diff options
Diffstat (limited to 'drivers/net/lguest_net.c')
| -rw-r--r-- | drivers/net/lguest_net.c | 218 |
1 files changed, 201 insertions, 17 deletions
diff --git a/drivers/net/lguest_net.c b/drivers/net/lguest_net.c index 112778652f7..20df6a84892 100644 --- a/drivers/net/lguest_net.c +++ b/drivers/net/lguest_net.c @@ -1,6 +1,13 @@ -/* 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 @@ -28,23 +35,28 @@ #define MAX_LANS 4 #define NUM_SKBS 8 +/*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) @@ -52,39 +64,82 @@ 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); @@ -95,11 +150,14 @@ static void lguestnet_set_multicast(struct net_device *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) { @@ -109,6 +167,8 @@ static int mac_eq(const unsigned char mac[ETH_ALEN], 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) @@ -116,76 +176,134 @@ static void transfer_packet(struct net_device *dev, 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; 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]); + /* 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; @@ -194,10 +312,16 @@ static irqreturn_t lguestnet_rcv(int irq, void *dev_id) 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); @@ -205,36 +329,72 @@ static irqreturn_t lguestnet_rcv(int irq, void *dev_id) 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; @@ -245,22 +405,29 @@ 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; @@ -290,10 +457,16 @@ static int lguestnet_probe(struct lguest_device *lgdev) 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; @@ -325,6 +498,9 @@ static int lguestnet_probe(struct lguest_device *lgdev) } 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; @@ -352,3 +528,11 @@ module_init(lguestnet_init); 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?" + */ |