Archipelago » qemu

/*

 * Inter-VM Shared Memory PCI device.

 *

 * Author:

 *      Cam Macdonell <cam@cs.ualberta.ca>

 *

 * Based On: cirrus_vga.c

 *          Copyright (c) 2004 Fabrice Bellard

 *          Copyright (c) 2004 Makoto Suzuki (suzu)

 *

 *      and rtl8139.c

 *          Copyright (c) 2006 Igor Kovalenko

 *

 * This code is licensed under the GNU GPL v2.

 */

#include "hw.h"

#include "pc.h"

#include "pci.h"

#include "msix.h"

#include "kvm.h"

#include <sys/mman.h>

#include <sys/types.h>

#define IVSHMEM_IOEVENTFD   0

#define IVSHMEM_MSI     1

#define IVSHMEM_PEER    0

#define IVSHMEM_MASTER  1

#define IVSHMEM_REG_BAR_SIZE 0x100

//#define DEBUG_IVSHMEM

#ifdef DEBUG_IVSHMEM

#define IVSHMEM_DPRINTF(fmt, ...)        \

    do {printf("IVSHMEM: " fmt, ## __VA_ARGS__); } while (0)

#else

#define IVSHMEM_DPRINTF(fmt, ...)

#endif

typedef struct Peer {

    int nb_eventfds;

    int *eventfds;

} Peer;

typedef struct EventfdEntry {

    PCIDevice *pdev;

    int vector;

} EventfdEntry;

typedef struct IVShmemState {

    PCIDevice dev;

    uint32_t intrmask;

    uint32_t intrstatus;

    uint32_t doorbell;

    CharDriverState **eventfd_chr;

    CharDriverState *server_chr;

    MemoryRegion ivshmem_mmio;

    pcibus_t mmio_addr;

    /* We might need to register the BAR before we actually have the memory.

     * So prepare a container MemoryRegion for the BAR immediately and

     * add a subregion when we have the memory.

     */

    MemoryRegion bar;

    MemoryRegion ivshmem;

    MemoryRegion msix_bar;

    uint64_t ivshmem_size; /* size of shared memory region */

    int shm_fd; /* shared memory file descriptor */

    Peer *peers;

    int nb_peers; /* how many guests we have space for */

    int max_peer; /* maximum numbered peer */

    int vm_id;

    uint32_t vectors;

    uint32_t features;

    EventfdEntry *eventfd_table;

    char * shmobj;

    char * sizearg;

    char * role;

    int role_val;   /* scalar to avoid multiple string comparisons */

} 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,

                                                    unsigned int feature) {

    return (ivs->features & (1 << feature));

}

static inline bool is_power_of_two(uint64_t x) {

    return (x & (x - 1)) == 0;

}

/* 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_write(void *opaque, target_phys_addr_t addr,

                             uint64_t val, unsigned size)

{

    IVShmemState *s = opaque;

    uint64_t write_one = 1;

    uint16_t dest = val >> 16;

    uint16_t vector = val & 0xff;

    addr &= 0xfc;

    IVSHMEM_DPRINTF("writing to addr " TARGET_FMT_plx "\n", addr);

    switch (addr)

    {

        case INTRMASK:

            ivshmem_IntrMask_write(s, val);

            break;

        case INTRSTATUS:

            ivshmem_IntrStatus_write(s, val);

            break;

        case DOORBELL:

            /* check that dest VM ID is reasonable */

            if (dest > s->max_peer) {

                IVSHMEM_DPRINTF("Invalid destination VM ID (%d)\n", dest);

                break;

            }

            /* check doorbell range */

            if (vector < s->peers[dest].nb_eventfds) {

                IVSHMEM_DPRINTF("Writing %" PRId64 " to VM %d on vector %d\n",

                                                    write_one, dest, vector);

                if (write(s->peers[dest].eventfds[vector],

                                                    &(write_one), 8) != 8) {

                    IVSHMEM_DPRINTF("error writing to eventfd\n");

                }

            }

            break;

        default:

            IVSHMEM_DPRINTF("Invalid VM Doorbell VM %d\n", dest);

    }

}

static uint64_t ivshmem_io_read(void *opaque, target_phys_addr_t addr,

                                unsigned size)

{

    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 VM ID if the memory is mapped */

            if (s->shm_fd > 0) {

                ret = s->vm_id;

            } else {

                ret = -1;

            }

            break;

        default:

            IVSHMEM_DPRINTF("why are we reading " TARGET_FMT_plx "\n", addr);

            ret = 0;

    }

    return ret;

}

static const MemoryRegionOps ivshmem_mmio_ops = {

    .read = ivshmem_io_read,

    .write = ivshmem_io_write,

    .endianness = DEVICE_NATIVE_ENDIAN,

    .impl = {

        .min_access_size = 4,

        .max_access_size = 4,

    },

};

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("interrupt on vector %p %d\n", pdev, 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) {

        fprintf(stderr, "creating eventfd for eventfd %d failed\n", eventfd);

        exit(-1);

    }

    /* if MSI is supported we need multiple interrupts */

    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 fd) {

    /* check that the guest isn't going to try and map more memory than the

     * the object has allocated return -1 to indicate error */

    struct stat buf;

    fstat(fd, &buf);

    if (s->ivshmem_size > buf.st_size) {

        fprintf(stderr,

                "IVSHMEM ERROR: Requested memory size greater"

                " than shared object size (%" PRIu64 " > %" PRIu64")\n",

                s->ivshmem_size, (uint64_t)buf.st_size);

        return -1;

    } else {

        return 0;

    }

}

/* create the shared memory BAR when we are not using the server, so we can

 * create the BAR and map the memory immediately */

static void create_shared_memory_BAR(IVShmemState *s, int fd) {

    void * ptr;

    s->shm_fd = fd;

    ptr = mmap(0, s->ivshmem_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

    memory_region_init_ram_ptr(&s->ivshmem, &s->dev.qdev, "ivshmem.bar2",

                               s->ivshmem_size, ptr);

    memory_region_add_subregion(&s->bar, 0, &s->ivshmem);

    /* region for shared memory */

    pci_register_bar(&s->dev, 2, PCI_BASE_ADDRESS_SPACE_MEMORY, &s->bar);

}

static void close_guest_eventfds(IVShmemState *s, int posn)

{

    int i, guest_curr_max;

    guest_curr_max = s->peers[posn].nb_eventfds;

    for (i = 0; i < guest_curr_max; i++) {

        kvm_set_ioeventfd_mmio_long(s->peers[posn].eventfds[i],

                    s->mmio_addr + DOORBELL, (posn << 16) | i, 0);

        close(s->peers[posn].eventfds[i]);

    }

    g_free(s->peers[posn].eventfds);

    s->peers[posn].nb_eventfds = 0;

}

static void setup_ioeventfds(IVShmemState *s) {

    int i, j;

    for (i = 0; i <= s->max_peer; i++) {

        for (j = 0; j < s->peers[i].nb_eventfds; j++) {

            memory_region_add_eventfd(&s->ivshmem_mmio,

                                      DOORBELL,

                                      4,

                                      true,

                                      (i << 16) | j,

                                      s->peers[i].eventfds[j]);

        }

    }

}

/* 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_nb_alloc;

    old_nb_alloc = s->nb_peers;

    while (new_min_size >= s->nb_peers)

        s->nb_peers = s->nb_peers * 2;

    IVSHMEM_DPRINTF("bumping storage to %d guests\n", s->nb_peers);

    s->peers = g_realloc(s->peers, s->nb_peers * sizeof(Peer));

    /* zero out new pointers */

    for (j = old_nb_alloc; j < s->nb_peers; j++) {

        s->peers[j].eventfds = NULL;

        s->peers[j].nb_eventfds = 0;

    }

}

static void ivshmem_read(void *opaque, const uint8_t * buf, int flags)

{

    IVShmemState *s = opaque;

    int incoming_fd, tmp_fd;

    int guest_max_eventfd;

    long incoming_posn;

    memcpy(&incoming_posn, buf, sizeof(long));

    /* pick off s->server_chr->msgfd and store it, posn should accompany msg */

    tmp_fd = qemu_chr_get_msgfd(s->server_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->nb_peers) {

        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->peers[incoming_posn].eventfds == 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 (incoming_fd == -1) {

        fprintf(stderr, "could not allocate file descriptor %s\n",

                                                            strerror(errno));

        return;

    }

    /* if the position is -1, then it's shared memory region fd */

    if (incoming_posn == -1) {

        void * map_ptr;

        s->max_peer = 0;

        if (check_shm_size(s, incoming_fd) == -1) {

            exit(-1);

        }

        /* mmap the region and map into the BAR2 */

        map_ptr = mmap(0, s->ivshmem_size, PROT_READ|PROT_WRITE, MAP_SHARED,

                                                            incoming_fd, 0);

        memory_region_init_ram_ptr(&s->ivshmem, &s->dev.qdev,

                                   "ivshmem.bar2", s->ivshmem_size, map_ptr);

        IVSHMEM_DPRINTF("guest h/w addr = %" PRIu64 ", size = %" PRIu64 "\n",

                         s->ivshmem_offset, s->ivshmem_size);

        memory_region_add_subregion(&s->bar, 0, &s->ivshmem);

        /* only store the fd if it is successfully mapped */

        s->shm_fd = incoming_fd;

        return;

    }

    /* each guest has an array of eventfds, and we keep track of how many

     * guests for each VM */

    guest_max_eventfd = s->peers[incoming_posn].nb_eventfds;

    if (guest_max_eventfd == 0) {

        /* one eventfd per MSI vector */

        s->peers[incoming_posn].eventfds = (int *) g_malloc(s->vectors *

                                                                sizeof(int));

    }

    /* this is an eventfd for a particular guest VM */

    IVSHMEM_DPRINTF("eventfds[%ld][%d] = %d\n", incoming_posn,

                                            guest_max_eventfd, incoming_fd);

    s->peers[incoming_posn].eventfds[guest_max_eventfd] = incoming_fd;

    /* increment count for particular guest */

    s->peers[incoming_posn].nb_eventfds++;

    /* keep track of the maximum VM ID */

    if (incoming_posn > s->max_peer) {

        s->max_peer = incoming_posn;

    }

    if (incoming_posn == s->vm_id) {

        s->eventfd_chr[guest_max_eventfd] = create_eventfd_chr_device(s,

                   s->peers[s->vm_id].eventfds[guest_max_eventfd],

                   guest_max_eventfd);

    }

    if (ivshmem_has_feature(s, IVSHMEM_IOEVENTFD)) {

        if (kvm_set_ioeventfd_mmio_long(incoming_fd, s->mmio_addr + DOORBELL,

                        (incoming_posn << 16) | guest_max_eventfd, 1) < 0) {

            fprintf(stderr, "ivshmem: ioeventfd not available\n");

        }

    }

    return;

}

static void ivshmem_reset(DeviceState *d)

{

    IVShmemState *s = DO_UPCAST(IVShmemState, dev.qdev, d);

    s->intrstatus = 0;

    return;

}

static uint64_t ivshmem_get_size(IVShmemState * s) {

    uint64_t value;

    char *ptr;

    value = strtoull(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 void ivshmem_setup_msi(IVShmemState * s) {

    int i;

    /* allocate the MSI-X vectors */

    memory_region_init(&s->msix_bar, "ivshmem-msix", 4096);

    if (!msix_init(&s->dev, s->vectors, &s->msix_bar, 1, 0)) {

        pci_register_bar(&s->dev, 1, PCI_BASE_ADDRESS_SPACE_MEMORY,

                         &s->msix_bar);

        IVSHMEM_DPRINTF("msix initialized (%d vectors)\n", s->vectors);

    } else {

        IVSHMEM_DPRINTF("msix initialization failed\n");

        exit(1);

    }

    /* 'activate' the vectors */

    for (i = 0; i < s->vectors; i++) {

        msix_vector_use(&s->dev, i);

    }

    /* allocate Qemu char devices for receiving interrupts */

    s->eventfd_table = g_malloc0(s->vectors * sizeof(EventfdEntry));

}

static void ivshmem_save(QEMUFile* f, void *opaque)

{

    IVShmemState *proxy = opaque;

    IVSHMEM_DPRINTF("ivshmem_save\n");

    pci_device_save(&proxy->dev, f);

    if (ivshmem_has_feature(proxy, IVSHMEM_MSI)) {

        msix_save(&proxy->dev, f);

    } else {

        qemu_put_be32(f, proxy->intrstatus);

        qemu_put_be32(f, proxy->intrmask);

    }

}

static int ivshmem_load(QEMUFile* f, void *opaque, int version_id)

{

    IVSHMEM_DPRINTF("ivshmem_load\n");

    IVShmemState *proxy = opaque;

    int ret, i;

    if (version_id > 0) {

        return -EINVAL;

    }

    if (proxy->role_val == IVSHMEM_PEER) {

        fprintf(stderr, "ivshmem: 'peer' devices are not migratable\n");

        return -EINVAL;

    }

    ret = pci_device_load(&proxy->dev, f);

    if (ret) {

        return ret;

    }

    if (ivshmem_has_feature(proxy, IVSHMEM_MSI)) {

        msix_load(&proxy->dev, f);

        for (i = 0; i < proxy->vectors; i++) {

            msix_vector_use(&proxy->dev, i);

        }

    } else {

        proxy->intrstatus = qemu_get_be32(f);

        proxy->intrmask = qemu_get_be32(f);

    }

    return 0;

}

static int pci_ivshmem_init(PCIDevice *dev)

{

    IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);

    uint8_t *pci_conf;

    if (s->sizearg == NULL)

        s->ivshmem_size = 4 << 20; /* 4 MB default */

    else {

        s->ivshmem_size = ivshmem_get_size(s);

    }

    register_savevm(&s->dev.qdev, "ivshmem", 0, 0, ivshmem_save, ivshmem_load,

                                                                        dev);

    /* IRQFD requires MSI */

    if (ivshmem_has_feature(s, IVSHMEM_IOEVENTFD) &&

        !ivshmem_has_feature(s, IVSHMEM_MSI)) {

        fprintf(stderr, "ivshmem: ioeventfd/irqfd requires MSI\n");

        exit(1);

    }

    /* check that role is reasonable */

    if (s->role) {

        if (strncmp(s->role, "peer", 5) == 0) {

            s->role_val = IVSHMEM_PEER;

        } else if (strncmp(s->role, "master", 7) == 0) {

            s->role_val = IVSHMEM_MASTER;

        } else {

            fprintf(stderr, "ivshmem: 'role' must be 'peer' or 'master'\n");

            exit(1);

        }

    } else {

        s->role_val = IVSHMEM_MASTER; /* default */

    }

    if (s->role_val == IVSHMEM_PEER) {

        register_device_unmigratable(&s->dev.qdev, "ivshmem", s);

    }

    pci_conf = s->dev.config;

    pci_conf[PCI_COMMAND] = PCI_COMMAND_IO | PCI_COMMAND_MEMORY;

    pci_config_set_interrupt_pin(pci_conf, 1);

    s->shm_fd = 0;

    memory_region_init_io(&s->ivshmem_mmio, &ivshmem_mmio_ops, s,

                          "ivshmem-mmio", IVSHMEM_REG_BAR_SIZE);

    if (ivshmem_has_feature(s, IVSHMEM_IOEVENTFD)) {

        setup_ioeventfds(s);

    }

    /* region for registers*/

    pci_register_bar(&s->dev, 0, PCI_BASE_ADDRESS_SPACE_MEMORY,

                     &s->ivshmem_mmio);

    memory_region_init(&s->bar, "ivshmem-bar2-container", s->ivshmem_size);

    if ((s->server_chr != NULL) &&

                        (strncmp(s->server_chr->filename, "unix:", 5) == 0)) {

        /* if we get a UNIX socket as the parameter we will talk

         * to the ivshmem server to receive the memory region */

        if (s->shmobj != NULL) {

            fprintf(stderr, "WARNING: do not specify both 'chardev' "

                                                "and 'shm' with ivshmem\n");

        }

        IVSHMEM_DPRINTF("using shared memory server (socket = %s)\n",

                                                    s->server_chr->filename);

        if (ivshmem_has_feature(s, IVSHMEM_MSI)) {

            ivshmem_setup_msi(s);

        }

        /* we allocate enough space for 16 guests and grow as needed */

        s->nb_peers = 16;

        s->vm_id = -1;

        /* allocate/initialize space for interrupt handling */

        s->peers = g_malloc0(s->nb_peers * sizeof(Peer));

        pci_register_bar(&s->dev, 2,

                         PCI_BASE_ADDRESS_SPACE_MEMORY, &s->ivshmem);

        s->eventfd_chr = g_malloc0(s->vectors * sizeof(CharDriverState *));

        qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive, ivshmem_read,

                     ivshmem_event, s);

    } 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, "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, "ivshmem: could not open shared file\n");

            exit(-1);

        }

        if (check_shm_size(s, fd) == -1) {

            exit(-1);

        }

        create_shared_memory_BAR(s, fd);

    }

    return 0;

}

static int pci_ivshmem_uninit(PCIDevice *dev)

{

    IVShmemState *s = DO_UPCAST(IVShmemState, dev, dev);

    memory_region_destroy(&s->ivshmem_mmio);

    memory_region_del_subregion(&s->bar, &s->ivshmem);

    memory_region_destroy(&s->ivshmem);

    memory_region_destroy(&s->bar);

    unregister_savevm(&dev->qdev, "ivshmem", s);

    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,

    .vendor_id  = PCI_VENDOR_ID_REDHAT_QUMRANET,

    .device_id  = 0x1110,

    .class_id   = PCI_CLASS_MEMORY_RAM,

    .qdev.props = (Property[]) {

        DEFINE_PROP_CHR("chardev", IVShmemState, server_chr),

        DEFINE_PROP_STRING("size", IVShmemState, sizearg),

        DEFINE_PROP_UINT32("vectors", IVShmemState, vectors, 1),

        DEFINE_PROP_BIT("ioeventfd", IVShmemState, features, IVSHMEM_IOEVENTFD, false),

        DEFINE_PROP_BIT("msi", IVShmemState, features, IVSHMEM_MSI, true),

        DEFINE_PROP_STRING("shm", IVShmemState, shmobj),

        DEFINE_PROP_STRING("role", IVShmemState, role),

        DEFINE_PROP_END_OF_LIST(),

    }

};

static void ivshmem_register_devices(void)

{

    pci_qdev_register(&ivshmem_info);

}

device_init(ivshmem_register_devices)