path: root/src/VBox/NetworkServices/NAT/proxy_pollmgr.c

/* -*- indent-tabs-mode: nil; -*- */
#include "winutils.h"

#include "proxy_pollmgr.h"
#include "proxy.h"

#ifndef RT_OS_WINDOWS
#include <sys/socket.h>
#include <netinet/in.h>
#include <err.h>
#include <errno.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#else
#include <iprt/err.h>
#include <stdlib.h>
#include <string.h>
#include "winpoll.h"
#endif

#define POLLMGR_GARBAGE (-1)

struct pollmgr {
    struct pollfd *fds;
    struct pollmgr_handler **handlers;
    nfds_t capacity;            /* allocated size of the arrays */
    nfds_t nfds;                /* part of the arrays in use */

    /* channels (socketpair) for static slots */
    SOCKET chan[POLLMGR_SLOT_STATIC_COUNT][2];
#define POLLMGR_CHFD_RD 0       /* - pollmgr side */
#define POLLMGR_CHFD_WR 1       /* - client side */
} pollmgr;


static void pollmgr_loop(void);

static void pollmgr_add_at(int, struct pollmgr_handler *, SOCKET, int);
static void pollmgr_refptr_delete(struct pollmgr_refptr *);


/*
 * We cannot portably peek at the length of the incoming datagram and
 * pre-allocate pbuf chain to recvmsg() directly to it.  On Linux it's
 * possible to recv with MSG_PEEK|MSG_TRUC, but extra syscall is
 * probably more expensive (haven't measured) than doing an extra copy
 * of data, since typical UDP datagrams are small enough to avoid
 * fragmentation.
 *
 * We can use shared buffer here since we read from sockets
 * sequentially in a loop over pollfd.
 */
u8_t pollmgr_udpbuf[64 * 1024];


int
pollmgr_init(void)
{
    struct pollfd *newfds;
    struct pollmgr_handler **newhdls;
    nfds_t newcap;
    int status;
    nfds_t i;

    pollmgr.fds = NULL;
    pollmgr.handlers = NULL;
    pollmgr.capacity = 0;
    pollmgr.nfds = 0;

    for (i = 0; i < POLLMGR_SLOT_STATIC_COUNT; ++i) {
        pollmgr.chan[i][POLLMGR_CHFD_RD] = -1;
        pollmgr.chan[i][POLLMGR_CHFD_WR] = -1;
    }

    for (i = 0; i < POLLMGR_SLOT_STATIC_COUNT; ++i) {
#ifndef RT_OS_WINDOWS
        status = socketpair(PF_LOCAL, SOCK_DGRAM, 0, pollmgr.chan[i]);
        if (status < 0) {
            perror("socketpair");
            goto cleanup_close;
        }
#else
        status = RTWinSocketPair(PF_INET, SOCK_DGRAM, 0, pollmgr.chan[i]);
        AssertRCReturn(status, -1);

        if (RT_FAILURE(status)) {
            perror("socketpair");
            goto cleanup_close;
        }
#endif
    }


    newcap = 16;                /* XXX: magic */
    LWIP_ASSERT1(newcap >= POLLMGR_SLOT_STATIC_COUNT);

    newfds = (struct pollfd *)
        malloc(newcap * sizeof(*pollmgr.fds));
    if (newfds == NULL) {
        perror("calloc");
        goto cleanup_close;
    }

    newhdls = (struct pollmgr_handler **)
        malloc(newcap * sizeof(*pollmgr.handlers));
    if (newhdls == NULL) {
        perror("malloc");
        free(newfds);
        goto cleanup_close;
    }

    pollmgr.capacity = newcap;
    pollmgr.fds = newfds;
    pollmgr.handlers = newhdls;

    pollmgr.nfds = POLLMGR_SLOT_STATIC_COUNT;

    for (i = 0; i < pollmgr.capacity; ++i) {
        pollmgr.fds[i].fd = INVALID_SOCKET;
        pollmgr.fds[i].events = 0;
        pollmgr.fds[i].revents = 0;
    }

    return 0;

  cleanup_close:
    for (i = 0; i < POLLMGR_SLOT_STATIC_COUNT; ++i) {
        SOCKET *chan = pollmgr.chan[i];
        if (chan[POLLMGR_CHFD_RD] >= 0) {
            closesocket(chan[POLLMGR_CHFD_RD]);
            closesocket(chan[POLLMGR_CHFD_WR]);
        }
    }

    return -1;
}


/*
 * Must be called before pollmgr loop is started, so no locking.
 */
SOCKET
pollmgr_add_chan(int slot, struct pollmgr_handler *handler)
{
    if (slot >= POLLMGR_SLOT_FIRST_DYNAMIC) {
        handler->slot = -1;
        return -1;
    }

    pollmgr_add_at(slot, handler, pollmgr.chan[slot][POLLMGR_CHFD_RD], POLLIN);
    return pollmgr.chan[slot][POLLMGR_CHFD_WR];
}


/*
 * Must be called from pollmgr loop (via callbacks), so no locking.
 */
int
pollmgr_add(struct pollmgr_handler *handler, SOCKET fd, int events)
{
    int slot;

    DPRINTF2(("%s: new fd %d\n", __func__, fd));

    if (pollmgr.nfds == pollmgr.capacity) {
        struct pollfd *newfds;
        struct pollmgr_handler **newhdls;
        nfds_t newcap;
        nfds_t i;

        newcap = pollmgr.capacity * 2;

        newfds = (struct pollfd *)
            realloc(pollmgr.fds, newcap * sizeof(*pollmgr.fds));
        if (newfds == NULL) {
            perror("realloc");
            handler->slot = -1;
            return -1;
        }

        pollmgr.fds = newfds; /* don't crash/leak if realloc(handlers) fails */
        /* but don't update capacity yet! */

        newhdls = (struct pollmgr_handler **)
            realloc(pollmgr.handlers, newcap * sizeof(*pollmgr.handlers));
        if (newhdls == NULL) {
            perror("realloc");
            /* if we failed to realloc here, then fds points to the
             * new array, but we pretend we still has old capacity */
            handler->slot = -1;
            return -1;
        }

        pollmgr.handlers = newhdls;
        pollmgr.capacity = newcap;

        for (i = pollmgr.nfds; i < newcap; ++i) {
            newfds[i].fd = INVALID_SOCKET;
            newfds[i].events = 0;
            newfds[i].revents = 0;
            newhdls[i] = NULL;
        }
    }

    slot = pollmgr.nfds;
    ++pollmgr.nfds;

    pollmgr_add_at(slot, handler, fd, events);
    return slot;
}


static void
pollmgr_add_at(int slot, struct pollmgr_handler *handler, SOCKET fd, int events)
{
    pollmgr.fds[slot].fd = fd;
    pollmgr.fds[slot].events = events;
    pollmgr.fds[slot].revents = 0;
    pollmgr.handlers[slot] = handler;

    handler->slot = slot;
}


ssize_t
pollmgr_chan_send(int slot, void *buf, size_t nbytes)
{
    SOCKET fd;
    ssize_t nsent;

    if (slot >= POLLMGR_SLOT_FIRST_DYNAMIC) {
        return -1;
    }

    fd = pollmgr.chan[slot][POLLMGR_CHFD_WR];
    nsent = send(fd, buf, (int)nbytes, 0);
    if (nsent == SOCKET_ERROR) {
        warn("send on chan %d", slot);
        return -1;
    }
    else if ((size_t)nsent != nbytes) {
        warnx("send on chan %d: datagram truncated to %u bytes",
              slot, (unsigned int)nsent);
        return -1;
    }

    return nsent;
}


/**
 * Receive a pointer sent over poll manager channel.
 */
void *
pollmgr_chan_recv_ptr(struct pollmgr_handler *handler, SOCKET fd, int revents)
{
    void *ptr;
    ssize_t nread;

    if (revents & POLLNVAL) {
        errx(EXIT_FAILURE, "chan %d: fd invalid", (int)handler->slot);
        /* NOTREACHED */
    }

    if (revents & (POLLERR | POLLHUP)) {
        errx(EXIT_FAILURE, "chan %d: fd error", (int)handler->slot);
        /* NOTREACHED */
    }

    LWIP_ASSERT1(revents & POLLIN);
    nread = recv(fd, (char *)&ptr, sizeof(ptr), 0);

    if (nread == SOCKET_ERROR) {
        err(EXIT_FAILURE, "chan %d: recv", (int)handler->slot);
        /* NOTREACHED */
    }
    if (nread != sizeof(ptr)) {
        errx(EXIT_FAILURE, "chan %d: recv: read %d bytes",
             (int)handler->slot, (int)nread);
        /* NOTREACHED */
    }

    return ptr;
}


void
pollmgr_update_events(int slot, int events)
{
    LWIP_ASSERT1(slot >= POLLMGR_SLOT_FIRST_DYNAMIC);
    LWIP_ASSERT1((nfds_t)slot < pollmgr.nfds);

    pollmgr.fds[slot].events = events;
}


void
pollmgr_del_slot(int slot)
{
    LWIP_ASSERT1(slot >= POLLMGR_SLOT_FIRST_DYNAMIC);

    DPRINTF2(("%s(%d): fd %d ! DELETED\n",
              __func__, slot, pollmgr.fds[slot].fd));

    pollmgr.fds[slot].fd = INVALID_SOCKET; /* see poll loop */
}


void
pollmgr_thread(void *ignored)
{
    LWIP_UNUSED_ARG(ignored);
    pollmgr_loop();
}


static void
pollmgr_loop(void)
{
    int nready;
    SOCKET delfirst;
    SOCKET *pdelprev;
    int i;

    for (;;) {
#ifndef RT_OS_WINDOWS
        nready = poll(pollmgr.fds, pollmgr.nfds, -1);
#else
        int rc = RTWinPoll(pollmgr.fds, pollmgr.nfds,RT_INDEFINITE_WAIT, &nready);
        if (RT_FAILURE(rc)) {
            err(EXIT_FAILURE, "poll"); /* XXX: what to do on error? */
            /* NOTREACHED*/
        }
#endif

        DPRINTF2(("%s: ready %d fd%s\n",
                  __func__, nready, (nready == 1 ? "" : "s")));

        if (nready < 0) {
            if (errno == EINTR) {
                continue;
            }

            err(EXIT_FAILURE, "poll"); /* XXX: what to do on error? */
            /* NOTREACHED*/
        }
        else if (nready == 0) { /* cannot happen, we wait forever (-1) */
            continue;           /* - but be defensive */
        }


        delfirst = INVALID_SOCKET;
        pdelprev = &delfirst;

        for (i = 0; (nfds_t)i < pollmgr.nfds && nready > 0; ++i) {
            struct pollmgr_handler *handler;
            SOCKET fd;
            int revents, nevents;

            fd = pollmgr.fds[i].fd;
            revents = pollmgr.fds[i].revents;

            /*
             * Channel handlers can request deletion of dynamic slots
             * by calling pollmgr_del_slot() that clobbers slot's fd.
             */
            if (fd == INVALID_SOCKET && i >= POLLMGR_SLOT_FIRST_DYNAMIC) {
                /* adjust count if events were pending for that slot */
                if (revents != 0) {
                    --nready;
                }

                /* pretend that slot handler requested deletion */
                nevents = -1;
                goto update_events;
            }

            if (revents == 0) {
                continue; /* next fd */
            }
            --nready;

            handler = pollmgr.handlers[i];

            if (handler != NULL && handler->callback != NULL) {
#if LWIP_PROXY_DEBUG /* DEBUG */
                if (i < POLLMGR_SLOT_FIRST_DYNAMIC) {
                    if (revents == POLLIN) {
                        DPRINTF2(("%s: ch %d\n", __func__, i));
                    }
                    else {
                        DPRINTF2(("%s: ch %d @ revents 0x%x!\n",
                                  __func__, i, revents));
                    }
                }
                else {
                    DPRINTF2(("%s: fd %d @ revents 0x%x\n",
                              __func__, fd, revents));
                }
#endif /* DEBUG */
                nevents = (*handler->callback)(handler, fd, revents);
            }
            else {
                DPRINTF0(("%s: invalid handler for fd %d: ", __func__, fd));
                if (handler == NULL) {
                    DPRINTF0(("NULL\n"));
                }
                else {
                    DPRINTF0(("%p (callback = NULL)\n", (void *)handler));
                }
                nevents = -1;   /* delete it */
            }

          update_events:
            if (nevents >= 0) {
                if (nevents != pollmgr.fds[i].events) {
                    DPRINTF2(("%s: fd %d ! nevents 0x%x\n",
                              __func__, fd, nevents));
                }
                pollmgr.fds[i].events = nevents;
            }
            else if (i < POLLMGR_SLOT_FIRST_DYNAMIC) {
                /* Don't garbage-collect channels. */
                DPRINTF2(("%s: fd %d ! DELETED (channel %d)\n",
                          __func__, fd, i));
                pollmgr.fds[i].fd = INVALID_SOCKET;
                pollmgr.fds[i].events = 0;
                pollmgr.fds[i].revents = 0;
                pollmgr.handlers[i] = NULL;
            }
            else {
                DPRINTF2(("%s: fd %d ! DELETED\n", __func__, fd));

                /* schedule for deletion (see g/c loop for details) */
                *pdelprev = i;  /* make previous entry point to us */
                pdelprev = &pollmgr.fds[i].fd;

                pollmgr.fds[i].fd = INVALID_SOCKET; /* end of list (for now) */
                pollmgr.fds[i].events = POLLMGR_GARBAGE;
                pollmgr.fds[i].revents = 0;
                pollmgr.handlers[i] = NULL;
            }
        } /* processing loop */


        /*
         * Garbage collect and compact the array.
         *
         * We overload pollfd::fd of garbage entries to store the
         * index of the next garbage entry.  The garbage list is
         * co-directional with the fds array.  The index of the first
         * entry is in "delfirst", the last entry "points to"
         * INVALID_SOCKET.
         *
         * See update_events code for nevents < 0 at the end of the
         * processing loop above.
         */
        while (delfirst != INVALID_SOCKET) {
            const int last = pollmgr.nfds - 1;

            /*
             * We want a live entry in the last slot to swap into the
             * freed slot, so make sure we have one.
             */
            if (pollmgr.fds[last].events == POLLMGR_GARBAGE /* garbage */
                || pollmgr.fds[last].fd == INVALID_SOCKET)  /* or killed */
            {
                /* drop garbage entry at the end of the array */
                --pollmgr.nfds;

                if (delfirst == last) {
                    /* congruent to delnext >= pollmgr.nfds test below */
                    delfirst = INVALID_SOCKET; /* done */
                }
            }
            else {
                const SOCKET delnext = pollmgr.fds[delfirst].fd;

                /* copy live entry at the end to the first slot being freed */
                pollmgr.fds[delfirst] = pollmgr.fds[last]; /* struct copy */
                pollmgr.handlers[delfirst] = pollmgr.handlers[last];
                pollmgr.handlers[delfirst]->slot = (int)delfirst;
                --pollmgr.nfds;

                if ((nfds_t)delnext >= pollmgr.nfds) {
                    delfirst = INVALID_SOCKET; /* done */
                }
                else {
                    delfirst = delnext;
                }
            }

            pollmgr.fds[last].fd = INVALID_SOCKET;
            pollmgr.fds[last].events = 0;
            pollmgr.fds[last].revents = 0;
            pollmgr.handlers[last] = NULL;
        }
    } /* poll loop */
}


/**
 * Create strongly held refptr.
 */
struct pollmgr_refptr *
pollmgr_refptr_create(struct pollmgr_handler *ptr)
{
    struct pollmgr_refptr *rp;

    LWIP_ASSERT1(ptr != NULL);

    rp = (struct pollmgr_refptr *)malloc(sizeof (*rp));
    if (rp == NULL) {
        return NULL;
    }

    sys_mutex_new(&rp->lock);
    rp->ptr = ptr;
    rp->strong = 1;
    rp->weak = 0;

    return rp;
}


static void
pollmgr_refptr_delete(struct pollmgr_refptr *rp)
{
    if (rp == NULL) {
        return;
    }

    LWIP_ASSERT1(rp->strong == 0);
    LWIP_ASSERT1(rp->weak == 0);

    sys_mutex_free(&rp->lock);
    free(rp);
}


/**
 * Add weak reference before "rp" is sent over a poll manager channel.
 */
void
pollmgr_refptr_weak_ref(struct pollmgr_refptr *rp)
{
    sys_mutex_lock(&rp->lock);

    LWIP_ASSERT1(rp->ptr != NULL);
    LWIP_ASSERT1(rp->strong > 0);

    ++rp->weak;

    sys_mutex_unlock(&rp->lock);
}


/**
 * Try to get the pointer from implicitely weak reference we've got
 * from a channel.
 *
 * If we detect that the object is still strongly referenced, but no
 * longer registered with the poll manager we abort strengthening
 * conversion here b/c lwip thread callback is already scheduled to
 * destruct the object.
 */
struct pollmgr_handler *
pollmgr_refptr_get(struct pollmgr_refptr *rp)
{
    struct pollmgr_handler *handler;
    size_t weak;

    sys_mutex_lock(&rp->lock);

    LWIP_ASSERT1(rp->weak > 0);
    weak = --rp->weak;

    handler = rp->ptr;
    if (handler == NULL) {
        LWIP_ASSERT1(rp->strong == 0);
        sys_mutex_unlock(&rp->lock);
        if (weak == 0) {
            pollmgr_refptr_delete(rp);
        }
        return NULL;
    }

    LWIP_ASSERT1(rp->strong == 1);

    /*
     * Here we woild do:
     *
     *   ++rp->strong;
     *
     * and then, after channel handler is done, we would decrement it
     * back.
     *
     * Instead we check that the object is still registered with poll
     * manager. If it is, there's no race with lwip thread trying to
     * drop its strong reference, as lwip thread callback to destruct
     * the object is always scheduled by its poll manager callback.
     *
     * Conversly, if we detect that the object is no longer registered
     * with poll manager, we immediately abort. Since channel handler
     * can't do anything useful anyway and would have to return
     * immediately.
     *
     * Since channel handler would always find rp->strong as it had
     * left it, just elide extra strong reference creation to avoid
     * the whole back-and-forth.
     */

    if (handler->slot < 0) { /* no longer polling */
        sys_mutex_unlock(&rp->lock);
        return NULL;
    }

    sys_mutex_unlock(&rp->lock);
    return handler;
}


/**
 * Remove (the only) strong reference.
 *
 * If it were real strong/weak pointers, we should also call
 * destructor for the referenced object, but
 */
void
pollmgr_refptr_unref(struct pollmgr_refptr *rp)
{
    sys_mutex_lock(&rp->lock);

    LWIP_ASSERT1(rp->strong == 1);
    --rp->strong;

    if (rp->strong > 0) {
        sys_mutex_unlock(&rp->lock);
    }
    else {
        size_t weak;

        /* void *ptr = rp->ptr; */
        rp->ptr = NULL;

        /* delete ptr; // see doc comment */

        weak = rp->weak;
        sys_mutex_unlock(&rp->lock);
        if (weak == 0) {
            pollmgr_refptr_delete(rp);
        }
    }
}