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[minix3.git] / minix / net / lwip / loopif.c

/* LWIP service - loopif.c - loopback interfaces */
/*
 * There is always at least one loopback device.  This device is used also to
 * loop back packets sent on other interfaces to the local interface address.
 * Therefore, not all packets on the loopback device have a source or
 * destination address corresponding to the loopback device.
 */

#include "lwip.h"

/*
 * As a safety measure, if lwIP somehow gets stuck in a loop replying to its
 * own packets on a loopback interface, stop with immediately feeding packets
 * back into lwIP after this many packets.  The remaining packets will still be
 * delivered, but not before the main message loop has had a chance to run.
 */
#define LOOPIF_LIMIT    65536

/*
 * The MTU is restricted to 65531 bytes, because we need space for a 4-byte
 * header to identify the original interface of the packet.
 */
#define LOOPIF_MAX_MTU  (UINT16_MAX - sizeof(uint32_t)) /* maximum MTU */
#define LOOPIF_DEF_MTU  LOOPIF_MAX_MTU                  /* default MTU */

#define NR_LOOPIF       2               /* number of loopback devices */

struct loopif {
        struct ifdev loopif_ifdev;      /* interface device, MUST be first */
        struct pbuf *loopif_head;       /* head of pending loopback packets */
        struct pbuf **loopif_tailp;     /* tail ptr-ptr of pending packets */
        TAILQ_ENTRY(loopif) loopif_next;        /* next in free list */
} loopif_array[NR_LOOPIF];

static TAILQ_HEAD(, loopif) loopif_freelist;    /* free loop interfaces list */
static TAILQ_HEAD(, loopif) loopif_activelist;  /* active loop interfaces */

#define loopif_get_netif(loopif) (ifdev_get_netif(&(loopif)->loopif_ifdev))

static unsigned int loopif_cksum_flags;

static int loopif_create(const char *name);

static const struct ifdev_ops loopif_ops;

/*
 * Initialize the loopback interface module.
 */
void
loopif_init(void)
{
        unsigned int slot;

        /* Initialize the lists of loopback interfaces. */
        TAILQ_INIT(&loopif_freelist);
        TAILQ_INIT(&loopif_activelist);

        for (slot = 0; slot < __arraycount(loopif_array); slot++)
                TAILQ_INSERT_TAIL(&loopif_freelist, &loopif_array[slot],
                    loopif_next);

        /*
         * The default is to perform no checksumming on loopback interfaces,
         * except for ICMP messages because otherwise we would need additional
         * changes in the code receiving those.  In fact, for future
         * compatibility, disable only those flags that we manage ourselves.
         */
        loopif_cksum_flags = NETIF_CHECKSUM_ENABLE_ALL &
            ~(NETIF_CHECKSUM_GEN_IP | NETIF_CHECKSUM_CHECK_IP |
            NETIF_CHECKSUM_GEN_UDP | NETIF_CHECKSUM_CHECK_UDP |
            NETIF_CHECKSUM_GEN_TCP | NETIF_CHECKSUM_CHECK_TCP);

        /* Tell the ifdev module that users may create more loopif devices. */
        ifdev_register("lo", loopif_create);
}

/*
 * Polling function, invoked after each message loop iteration.  Forward any
 * packets received on the output side of the loopback device during this
 * loop iteration, to the input side of the device.
 */
static void
loopif_poll(struct ifdev * ifdev)
{
        struct loopif *loopif = (struct loopif *)ifdev;
        struct pbuf *pbuf, **pnext;
        struct ifdev *oifdev;
        struct netif *netif;
        uint32_t oifindex;
        unsigned int count;
        static int warned = FALSE;

        count = 0;

        while ((pbuf = loopif->loopif_head) != NULL) {
                /*
                 * Prevent endless loops.  Keep in mind that packets may be
                 * added to the queue as part of processing packets from the
                 * queue here, so the queue itself will never reach this
                 * length.  As such the limit can (and must) be fairly high.
                 *
                 * In any case, if this warning is shown, that basically means
                 * that a bug in lwIP has been triggered.  There should be no
                 * such bugs, so if there are, they should be fixed in lwIP.
                 */
                if (count++ == LOOPIF_LIMIT) {
                        if (!warned) {
                                printf("LWIP: excess loopback traffic, "
                                    "throttling output\n");
                                warned = TRUE;
                        }

                        break;
                }

                pnext = pchain_end(pbuf);

                if ((loopif->loopif_head = *pnext) == NULL)
                        loopif->loopif_tailp = &loopif->loopif_head;
                *pnext = NULL;

                /*
                 * Get the original interface for the packet, which if non-zero
                 * must also be used to pass the packet back to.  The interface
                 * should still exist in all cases, but better safe than sorry.
                 */
                memcpy(&oifindex, pbuf->payload, sizeof(oifindex));

                util_pbuf_header(pbuf, -(int)sizeof(oifindex));

                if (oifindex != 0 &&
                    (oifdev = ifdev_get_by_index(oifindex)) != NULL)
                        netif = ifdev_get_netif(oifdev);
                else
                        netif = NULL;

                /*
                 * Loopback devices hand packets to BPF on output only.  Doing
                 * so on input as well would duplicate all captured packets.
                 */
                ifdev_input(ifdev, pbuf, netif, FALSE /*to_bpf*/);
        }
}

/*
 * Process a packet as output on a loopback interface.  Packets cannot be
 * passed back into lwIP right away, nor can the original packets be passed
 * back into lwIP.  Therefore, make a copy of the packet, and pass it back to
 * lwIP at the end of the current message loop iteration.
 */
static err_t
loopif_output(struct ifdev * ifdev, struct pbuf * pbuf, struct netif * netif)
{
        struct loopif *loopif = (struct loopif *)ifdev;
        struct ifdev *oifdev;
        struct pbuf *pcopy;
        uint32_t oifindex;

        /* Reject oversized packets immediately.  This should not happen. */
        if (pbuf->tot_len > UINT16_MAX - sizeof(oifindex)) {
                printf("LWIP: attempt to send oversized loopback packet\n");

                return ERR_MEM;
        }

        /*
         * If the service is low on memory, this is a likely place where
         * allocation failures will occur.  Thus, do not print anything here.
         * The user can diagnose such problems with interface statistics.
         */
        pcopy = pchain_alloc(PBUF_RAW, sizeof(oifindex) + pbuf->tot_len);
        if (pcopy == NULL) {
                ifdev_output_drop(ifdev);

                return ERR_MEM;
        }

        /*
         * If the packet was purposely diverted from a non-loopback interface
         * to this interface, we have to remember the original interface, so
         * that we can pass back the packet to that interface as well.  If we
         * don't, packets to link-local addresses assigned to non-loopback
         * interfaces will not be processed correctly.
         */
        if (netif != NULL) {
                oifdev = netif_get_ifdev(netif);
                oifindex = ifdev_get_index(oifdev);
        } else
                oifindex = 0;

        assert(pcopy->len >= sizeof(oifindex));

        memcpy(pcopy->payload, &oifindex, sizeof(oifindex));

        util_pbuf_header(pcopy, -(int)sizeof(oifindex));

        if (pbuf_copy(pcopy, pbuf) != ERR_OK)
                panic("unexpected pbuf copy failure");

        pcopy->flags |= pbuf->flags & (PBUF_FLAG_LLMCAST | PBUF_FLAG_LLBCAST);

        util_pbuf_header(pcopy, sizeof(oifindex));

        *loopif->loopif_tailp = pcopy;
        loopif->loopif_tailp = pchain_end(pcopy);

        return ERR_OK;
}

/*
 * Initialization function for a loopback-type netif interface, called from
 * lwIP at interface creation time.
 */
static err_t
loopif_init_netif(struct ifdev * ifdev, struct netif * netif)
{

        netif->name[0] = 'l';
        netif->name[1] = 'o';

        /*
         * FIXME: unfortunately, lwIP does not allow one to enable multicast on
         * an interface without also enabling multicast management traffic
         * (that is, IGMP and MLD).  Thus, for now, joining multicast groups
         * and assigning local IPv6 addresses will incur such traffic even on
         * loopback interfaces.  For now this is preferable over not supporting
         * multicast on loopback interfaces at all.
         */
        netif->flags |= NETIF_FLAG_IGMP | NETIF_FLAG_MLD6;

        NETIF_SET_CHECKSUM_CTRL(netif, loopif_cksum_flags);

        return ERR_OK;
}

/*
 * Create a new loopback device.
 */
static int
loopif_create(const char * name)
{
        struct loopif *loopif;

        /* Find a free loopback interface slot, if available. */
        if (TAILQ_EMPTY(&loopif_freelist))
                return ENOBUFS;

        loopif = TAILQ_FIRST(&loopif_freelist);
        TAILQ_REMOVE(&loopif_freelist, loopif, loopif_next);

        /* Initialize the loopif structure. */
        TAILQ_INSERT_HEAD(&loopif_activelist, loopif, loopif_next);

        loopif->loopif_head = NULL;
        loopif->loopif_tailp = &loopif->loopif_head;

        /*
         * For simplicity and efficiency, we do not prepend the address family
         * (IPv4/IPv6) to the packet for BPF, which means our loopback devices
         * are of type DLT_RAW rather than (NetBSD's) DLT_NULL.
         */
        ifdev_add(&loopif->loopif_ifdev, name, IFF_LOOPBACK | IFF_MULTICAST,
            IFT_LOOP, 0 /*hdrlen*/, 0 /*addrlen*/, DLT_RAW, LOOPIF_MAX_MTU,
            0 /*nd6flags*/, &loopif_ops);

        ifdev_update_link(&loopif->loopif_ifdev, LINK_STATE_UP);

        return OK;
}

/*
 * Destroy an existing loopback device.
 */
static int
loopif_destroy(struct ifdev * ifdev)
{
        struct loopif *loopif = (struct loopif *)ifdev;
        struct pbuf *pbuf, **pnext;
        int r;

        /*
         * The ifdev module may refuse to remove this interface if it is the
         * loopback interface used to loop back packets for other interfaces.
         */
        if ((r = ifdev_remove(&loopif->loopif_ifdev)) != OK)
                return r;

        /*
         * Clean up.  The loopback queue can be non-empty only if we have been
         * throttling in case of a feedback loop.
         */
        while ((pbuf = loopif->loopif_head) != NULL) {
                pnext = pchain_end(pbuf);

                if ((loopif->loopif_head = *pnext) == NULL)
                        loopif->loopif_tailp = &loopif->loopif_head;
                *pnext = NULL;

                pbuf_free(pbuf);
        }

        TAILQ_REMOVE(&loopif_activelist, loopif, loopif_next);

        TAILQ_INSERT_HEAD(&loopif_freelist, loopif, loopif_next);

        return OK;
}

/*
 * Set NetBSD-style interface flags (IFF_) for a loopback interface.
 */
static int
loopif_set_ifflags(struct ifdev * ifdev, unsigned int ifflags)
{
        struct loopif *loopif = (struct loopif *)ifdev;

        /*
         * Only the IFF_UP flag may be set and cleared.  We adjust the
         * IFF_RUNNING flag immediately based on this flag.  This is a bit
         * dangerous, but the caller takes this possibility into account.
         */
        if ((ifflags & ~IFF_UP) != 0)
                return EINVAL;

        if (ifflags & IFF_UP)
                ifdev_update_ifflags(&loopif->loopif_ifdev,
                    ifdev_get_ifflags(&loopif->loopif_ifdev) | IFF_RUNNING);
        else
                ifdev_update_ifflags(&loopif->loopif_ifdev,
                    ifdev_get_ifflags(&loopif->loopif_ifdev) & ~IFF_RUNNING);

        return OK;
}

/*
 * Set the Maximum Transmission Unit for this interface.  Return TRUE if the
 * new value is acceptable, in which case the caller will do the rest.  Return
 * FALSE otherwise.
 */
static int
loopif_set_mtu(struct ifdev * ifdev __unused, unsigned int mtu)
{

        return (mtu <= LOOPIF_MAX_MTU);
}

static const struct ifdev_ops loopif_ops = {
        .iop_init = loopif_init_netif,
        .iop_input = ip_input,
        .iop_output = loopif_output,
        .iop_poll = loopif_poll,
        .iop_set_ifflags = loopif_set_ifflags,
        .iop_set_mtu = loopif_set_mtu,
        .iop_destroy = loopif_destroy,
};

/*
 * Set and/or retrieve a per-protocol loopback checksumming option through
 * sysctl(7).
 */
ssize_t
loopif_cksum(struct rmib_call * call, struct rmib_node * node __unused,
        struct rmib_oldp * oldp, struct rmib_newp * newp)
{
        struct loopif *loopif;
        unsigned int flags;
        int r, val;

        /*
         * The third name field is the protocol.  We ignore the domain (the
         * second field), thus sharing settings between PF_INET and PF_INET6.
         * This is necessary because lwIP does not support TCP/UDP checksumming
         * flags on a per-domain basis.
         */
        switch (call->call_oname[2]) {
        case IPPROTO_IP:
                flags = NETIF_CHECKSUM_GEN_IP | NETIF_CHECKSUM_CHECK_IP;
                break;
        case IPPROTO_UDP:
                flags = NETIF_CHECKSUM_GEN_UDP | NETIF_CHECKSUM_CHECK_UDP;
                break;
        case IPPROTO_TCP:
                flags = NETIF_CHECKSUM_GEN_TCP | NETIF_CHECKSUM_CHECK_TCP;
                break;
        default:
                return EINVAL;
        }

        /* Copy out the old (current) checksumming option. */
        if (oldp != NULL) {
                val = !!(loopif_cksum_flags & flags);

                if ((r = rmib_copyout(oldp, 0, &val, sizeof(val))) < 0)
                        return r;
        }

        if (newp != NULL) {
                if ((r = rmib_copyin(newp, &val, sizeof(val))) != OK)
                        return r;

                if (val)
                        loopif_cksum_flags |= flags;
                else
                        loopif_cksum_flags &= ~flags;

                /*
                 * Apply the new checksum flags to all loopback interfaces.
                 * Technically, this may result in dropped packets when
                 * enabling checksumming on a throttled loopif, but that is a
                 * case so rare and unimportant that we ignore it.
                 */
                TAILQ_FOREACH(loopif, &loopif_activelist, loopif_next) {
                        NETIF_SET_CHECKSUM_CTRL(loopif_get_netif(loopif),
                            loopif_cksum_flags);
                }
        }

        /* Return the length of the node. */
        return sizeof(val);
}