Re: [PATCH v5 4/5] Inter-VM shared memory PCI device

[Anthony Liguori <anthony@codemonkey.ws>]

On 04/21/2010 12:53 PM, Cam Macdonell wrote:
> Support an inter-vm shared memory device that maps a shared-memory object as a
> PCI device in the guest.  This patch also supports interrupts between guest by
> communicating over a unix domain socket.  This patch applies to the qemu-kvm
> repository.
>
>      -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
>
> Interrupts are supported between multiple VMs by using a shared memory server
> by using a chardev socket.
>
>      -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
>                      [,chardev=<id>][,msi=on][,irqfd=on][,vectors=n]
>      -chardev socket,path=<path>,id=<id>
>
> (shared memory server is qemu.git/contrib/ivshmem-server)
>
> Sample programs and init scripts are in a git repo here:
>
>      www.gitorious.org/nahanni
> ---
>   Makefile.target |    3 +
>   hw/ivshmem.c    |  727 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   qemu-char.c     |    6 +
>   qemu-char.h     |    3 +
>   qemu-doc.texi   |   25 ++
>   5 files changed, 764 insertions(+), 0 deletions(-)
>   create mode 100644 hw/ivshmem.c
>
> diff --git a/Makefile.target b/Makefile.target
> index 1ffd802..bc9a681 100644
> --- a/Makefile.target
> +++ b/Makefile.target
> @@ -199,6 +199,9 @@ obj-$(CONFIG_USB_OHCI) += usb-ohci.o
>   obj-y += rtl8139.o
>   obj-y += e1000.o
>
> +# Inter-VM PCI shared memory
> +obj-y += ivshmem.o
> +
>   # Hardware support
>   obj-i386-y = pckbd.o dma.o
>   obj-i386-y += vga.o
> diff --git a/hw/ivshmem.c b/hw/ivshmem.c
> new file mode 100644
> index 0000000..f8d8fdb
> --- /dev/null
> +++ b/hw/ivshmem.c
> @@ -0,0 +1,727 @@
> +/*
> + * Inter-VM Shared Memory PCI device.
> + *
> + * Author:
> + *      Cam Macdonell<cam@cs.ualberta.ca>
> + *
> + * Based On: cirrus_vga.c and rtl8139.c
> + *
> + * This code is licensed under the GNU GPL v2.
> + */
> +#include<sys/mman.h>
> +#include<sys/types.h>
> +#include<sys/socket.h>
> +#include<sys/io.h>
> +#include<sys/ioctl.h>
> +#include<sys/eventfd.h>
>    

This will break the Windows along with any non-Linux unix or any Linux 
old enough to not have eventfd support.

If it's based on cirrus_vga.c and rtl8139.c, then it ought to carry the 
respective copyrights, no?

Regards,

Anthony Liguori

> +#include "hw.h"
> +#include "console.h"
> +#include "pc.h"
> +#include "pci.h"
> +#include "sysemu.h"
> +
> +#include "msix.h"
> +#include "qemu-kvm.h"
> +#include "libkvm.h"
> +
> +#include<sys/eventfd.h>
> +#include<sys/mman.h>
> +#include<sys/socket.h>
> +#include<sys/ioctl.h>
> +
> +#define IVSHMEM_IRQFD   0
> +#define IVSHMEM_MSI     1
> +
> +#define DEBUG_IVSHMEM
> +#ifdef DEBUG_IVSHMEM
> +#define IVSHMEM_DPRINTF(fmt, args...)        \
> +    do {printf("IVSHMEM: " fmt, ##args); } while (0)
> +#else
> +#define IVSHMEM_DPRINTF(fmt, args...)
> +#endif
> +
> +typedef struct EventfdEntry {
> +    PCIDevice *pdev;
> +    int vector;
> +} EventfdEntry;
> +
> +typedef struct IVShmemState {
> +    PCIDevice dev;
> +    uint32_t intrmask;
> +    uint32_t intrstatus;
> +    uint32_t doorbell;
> +
> +    CharDriverState * chr;
> +    CharDriverState ** eventfd_chr;
> +    int ivshmem_mmio_io_addr;
> +
> +    pcibus_t mmio_addr;
> +    unsigned long ivshmem_offset;
> +    uint64_t ivshmem_size; /* size of shared memory region */
> +    int shm_fd; /* shared memory file descriptor */
> +
> +    int nr_allocated_vms;
> +    /* array of eventfds for each guest */
> +    int ** eventfds;
> +    /* keep track of # of eventfds for each guest*/
> +    int * eventfds_posn_count;
> +
> +    int nr_alloc_guests;
> +    int vm_id;
> +    int num_eventfds;
> +    uint32_t vectors;
> +    uint32_t features;
> +    EventfdEntry *eventfd_table;
> +
> +    char * shmobj;
> +    char * sizearg;
> +} IVShmemState;
> +
> +/* registers for the Inter-VM shared memory device */
> +enum ivshmem_registers {
> +    IntrMask = 0,
> +    IntrStatus = 4,
> +    IVPosition = 8,
> +    Doorbell = 12,
> +};
> +
> +static inline uint32_t ivshmem_has_feature(IVShmemState *ivs, int feature) {
> +    return (ivs->features&  (1<<  feature));
> +}
> +
> +static inline int is_power_of_two(int x) {
> +    return (x&  (x-1)) == 0;
> +}
> +
> +static void ivshmem_map(PCIDevice *pci_dev, int region_num,
> +                    pcibus_t addr, pcibus_t size, int type)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev, pci_dev);
> +
> +    IVSHMEM_DPRINTF("addr = %u size = %u\n", (uint32_t)addr, (uint32_t)size);
> +    cpu_register_physical_memory(addr, s->ivshmem_size, s->ivshmem_offset);
> +
> +}
> +
> +/* accessing registers - based on rtl8139 */
> +static void ivshmem_update_irq(IVShmemState *s, int val)
> +{
> +    int isr;
> +    isr = (s->intrstatus&  s->intrmask)&  0xffffffff;
> +
> +    /* don't print ISR resets */
> +    if (isr) {
> +        IVSHMEM_DPRINTF("Set IRQ to %d (%04x %04x)\n",
> +           isr ? 1 : 0, s->intrstatus, s->intrmask);
> +    }
> +
> +    qemu_set_irq(s->dev.irq[0], (isr != 0));
> +}
> +
> +static void ivshmem_IntrMask_write(IVShmemState *s, uint32_t val)
> +{
> +    IVSHMEM_DPRINTF("IntrMask write(w) val = 0x%04x\n", val);
> +
> +    s->intrmask = val;
> +
> +    ivshmem_update_irq(s, val);
> +}
> +
> +static uint32_t ivshmem_IntrMask_read(IVShmemState *s)
> +{
> +    uint32_t ret = s->intrmask;
> +
> +    IVSHMEM_DPRINTF("intrmask read(w) val = 0x%04x\n", ret);
> +
> +    return ret;
> +}
> +
> +static void ivshmem_IntrStatus_write(IVShmemState *s, uint32_t val)
> +{
> +    IVSHMEM_DPRINTF("IntrStatus write(w) val = 0x%04x\n", val);
> +
> +    s->intrstatus = val;
> +
> +    ivshmem_update_irq(s, val);
> +    return;
> +}
> +
> +static uint32_t ivshmem_IntrStatus_read(IVShmemState *s)
> +{
> +    uint32_t ret = s->intrstatus;
> +
> +    /* reading ISR clears all interrupts */
> +    s->intrstatus = 0;
> +
> +    ivshmem_update_irq(s, 0);
> +
> +    return ret;
> +}
> +
> +static void ivshmem_io_writew(void *opaque, uint8_t addr, uint32_t val)
> +{
> +
> +    IVSHMEM_DPRINTF("We shouldn't be writing words\n");
> +}
> +
> +static void ivshmem_io_writel(void *opaque, uint8_t addr, uint32_t val)
> +{
> +    IVShmemState *s = opaque;
> +
> +    u_int64_t write_one = 1;
> +    u_int16_t dest = val>>  16;
> +    u_int16_t vector = val&  0xff;
> +
> +    addr&= 0xfe;
> +
> +    switch (addr)
> +    {
> +        case IntrMask:
> +            ivshmem_IntrMask_write(s, val);
> +            break;
> +
> +        case IntrStatus:
> +            ivshmem_IntrStatus_write(s, val);
> +            break;
> +
> +        case Doorbell:
> +            /* check doorbell range */
> +            if ((vector>= 0)&&  (vector<  s->eventfds_posn_count[dest])) {
> +                IVSHMEM_DPRINTF("Writing %ld to VM %d on vector %d\n", write_one, dest, vector);
> +                if (write(s->eventfds[dest][vector],&(write_one), 8) != 8) {
> +                    IVSHMEM_DPRINTF("error writing to eventfd\n");
> +                }
> +            }
> +            break;
> +        default:
> +            IVSHMEM_DPRINTF("Invalid VM Doorbell VM %d\n", dest);
> +    }
> +}
> +
> +static void ivshmem_io_writeb(void *opaque, uint8_t addr, uint32_t val)
> +{
> +    IVSHMEM_DPRINTF("We shouldn't be writing bytes\n");
> +}
> +
> +static uint32_t ivshmem_io_readw(void *opaque, uint8_t addr)
> +{
> +
> +    IVSHMEM_DPRINTF("We shouldn't be reading words\n");
> +    return 0;
> +}
> +
> +static uint32_t ivshmem_io_readl(void *opaque, uint8_t addr)
> +{
> +
> +    IVShmemState *s = opaque;
> +    uint32_t ret;
> +
> +    switch (addr)
> +    {
> +        case IntrMask:
> +            ret = ivshmem_IntrMask_read(s);
> +            break;
> +
> +        case IntrStatus:
> +            ret = ivshmem_IntrStatus_read(s);
> +            break;
> +
> +        case IVPosition:
> +            /* return my id in the ivshmem list */
> +            ret = s->vm_id;
> +            break;
> +
> +        default:
> +            IVSHMEM_DPRINTF("why are we reading 0x%x\n", addr);
> +            ret = 0;
> +    }
> +
> +    return ret;
> +
> +}
> +
> +static uint32_t ivshmem_io_readb(void *opaque, uint8_t addr)
> +{
> +    IVSHMEM_DPRINTF("We shouldn't be reading bytes\n");
> +
> +    return 0;
> +}
> +
> +static void ivshmem_mmio_writeb(void *opaque,
> +                                target_phys_addr_t addr, uint32_t val)
> +{
> +    ivshmem_io_writeb(opaque, addr&  0xFF, val);
> +}
> +
> +static void ivshmem_mmio_writew(void *opaque,
> +                                target_phys_addr_t addr, uint32_t val)
> +{
> +    ivshmem_io_writew(opaque, addr&  0xFF, val);
> +}
> +
> +static void ivshmem_mmio_writel(void *opaque,
> +                                target_phys_addr_t addr, uint32_t val)
> +{
> +    ivshmem_io_writel(opaque, addr&  0xFF, val);
> +}
> +
> +static uint32_t ivshmem_mmio_readb(void *opaque, target_phys_addr_t addr)
> +{
> +    return ivshmem_io_readb(opaque, addr&  0xFF);
> +}
> +
> +static uint32_t ivshmem_mmio_readw(void *opaque, target_phys_addr_t addr)
> +{
> +    uint32_t val = ivshmem_io_readw(opaque, addr&  0xFF);
> +    return val;
> +}
> +
> +static uint32_t ivshmem_mmio_readl(void *opaque, target_phys_addr_t addr)
> +{
> +    uint32_t val = ivshmem_io_readl(opaque, addr&  0xFF);
> +    return val;
> +}
> +
> +static CPUReadMemoryFunc *ivshmem_mmio_read[3] = {
> +    ivshmem_mmio_readb,
> +    ivshmem_mmio_readw,
> +    ivshmem_mmio_readl,
> +};
> +
> +static CPUWriteMemoryFunc *ivshmem_mmio_write[3] = {
> +    ivshmem_mmio_writeb,
> +    ivshmem_mmio_writew,
> +    ivshmem_mmio_writel,
> +};
> +
> +static void ivshmem_receive(void *opaque, const uint8_t *buf, int size)
> +{
> +    IVShmemState *s = opaque;
> +
> +    ivshmem_IntrStatus_write(s, *buf);
> +
> +    IVSHMEM_DPRINTF("ivshmem_receive 0x%02x\n", *buf);
> +}
> +
> +static int ivshmem_can_receive(void * opaque)
> +{
> +    return 8;
> +}
> +
> +static void ivshmem_event(void *opaque, int event)
> +{
> +    IVSHMEM_DPRINTF("ivshmem_event %d\n", event);
> +}
> +
> +static void fake_irqfd(void *opaque, const uint8_t *buf, int size) {
> +
> +    EventfdEntry *entry = opaque;
> +    PCIDevice *pdev = entry->pdev;
> +
> +    IVSHMEM_DPRINTF("fake irqfd on vector %d\n", entry->vector);
> +    msix_notify(pdev, entry->vector);
> +}
> +
> +static CharDriverState* create_eventfd_chr_device(void * opaque, int eventfd,
> +                                                                    int vector)
> +{
> +    /* create a event character device based on the passed eventfd */
> +    IVShmemState *s = opaque;
> +    CharDriverState * chr;
> +
> +    chr = qemu_chr_open_eventfd(eventfd);
> +
> +    if (chr == NULL) {
> +        IVSHMEM_DPRINTF("creating eventfd for eventfd %d failed\n", eventfd);
> +        exit(-1);
> +    }
> +
> +    if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
> +        s->eventfd_table[vector].pdev =&s->dev;
> +        s->eventfd_table[vector].vector = vector;
> +
> +        qemu_chr_add_handlers(chr, ivshmem_can_receive, fake_irqfd,
> +                      ivshmem_event,&s->eventfd_table[vector]);
> +    } else {
> +        qemu_chr_add_handlers(chr, ivshmem_can_receive, ivshmem_receive,
> +                      ivshmem_event, s);
> +    }
> +
> +    return chr;
> +
> +}
> +
> +static int check_shm_size(IVShmemState *s, int shmemfd) {
> +    /* check that the guest isn't going to try and map more memory than the
> +     * card server allocated return -1 to indicate error */
> +
> +    struct stat buf;
> +
> +    fstat(shmemfd,&buf);
> +
> +    if (s->ivshmem_size>  buf.st_size) {
> +        fprintf(stderr, "IVSHMEM ERROR: Requested memory size greater");
> +        fprintf(stderr, " than shared object size (%ld>  %ld)\n",
> +                                          s->ivshmem_size, buf.st_size);
> +        return -1;
> +    } else {
> +        return 0;
> +    }
> +}
> +
> +static void create_shared_memory_BAR(IVShmemState *s, int fd) {
> +
> +    s->shm_fd = fd;
> +
> +    s->ivshmem_offset = qemu_ram_mmap(s->shm_fd, s->ivshmem_size,
> +             MAP_SHARED, 0);
> +
> +    /* region for shared memory */
> +    pci_register_bar(&s->dev, 2, s->ivshmem_size,
> +                                    PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_map);
> +}
> +
> +static void close_guest_eventfds(IVShmemState *s, int posn)
> +{
> +    int i, guest_curr_max;
> +
> +    guest_curr_max = s->eventfds_posn_count[posn];
> +
> +    for (i = 0; i<  guest_curr_max; i++)
> +        close(s->eventfds[posn][i]);
> +
> +    free(s->eventfds[posn]);
> +    s->eventfds_posn_count[posn] = 0;
> +}
> +
> +/* this function increase the dynamic storage need to store data about other
> + * guests */
> +static void increase_dynamic_storage(IVShmemState *s, int new_min_size) {
> +
> +    int j, old_nr_alloc;
> +
> +    old_nr_alloc = s->nr_alloc_guests;
> +
> +    while (s->nr_alloc_guests<  new_min_size)
> +        s->nr_alloc_guests = s->nr_alloc_guests * 2;
> +
> +    IVSHMEM_DPRINTF("bumping storage to %d guests\n", s->nr_alloc_guests);
> +    s->eventfds = qemu_realloc(s->eventfds, s->nr_alloc_guests *
> +                                                        sizeof(int *));
> +    s->eventfds_posn_count = qemu_realloc(s->eventfds_posn_count,
> +                                                    s->nr_alloc_guests *
> +                                                        sizeof(int));
> +    s->eventfd_table = qemu_realloc(s->eventfd_table, s->nr_alloc_guests *
> +                                                    sizeof(EventfdEntry));
> +
> +    if ((s->eventfds == NULL) || (s->eventfds_posn_count == NULL) ||
> +            (s->eventfd_table == NULL)) {
> +        fprintf(stderr, "Allocation error - exiting\n");
> +        exit(1);
> +    }
> +
> +    if (!ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
> +        s->eventfd_chr = (CharDriverState **)qemu_realloc(s->eventfd_chr,
> +                                    s->nr_alloc_guests * sizeof(void *));
> +        if (s->eventfd_chr == NULL) {
> +            fprintf(stderr, "Allocation error - exiting\n");
> +            exit(1);
> +        }
> +    }
> +
> +    /* zero out new pointers */
> +    for (j = old_nr_alloc; j<  s->nr_alloc_guests; j++) {
> +        s->eventfds[j] = NULL;
> +    }
> +}
> +
> +static void ivshmem_read(void *opaque, const uint8_t * buf, int flags)
> +{
> +    IVShmemState *s = opaque;
> +    int incoming_fd, tmp_fd;
> +    int guest_curr_max;
> +    long incoming_posn;
> +
> +    memcpy(&incoming_posn, buf, sizeof(long));
> +    /* pick off s->chr->msgfd and store it, posn should accompany msg */
> +    tmp_fd = qemu_chr_get_msgfd(s->chr);
> +    IVSHMEM_DPRINTF("posn is %ld, fd is %d\n", incoming_posn, tmp_fd);
> +
> +    /* make sure we have enough space for this guest */
> +    if (incoming_posn>= s->nr_alloc_guests) {
> +        increase_dynamic_storage(s, incoming_posn);
> +    }
> +
> +    if (tmp_fd == -1) {
> +        /* if posn is positive and unseen before then this is our posn*/
> +        if ((incoming_posn>= 0)&&  (s->eventfds[incoming_posn] == NULL)) {
> +            /* receive our posn */
> +            s->vm_id = incoming_posn;
> +            return;
> +        } else {
> +            /* otherwise an fd == -1 means an existing guest has gone away */
> +            IVSHMEM_DPRINTF("posn %ld has gone away\n", incoming_posn);
> +            close_guest_eventfds(s, incoming_posn);
> +            return;
> +        }
> +    }
> +
> +    /* because of the implementation of get_msgfd, we need a dup */
> +    incoming_fd = dup(tmp_fd);
> +
> +    /* if the position is -1, then it's shared memory region fd */
> +    if (incoming_posn == -1) {
> +
> +        s->num_eventfds = 0;
> +
> +        if (check_shm_size(s, incoming_fd) == -1) {
> +            exit(-1);
> +        }
> +
> +        /* creating a BAR in qemu_chr callback may be crazy */
> +        create_shared_memory_BAR(s, incoming_fd);
> +
> +       return;
> +    }
> +
> +    /* each guest has an array of eventfds, and we keep track of how many
> +     * guests for each VM */
> +    guest_curr_max = s->eventfds_posn_count[incoming_posn];
> +    if (guest_curr_max == 0) {
> +        /* one eventfd per MSI vector */
> +        s->eventfds[incoming_posn] = (int *) qemu_malloc(s->vectors *
> +                                                                sizeof(int));
> +    }
> +
> +    /* this is an eventfd for a particular guest VM */
> +    IVSHMEM_DPRINTF("eventfds[%ld][%d] = %d\n", incoming_posn, guest_curr_max,
> +                                                                incoming_fd);
> +    s->eventfds[incoming_posn][guest_curr_max] = incoming_fd;
> +
> +    /* increment count for particular guest */
> +    s->eventfds_posn_count[incoming_posn]++;
> +
> +    /* ioeventfd and irqfd are enabled together,
> +     * so the flag IRQFD refers to both */
> +    if (ivshmem_has_feature(s, IVSHMEM_IRQFD)&&  guest_curr_max>= 0) {
> +        /* allocate ioeventfd for the new fd
> +         * received for guest @ incoming_posn */
> +        kvm_set_ioeventfd_mmio_long(incoming_fd, s->mmio_addr + Doorbell,
> +                                (incoming_posn<<  16) | guest_curr_max, 1);
> +    }
> +
> +    /* keep track of the maximum VM ID */
> +    if (incoming_posn>  s->num_eventfds) {
> +        s->num_eventfds = incoming_posn;
> +    }
> +
> +    if (incoming_posn == s->vm_id) {
> +        if (ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
> +            /* setup irqfd for this VM's eventfd */
> +            int vector = guest_curr_max;
> +            kvm_set_irqfd(s->eventfds[s->vm_id][guest_curr_max], vector,
> +                                        s->dev.msix_irq_entries[vector].gsi);
> +        } else {
> +            /* initialize char device for callback
> +             * if this is one of my eventfd */
> +            s->eventfd_chr[guest_curr_max] = create_eventfd_chr_device(s,
> +                s->eventfds[s->vm_id][guest_curr_max], guest_curr_max);
> +        }
> +    }
> +
> +    return;
> +}
> +
> +static void ivshmem_reset(DeviceState *d)
> +{
> +    return;
> +}
> +
> +static void ivshmem_mmio_map(PCIDevice *pci_dev, int region_num,
> +                       pcibus_t addr, pcibus_t size, int type)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev, pci_dev);
> +
> +    s->mmio_addr = addr;
> +    cpu_register_physical_memory(addr + 0, 0x400, s->ivshmem_mmio_io_addr);
> +
> +    /* now that our mmio region has been allocated, we can receive
> +     * the file descriptors */
> +    if (s->chr != NULL) {
> +        qemu_chr_add_handlers(s->chr, ivshmem_can_receive, ivshmem_read,
> +                     ivshmem_event, s);
> +    }
> +
> +}
> +
> +static uint64_t ivshmem_get_size(IVShmemState * s) {
> +
> +    uint64_t value;
> +    char *ptr;
> +
> +    value = strtoul(s->sizearg,&ptr, 10);
> +    switch (*ptr) {
> +        case 0: case 'M': case 'm':
> +            value<<= 20;
> +            break;
> +        case 'G': case 'g':
> +            value<<= 30;
> +            break;
> +        default:
> +            fprintf(stderr, "qemu: invalid ram size: %s\n", s->sizearg);
> +            exit(1);
> +    }
> +
> +    /* BARs must be a power of 2 */
> +    if (!is_power_of_two(value)) {
> +        fprintf(stderr, "ivshmem: size must be power of 2\n");
> +        exit(1);
> +    }
> +
> +    return value;
> +
> +}
> +
> +static int pci_ivshmem_init(PCIDevice *dev)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);
> +    uint8_t *pci_conf;
> +    int i;
> +
> +    if (s->sizearg == NULL)
> +        s->ivshmem_size = 4<<  20; /* 4 MB default */
> +    else {
> +        s->ivshmem_size = ivshmem_get_size(s);
> +    }
> +
> +    /* IRQFD requires MSI */
> +    if (ivshmem_has_feature(s, IVSHMEM_IRQFD)&&
> +        !ivshmem_has_feature(s, IVSHMEM_MSI)) {
> +        fprintf(stderr, "ivshmem: ioeventfd/irqfd requires MSI\n");
> +        exit(1);
> +    }
> +
> +    pci_conf = s->dev.config;
> +    pci_conf[0x00] = 0xf4; /* Qumranet vendor ID 0x5002 */
> +    pci_conf[0x01] = 0x1a;
> +    pci_conf[0x02] = 0x10;
> +    pci_conf[0x03] = 0x11;
> +    pci_conf[0x04] = PCI_COMMAND_IO | PCI_COMMAND_MEMORY;
> +    pci_conf[0x0a] = 0x00; /* RAM controller */
> +    pci_conf[0x0b] = 0x05;
> +    pci_conf[0x0e] = 0x00; /* header_type */
> +
> +    s->ivshmem_mmio_io_addr = cpu_register_io_memory(ivshmem_mmio_read,
> +                                    ivshmem_mmio_write, s);
> +    /* region for registers*/
> +    pci_register_bar(&s->dev, 0, 0x400,
> +                           PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_mmio_map);
> +
> +    /* allocate the MSI-X vectors */
> +    if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
> +
> +        if (!msix_init(&s->dev, s->vectors, 1, 0)) {
> +            pci_register_bar(&s->dev, 1,
> +                             msix_bar_size(&s->dev),
> +                             PCI_BASE_ADDRESS_SPACE_MEMORY,
> +                             msix_mmio_map);
> +            IVSHMEM_DPRINTF("msix initialized (%d vectors)\n", s->vectors);
> +        } else {
> +            IVSHMEM_DPRINTF("msix initialization failed\n");
> +        }
> +
> +        /* 'activate' the vectors */
> +        for (i = 0; i<  s->vectors; i++) {
> +            msix_vector_use(&s->dev, i);
> +        }
> +    }
> +
> +    if ((s->chr != NULL)&&  (strncmp(s->chr->filename, "unix:", 5) == 0)) {
> +        /* if we get a UNIX socket as the parameter we will talk
> +         * to the ivshmem server later once the MMIO BAR is actually
> +         * allocated (see ivshmem_mmio_map) */
> +
> +        IVSHMEM_DPRINTF("using shared memory server (socket = %s)\n",
> +                                                            s->chr->filename);
> +
> +        /* we allocate enough space for 16 guests and grow as needed */
> +        s->nr_alloc_guests = 16;
> +        s->vm_id = -1;
> +
> +        /* allocate/initialize space for interrupt handling */
> +        s->eventfds = qemu_mallocz(s->nr_alloc_guests * sizeof(int *));
> +        s->eventfd_table = qemu_mallocz(s->vectors * sizeof(EventfdEntry));
> +        s->eventfds_posn_count = qemu_mallocz(s->nr_alloc_guests * sizeof(int));
> +
> +        pci_conf[PCI_INTERRUPT_PIN] = 1; /* we are going to support interrupts */
> +
> +        if (!ivshmem_has_feature(s, IVSHMEM_IRQFD)) {
> +            s->eventfd_chr = (CharDriverState **)qemu_malloc(s->nr_alloc_guests *
> +                                                            sizeof(void *));
> +        }
> +
> +    } else {
> +        /* just map the file immediately, we're not using a server */
> +        int fd;
> +
> +        if (s->shmobj == NULL) {
> +            fprintf(stderr, "Must specify 'chardev' or 'shm' to ivshmem\n");
> +        }
> +
> +        IVSHMEM_DPRINTF("using shm_open (shm object = %s)\n", s->shmobj);
> +
> +        /* try opening with O_EXCL and if it succeeds zero the memory
> +         * by truncating to 0 */
> +        if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR|O_EXCL,
> +                        S_IRWXU|S_IRWXG|S_IRWXO))>  0) {
> +           /* truncate file to length PCI device's memory */
> +            if (ftruncate(fd, s->ivshmem_size) != 0) {
> +                fprintf(stderr, "kvm_ivshmem: could not truncate shared file\n");
> +            }
> +
> +        } else if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
> +                        S_IRWXU|S_IRWXG|S_IRWXO))<  0) {
> +            fprintf(stderr, "kvm_ivshmem: could not open shared file\n");
> +            exit(-1);
> +        }
> +
> +        create_shared_memory_BAR(s, fd);
> +
> +    }
> +
> +
> +    return 0;
> +}
> +
> +static int pci_ivshmem_uninit(PCIDevice *dev)
> +{
> +    IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);
> +
> +    cpu_unregister_io_memory(s->ivshmem_mmio_io_addr);
> +
> +    return 0;
> +}
> +
> +static PCIDeviceInfo ivshmem_info = {
> +    .qdev.name  = "ivshmem",
> +    .qdev.size  = sizeof(IVShmemState),
> +    .qdev.reset = ivshmem_reset,
> +    .init       = pci_ivshmem_init,
> +    .exit       = pci_ivshmem_uninit,
> +    .qdev.props = (Property[]) {
> +        DEFINE_PROP_CHR("chardev", IVShmemState, chr),
> +        DEFINE_PROP_STRING("size", IVShmemState, sizearg),
> +        DEFINE_PROP_UINT32("vectors", IVShmemState, vectors, 1),
> +        DEFINE_PROP_BIT("irqfd", IVShmemState, features, IVSHMEM_IRQFD, false),
> +        DEFINE_PROP_BIT("msi", IVShmemState, features, IVSHMEM_MSI, true),
> +        DEFINE_PROP_STRING("shm", IVShmemState, shmobj),
> +        DEFINE_PROP_END_OF_LIST(),
> +    }
> +};
> +
> +static void ivshmem_register_devices(void)
> +{
> +    pci_qdev_register(&ivshmem_info);
> +}
> +
> +device_init(ivshmem_register_devices)
> diff --git a/qemu-char.c b/qemu-char.c
> index 048da3f..41cb8c7 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -2076,6 +2076,12 @@ static void tcp_chr_read(void *opaque)
>       }
>   }
>
> +CharDriverState *qemu_chr_open_eventfd(int eventfd){
> +
> +    return qemu_chr_open_fd(eventfd, eventfd);
> +
> +}
> +
>   static void tcp_chr_connect(void *opaque)
>   {
>       CharDriverState *chr = opaque;
> diff --git a/qemu-char.h b/qemu-char.h
> index 3a9427b..1571091 100644
> --- a/qemu-char.h
> +++ b/qemu-char.h
> @@ -93,6 +93,9 @@ void qemu_chr_info_print(Monitor *mon, const QObject *ret_data);
>   void qemu_chr_info(Monitor *mon, QObject **ret_data);
>   CharDriverState *qemu_chr_find(const char *name);
>
> +/* add an eventfd to the qemu devices that are polled */
> +CharDriverState *qemu_chr_open_eventfd(int eventfd);
> +
>   extern int term_escape_char;
>
>   /* async I/O support */
> diff --git a/qemu-doc.texi b/qemu-doc.texi
> index 6647b7b..2df4687 100644
> --- a/qemu-doc.texi
> +++ b/qemu-doc.texi
> @@ -706,6 +706,31 @@ Using the @option{-net socket} option, it is possible to make VLANs
>   that span several QEMU instances. See @ref{sec_invocation} to have a
>   basic example.
>
> +@section Other Devices
> +
> +@subsection Inter-VM Shared Memory device
> +
> +With KVM enabled on a Linux host, a shared memory device is available.  Guests
> +map a POSIX shared memory region into the guest as a PCI device that enables
> +zero-copy communication to the application level of the guests.  The basic
> +syntax is:
> +
> +@example
> +qemu -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
> +@end example
> +
> +If desired, interrupts can be sent between guest VMs accessing the same shared
> +memory region.  Interrupt support requires using a shared memory server and
> +using a chardev socket to connect to it.  The code for the shared memory server
> +is qemu.git/contrib/ivshmem-server.  An example syntax when using the shared
> +memory server is:
> +
> +@example
> +qemu -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
> +                        [,chardev=<id>][,msi=on][,irqfd=on][,vectors=n]
> +qemu -chardev socket,path=<path>,id=<id>
> +@end example
> +
>   @node direct_linux_boot
>   @section Direct Linux Boot
>
>