dev->name, print_mac(mac, dest));
+ /* If it's a multicast packet, we broadcast to everyone. That's not
+ * very efficient, but there are very few applications which actually
+ * use multicast, which is a shame really.
+ *
+ * As etherdevice.h points out: "By definition the broadcast address is
+ * also a multicast address." So we don't have to test for broadcast
+ * packets separately. */
broadcast = is_multicast_ether_addr(dest);
+
+ /* Look through all the published ethernet addresses to see if we
+ * should send this packet. */
for (i = 0; i < info->mapsize/sizeof(struct lguest_net); i++) {
+ /* We don't send to ourselves (we actually can't SEND_DMA to
+ * ourselves anyway), and don't send to unused slots.*/
if (i == info->me || unused_peer(info->peer, i))
continue;
+ /* If it's broadcast we send it. If they want every packet we
+ * send it. If the destination matches their address we send
+ * it. Otherwise we go to the next peer. */
if (!broadcast && !promisc(info, i) && !mac_eq(dest, info, i))
continue;
pr_debug("lguestnet %s: sending from %i to %i\n",
dev->name, info->me, i);
+ /* Our routine which actually does the transfer. */
transfer_packet(dev, skb, i);
}
+
+ /* An xmit routine is expected to dispose of the packet, so we do. */
dev_kfree_skb(skb);
+
+ /* As per kernel convention, 0 means success. This is why I love
+ * networking: even if we never sent to anyone, that's still
+ * success! */
return 0;
}
-/* Find a new skb to put in this slot in shared mem. */
+/*D:560
+ * Packet receiving.
+ *
+ * First, here's a helper routine which fills one of our array of receive
+ * buffers: */
static int fill_slot(struct net_device *dev, unsigned int slot)
{
struct lguestnet_info *info = netdev_priv(dev);
- /* Try to create and register a new one. */
+
+ /* We can receive ETH_DATA_LEN (1500) byte packets, plus a standard
+ * ethernet header of ETH_HLEN (14) bytes. */
info->skb[slot] = netdev_alloc_skb(dev, ETH_HLEN + ETH_DATA_LEN);
if (!info->skb[slot]) {
printk("%s: could not fill slot %i\n", dev->name, slot);
return -ENOMEM;
}
+ /* skb_to_dma() is a helper which sets up the "struct lguest_dma" to
+ * point to the data in the skb: we also use it for sending out a
+ * packet. */
skb_to_dma(info->skb[slot], ETH_HLEN + ETH_DATA_LEN, &info->dma[slot]);
+
+ /* This is a Write Memory Barrier: it ensures that the entry in the
+ * receive buffer array is written *before* we set the "used_len" entry
+ * to 0. If the Host were looking at the receive buffer array from a
+ * different CPU, it could potentially see "used_len = 0" and not see
+ * the updated receive buffer information. This would be a horribly
+ * nasty bug, so make sure the compiler and CPU know this has to happen
+ * first. */
wmb();
- /* Now we tell hypervisor it can use the slot. */
+ /* Writing 0 to "used_len" tells the Host it can use this receive
+ * buffer now. */
info->dma[slot].used_len = 0;
return 0;
}
+/* This is the actual receive routine. When we receive an interrupt from the
+ * Host to tell us a packet has been delivered, we arrive here: */
static irqreturn_t lguestnet_rcv(int irq, void *dev_id)
{
struct net_device *dev = dev_id;
struct lguestnet_info *info = netdev_priv(dev);
unsigned int i, done = 0;
+ /* Look through our entire receive array for an entry which has data
+ * in it. */
for (i = 0; i < ARRAY_SIZE(info->dma); i++) {
unsigned int length;
struct sk_buff *skb;
if (length == 0)
continue;
+ /* We've found one! Remember the skb (we grabbed the length
+ * above), and immediately refill the slot we've taken it
+ * from. */
done++;
skb = info->skb[i];
fill_slot(dev, i);
+ /* This shouldn't happen: micropackets could be sent by a
+ * badly-behaved Guest on the network, but the Host will never
+ * stuff more data in the buffer than the buffer length. */
if (length < ETH_HLEN || length > ETH_HLEN + ETH_DATA_LEN) {
pr_debug(KERN_WARNING "%s: unbelievable skb len: %i\n",
dev->name, length);
continue;
}
+ /* skb_put(), what a great function! I've ranted about this
+ * function before (http://lkml.org/lkml/1999/9/26/24). You
+ * call it after you've added data to the end of an skb (in
+ * this case, it was the Host which wrote the data). */
skb_put(skb, length);
+
+ /* The ethernet header contains a protocol field: we use the
+ * standard helper to extract it, and place the result in
+ * skb->protocol. The helper also sets up skb->pkt_type and
+ * eats up the ethernet header from the front of the packet. */
skb->protocol = eth_type_trans(skb, dev);
- /* This is a reliable transport. */
+
+ /* If this device doesn't need checksums for sending, we also
+ * don't need to check the packets when they come in. */
if (dev->features & NETIF_F_NO_CSUM)
skb->ip_summed = CHECKSUM_UNNECESSARY;
+
+ /* As a last resort for debugging the driver or the lguest I/O
+ * subsystem, you can uncomment the "#define DEBUG" at the top
+ * of this file, which turns all the pr_debug() into printk()
+ * and floods the logs. */
pr_debug("Receiving skb proto 0x%04x len %i type %i\n",
ntohs(skb->protocol), skb->len, skb->pkt_type);
+ /* Update the packet and byte counts (visible from ifconfig,
+ * and good for debugging). */
dev->stats.rx_bytes += skb->len;
dev->stats.rx_packets++;
+
+ /* Hand our fresh network packet into the stack's "network
+ * interface receive" routine. That will free the packet
+ * itself when it's finished. */
netif_rx(skb);
}
+
+ /* If we found any packets, we assume the interrupt was for us. */
return done ? IRQ_HANDLED : IRQ_NONE;
}
+/*D:550 This is where we start: when the device is brought up by dhcpd or
+ * ifconfig. At this point we advertise our MAC address to the rest of the
+ * network, and register receive buffers ready for incoming packets. */
static int lguestnet_open(struct net_device *dev)
{
int i;
struct lguestnet_info *info = netdev_priv(dev);
- /* Set up our MAC address */
+ /* Copy our MAC address into the device page, so others on the network
+ * can find us. */
memcpy(info->peer[info->me].mac, dev->dev_addr, ETH_ALEN);
- /* Turn on promisc mode if needed */
+ /* We might already be in promisc mode (dev->flags & IFF_PROMISC). Our
+ * set_multicast callback handles this already, so we call it now. */
lguestnet_set_multicast(dev);
+ /* Allocate packets and put them into our "struct lguest_dma" array.
+ * If we fail to allocate all the packets we could still limp along,
+ * but it's a sign of real stress so we should probably give up now. */
for (i = 0; i < ARRAY_SIZE(info->dma); i++) {
if (fill_slot(dev, i) != 0)
goto cleanup;
}
+
+ /* Finally we tell the Host where our array of "struct lguest_dma"
+ * receive buffers is, binding it to the key corresponding to the
+ * device's physical memory plus our peerid. */
if (lguest_bind_dma(peer_key(info,info->me), info->dma,
NUM_SKBS, lgdev_irq(info->lgdev)) != 0)
goto cleanup;
dev_kfree_skb(info->skb[i]);
return -ENOMEM;
}
+/*:*/
+/* The close routine is called when the device is no longer in use: we clean up
+ * elegantly. */
static int lguestnet_close(struct net_device *dev)
{
unsigned int i;
struct lguestnet_info *info = netdev_priv(dev);
- /* Clear all trace: others might deliver packets, we'll ignore it. */
+ /* Clear all trace of our existence out of the device memory by setting
+ * the slot which held our MAC address to 0 (unused). */
memset(&info->peer[info->me], 0, sizeof(info->peer[info->me]));
- /* Deregister sg lists. */
+ /* Unregister our array of receive buffers */
lguest_unbind_dma(peer_key(info, info->me), info->dma);
for (i = 0; i < ARRAY_SIZE(info->dma); i++)
dev_kfree_skb(info->skb[i]);
return 0;
}
+/*D:510 The network device probe function is basically a standard ethernet
+ * device setup. It reads the "struct lguest_device_desc" and sets the "struct
+ * net_device". Oh, the line-by-line excitement! Let's skip over it. :*/
static int lguestnet_probe(struct lguest_device *lgdev)
{
int err, irqf = IRQF_SHARED;
if (!dev)
return -ENOMEM;
- SET_MODULE_OWNER(dev);
-
/* Ethernet defaults with some changes */
ether_setup(dev);
dev->set_mac_address = NULL;
dev->stop = lguestnet_close;
dev->hard_start_xmit = lguestnet_start_xmit;
- /* Turning on/off promisc will call dev->set_multicast_list.
- * We don't actually support multicast yet */
+ /* We don't actually support multicast yet, but turning on/off
+ * promisc also calls dev->set_multicast_list. */
dev->set_multicast_list = lguestnet_set_multicast;
SET_NETDEV_DEV(dev, &lgdev->dev);
+
+ /* The network code complains if you have "scatter-gather" capability
+ * if you don't also handle checksums (it seem that would be
+ * "illogical"). So we use a lie of omission and don't tell it that we
+ * can handle scattered packets unless we also don't want checksums,
+ * even though to us they're completely independent. */
if (desc->features & LGUEST_NET_F_NOCSUM)
dev->features = NETIF_F_SG|NETIF_F_NO_CSUM;
}
pr_debug("lguestnet: registered device %s\n", dev->name);
+ /* Finally, we put the "struct net_device" in the generic "struct
+ * lguest_device"s private pointer. Again, it's not necessary, but
+ * makes sure the cool kernel kids don't tease us. */
lgdev->private = dev;
return 0;
MODULE_DESCRIPTION("Lguest network driver");
MODULE_LICENSE("GPL");
+
+/*D:580
+ * This is the last of the Drivers, and with this we have covered the many and
+ * wonderous and fine (and boring) details of the Guest.
+ *
+ * "make Launcher" beckons, where we answer questions like "Where do Guests
+ * come from?", and "What do you do when someone asks for optimization?"
+ */
git.openpandora.org / pandora-kernel.git / blobdiff