block: add sheepdog driver for distributed storage support

Sheepdog is a distributed storage system for QEMU. It provides highly
available block level storage volumes to VMs like Amazon EBS.  This
patch adds a qemu block driver for Sheepdog.

Sheepdog features are:
- No node in the cluster is special (no metadata node, no control
  node, etc)
- Linear scalability in performance and capacity
- No single point of failure
- Autonomous management (zero configuration)
- Useful volume management support such as snapshot and cloning
- Thin provisioning
- Autonomous load balancing

The more details are available at the project site:
    http://www.osrg.net/sheepdog/

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 2036 insertions, 0 deletions

diff --git a/block/sheepdog.c b/block/sheepdog.c
new file mode 100644
index 0000000000..69a24940aa
--- /dev/null
+++ b/block/sheepdog.c
@@ -0,0 +1,2036 @@
+/*
+ * Copyright (C) 2009-2010 Nippon Telegraph and Telephone Corporation.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version
+ * 2 as published by the Free Software Foundation.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifdef _WIN32
+#include <windows.h>
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#else
+#include <netdb.h>
+#include <netinet/tcp.h>
+
+#define closesocket(s) close(s)
+#endif
+
+#include "qemu-common.h"
+#include "qemu-error.h"
+#include "qemu_socket.h"
+#include "block_int.h"
+
+#define SD_PROTO_VER 0x01
+
+#define SD_DEFAULT_ADDR "localhost"
+#define SD_DEFAULT_PORT "7000"
+
+#define SD_OP_CREATE_AND_WRITE_OBJ  0x01
+#define SD_OP_READ_OBJ       0x02
+#define SD_OP_WRITE_OBJ      0x03
+
+#define SD_OP_NEW_VDI        0x11
+#define SD_OP_LOCK_VDI       0x12
+#define SD_OP_RELEASE_VDI    0x13
+#define SD_OP_GET_VDI_INFO   0x14
+#define SD_OP_READ_VDIS      0x15
+
+#define SD_FLAG_CMD_WRITE    0x01
+#define SD_FLAG_CMD_COW      0x02
+
+#define SD_RES_SUCCESS       0x00 /* Success */
+#define SD_RES_UNKNOWN       0x01 /* Unknown error */
+#define SD_RES_NO_OBJ        0x02 /* No object found */
+#define SD_RES_EIO           0x03 /* I/O error */
+#define SD_RES_VDI_EXIST     0x04 /* Vdi exists already */
+#define SD_RES_INVALID_PARMS 0x05 /* Invalid parameters */
+#define SD_RES_SYSTEM_ERROR  0x06 /* System error */
+#define SD_RES_VDI_LOCKED    0x07 /* Vdi is locked */
+#define SD_RES_NO_VDI        0x08 /* No vdi found */
+#define SD_RES_NO_BASE_VDI   0x09 /* No base vdi found */
+#define SD_RES_VDI_READ      0x0A /* Cannot read requested vdi */
+#define SD_RES_VDI_WRITE     0x0B /* Cannot write requested vdi */
+#define SD_RES_BASE_VDI_READ 0x0C /* Cannot read base vdi */
+#define SD_RES_BASE_VDI_WRITE   0x0D /* Cannot write base vdi */
+#define SD_RES_NO_TAG        0x0E /* Requested tag is not found */
+#define SD_RES_STARTUP       0x0F /* Sheepdog is on starting up */
+#define SD_RES_VDI_NOT_LOCKED   0x10 /* Vdi is not locked */
+#define SD_RES_SHUTDOWN      0x11 /* Sheepdog is shutting down */
+#define SD_RES_NO_MEM        0x12 /* Cannot allocate memory */
+#define SD_RES_FULL_VDI      0x13 /* we already have the maximum vdis */
+#define SD_RES_VER_MISMATCH  0x14 /* Protocol version mismatch */
+#define SD_RES_NO_SPACE      0x15 /* Server has no room for new objects */
+#define SD_RES_WAIT_FOR_FORMAT  0x16 /* Waiting for a format operation */
+#define SD_RES_WAIT_FOR_JOIN    0x17 /* Waiting for other nodes joining */
+#define SD_RES_JOIN_FAILED   0x18 /* Target node had failed to join sheepdog */
+
+/*
+ * Object ID rules
+ *
+ *  0 - 19 (20 bits): data object space
+ * 20 - 31 (12 bits): reserved data object space
+ * 32 - 55 (24 bits): vdi object space
+ * 56 - 59 ( 4 bits): reserved vdi object space
+ * 60 - 63 ( 4 bits): object type indentifier space
+ */
+
+#define VDI_SPACE_SHIFT   32
+#define VDI_BIT (UINT64_C(1) << 63)
+#define VMSTATE_BIT (UINT64_C(1) << 62)
+#define MAX_DATA_OBJS (UINT64_C(1) << 20)
+#define MAX_CHILDREN 1024
+#define SD_MAX_VDI_LEN 256
+#define SD_MAX_VDI_TAG_LEN 256
+#define SD_NR_VDIS   (1U << 24)
+#define SD_DATA_OBJ_SIZE (UINT64_C(1) << 22)
+#define SD_MAX_VDI_SIZE (SD_DATA_OBJ_SIZE * MAX_DATA_OBJS)
+#define SECTOR_SIZE 512
+
+#define SD_INODE_SIZE (sizeof(SheepdogInode))
+#define CURRENT_VDI_ID 0
+
+typedef struct SheepdogReq {
+    uint8_t proto_ver;
+    uint8_t opcode;
+    uint16_t flags;
+    uint32_t epoch;
+    uint32_t id;
+    uint32_t data_length;
+    uint32_t opcode_specific[8];
+} SheepdogReq;
+
+typedef struct SheepdogRsp {
+    uint8_t proto_ver;
+    uint8_t opcode;
+    uint16_t flags;
+    uint32_t epoch;
+    uint32_t id;
+    uint32_t data_length;
+    uint32_t result;
+    uint32_t opcode_specific[7];
+} SheepdogRsp;
+
+typedef struct SheepdogObjReq {
+    uint8_t proto_ver;
+    uint8_t opcode;
+    uint16_t flags;
+    uint32_t epoch;
+    uint32_t id;
+    uint32_t data_length;
+    uint64_t oid;
+    uint64_t cow_oid;
+    uint32_t copies;
+    uint32_t rsvd;
+    uint64_t offset;
+} SheepdogObjReq;
+
+typedef struct SheepdogObjRsp {
+    uint8_t proto_ver;
+    uint8_t opcode;
+    uint16_t flags;
+    uint32_t epoch;
+    uint32_t id;
+    uint32_t data_length;
+    uint32_t result;
+    uint32_t copies;
+    uint32_t pad[6];
+} SheepdogObjRsp;
+
+typedef struct SheepdogVdiReq {
+    uint8_t proto_ver;
+    uint8_t opcode;
+    uint16_t flags;
+    uint32_t epoch;
+    uint32_t id;
+    uint32_t data_length;
+    uint64_t vdi_size;
+    uint32_t base_vdi_id;
+    uint32_t copies;
+    uint32_t snapid;
+    uint32_t pad[3];
+} SheepdogVdiReq;
+
+typedef struct SheepdogVdiRsp {
+    uint8_t proto_ver;
+    uint8_t opcode;
+    uint16_t flags;
+    uint32_t epoch;
+    uint32_t id;
+    uint32_t data_length;
+    uint32_t result;
+    uint32_t rsvd;
+    uint32_t vdi_id;
+    uint32_t pad[5];
+} SheepdogVdiRsp;
+
+typedef struct SheepdogInode {
+    char name[SD_MAX_VDI_LEN];
+    char tag[SD_MAX_VDI_TAG_LEN];
+    uint64_t ctime;
+    uint64_t snap_ctime;
+    uint64_t vm_clock_nsec;
+    uint64_t vdi_size;
+    uint64_t vm_state_size;
+    uint16_t copy_policy;
+    uint8_t nr_copies;
+    uint8_t block_size_shift;
+    uint32_t snap_id;
+    uint32_t vdi_id;
+    uint32_t parent_vdi_id;
+    uint32_t child_vdi_id[MAX_CHILDREN];
+    uint32_t data_vdi_id[MAX_DATA_OBJS];
+} SheepdogInode;
+
+/*
+ * 64 bit FNV-1a non-zero initial basis
+ */
+#define FNV1A_64_INIT ((uint64_t)0xcbf29ce484222325ULL)
+
+/*
+ * 64 bit Fowler/Noll/Vo FNV-1a hash code
+ */
+static inline uint64_t fnv_64a_buf(void *buf, size_t len, uint64_t hval)
+{
+    unsigned char *bp = buf;
+    unsigned char *be = bp + len;
+    while (bp < be) {
+        hval ^= (uint64_t) *bp++;
+        hval += (hval << 1) + (hval << 4) + (hval << 5) +
+            (hval << 7) + (hval << 8) + (hval << 40);
+    }
+    return hval;
+}
+
+static inline int is_data_obj_writeable(SheepdogInode *inode, unsigned int idx)
+{
+    return inode->vdi_id == inode->data_vdi_id[idx];
+}
+
+static inline int is_data_obj(uint64_t oid)
+{
+    return !(VDI_BIT & oid);
+}
+
+static inline uint64_t data_oid_to_idx(uint64_t oid)
+{
+    return oid & (MAX_DATA_OBJS - 1);
+}
+
+static inline uint64_t vid_to_vdi_oid(uint32_t vid)
+{
+    return VDI_BIT | ((uint64_t)vid << VDI_SPACE_SHIFT);
+}
+
+static inline uint64_t vid_to_vmstate_oid(uint32_t vid, uint32_t idx)
+{
+    return VMSTATE_BIT | ((uint64_t)vid << VDI_SPACE_SHIFT) | idx;
+}
+
+static inline uint64_t vid_to_data_oid(uint32_t vid, uint32_t idx)
+{
+    return ((uint64_t)vid << VDI_SPACE_SHIFT) | idx;
+}
+
+static inline int is_snapshot(struct SheepdogInode *inode)
+{
+    return !!inode->snap_ctime;
+}
+
+#undef dprintf
+#ifdef DEBUG_SDOG
+#define dprintf(fmt, args...)                                       \
+    do {                                                            \
+        fprintf(stdout, "%s %d: " fmt, __func__, __LINE__, ##args); \
+    } while (0)
+#else
+#define dprintf(fmt, args...)
+#endif
+
+typedef struct SheepdogAIOCB SheepdogAIOCB;
+
+typedef struct AIOReq {
+    SheepdogAIOCB *aiocb;
+    unsigned int iov_offset;
+
+    uint64_t oid;
+    uint64_t base_oid;
+    uint64_t offset;
+    unsigned int data_len;
+    uint8_t flags;
+    uint32_t id;
+
+    QLIST_ENTRY(AIOReq) outstanding_aio_siblings;
+    QLIST_ENTRY(AIOReq) aioreq_siblings;
+} AIOReq;
+
+enum AIOCBState {
+    AIOCB_WRITE_UDATA,
+    AIOCB_READ_UDATA,
+};
+
+struct SheepdogAIOCB {
+    BlockDriverAIOCB common;
+
+    QEMUIOVector *qiov;
+
+    int64_t sector_num;
+    int nb_sectors;
+
+    int ret;
+    enum AIOCBState aiocb_type;
+
+    QEMUBH *bh;
+    void (*aio_done_func)(SheepdogAIOCB *);
+
+    int canceled;
+
+    QLIST_HEAD(aioreq_head, AIOReq) aioreq_head;
+};
+
+typedef struct BDRVSheepdogState {
+    SheepdogInode inode;
+
+    uint32_t min_dirty_data_idx;
+    uint32_t max_dirty_data_idx;
+
+    char name[SD_MAX_VDI_LEN];
+    int is_snapshot;
+
+    char *addr;
+    char *port;
+    int fd;
+
+    uint32_t aioreq_seq_num;
+    QLIST_HEAD(outstanding_aio_head, AIOReq) outstanding_aio_head;
+} BDRVSheepdogState;
+
+static const char * sd_strerror(int err)
+{
+    int i;
+
+    static const struct {
+        int err;
+        const char *desc;
+    } errors[] = {
+        {SD_RES_SUCCESS, "Success"},
+        {SD_RES_UNKNOWN, "Unknown error"},
+        {SD_RES_NO_OBJ, "No object found"},
+        {SD_RES_EIO, "I/O error"},
+        {SD_RES_VDI_EXIST, "VDI exists already"},
+        {SD_RES_INVALID_PARMS, "Invalid parameters"},
+        {SD_RES_SYSTEM_ERROR, "System error"},
+        {SD_RES_VDI_LOCKED, "VDI is already locked"},
+        {SD_RES_NO_VDI, "No vdi found"},
+        {SD_RES_NO_BASE_VDI, "No base VDI found"},
+        {SD_RES_VDI_READ, "Failed read the requested VDI"},
+        {SD_RES_VDI_WRITE, "Failed to write the requested VDI"},
+        {SD_RES_BASE_VDI_READ, "Failed to read the base VDI"},
+        {SD_RES_BASE_VDI_WRITE, "Failed to write the base VDI"},
+        {SD_RES_NO_TAG, "Failed to find the requested tag"},
+        {SD_RES_STARTUP, "The system is still booting"},
+        {SD_RES_VDI_NOT_LOCKED, "VDI isn't locked"},
+        {SD_RES_SHUTDOWN, "The system is shutting down"},
+        {SD_RES_NO_MEM, "Out of memory on the server"},
+        {SD_RES_FULL_VDI, "We already have the maximum vdis"},
+        {SD_RES_VER_MISMATCH, "Protocol version mismatch"},
+        {SD_RES_NO_SPACE, "Server has no space for new objects"},
+        {SD_RES_WAIT_FOR_FORMAT, "Sheepdog is waiting for a format operation"},
+        {SD_RES_WAIT_FOR_JOIN, "Sheepdog is waiting for other nodes joining"},
+        {SD_RES_JOIN_FAILED, "Target node had failed to join sheepdog"},
+    };
+
+    for (i = 0; i < ARRAY_SIZE(errors); ++i) {
+        if (errors[i].err == err) {
+            return errors[i].desc;
+        }
+    }
+
+    return "Invalid error code";
+}
+
+/*
+ * Sheepdog I/O handling:
+ *
+ * 1. In the sd_aio_readv/writev, read/write requests are added to the
+ *    QEMU Bottom Halves.
+ *
+ * 2. In sd_readv_writev_bh_cb, the callbacks of BHs, we send the I/O
+ *    requests to the server and link the requests to the
+ *    outstanding_list in the BDRVSheepdogState.  we exits the
+ *    function without waiting for receiving the response.
+ *
+ * 3. We receive the response in aio_read_response, the fd handler to
+ *    the sheepdog connection.  If metadata update is needed, we send
+ *    the write request to the vdi object in sd_write_done, the write
+ *    completion function.  The AIOCB callback is not called until all
+ *    the requests belonging to the AIOCB are finished.
+ */
+
+static inline AIOReq *alloc_aio_req(BDRVSheepdogState *s, SheepdogAIOCB *acb,
+                                    uint64_t oid, unsigned int data_len,
+                                    uint64_t offset, uint8_t flags,
+                                    uint64_t base_oid, unsigned int iov_offset)
+{
+    AIOReq *aio_req;
+
+    aio_req = qemu_malloc(sizeof(*aio_req));
+    aio_req->aiocb = acb;
+    aio_req->iov_offset = iov_offset;
+    aio_req->oid = oid;
+    aio_req->base_oid = base_oid;
+    aio_req->offset = offset;
+    aio_req->data_len = data_len;
+    aio_req->flags = flags;
+    aio_req->id = s->aioreq_seq_num++;
+
+    QLIST_INSERT_HEAD(&s->outstanding_aio_head, aio_req,
+                      outstanding_aio_siblings);
+    QLIST_INSERT_HEAD(&acb->aioreq_head, aio_req, aioreq_siblings);
+
+    return aio_req;
+}
+
+static inline int free_aio_req(BDRVSheepdogState *s, AIOReq *aio_req)
+{
+    SheepdogAIOCB *acb = aio_req->aiocb;
+    QLIST_REMOVE(aio_req, outstanding_aio_siblings);
+    QLIST_REMOVE(aio_req, aioreq_siblings);
+    qemu_free(aio_req);
+
+    return !QLIST_EMPTY(&acb->aioreq_head);
+}
+
+static void sd_finish_aiocb(SheepdogAIOCB *acb)
+{
+    if (!acb->canceled) {
+        acb->common.cb(acb->common.opaque, acb->ret);
+    }
+    qemu_aio_release(acb);
+}
+
+static void sd_aio_cancel(BlockDriverAIOCB *blockacb)
+{
+    SheepdogAIOCB *acb = (SheepdogAIOCB *)blockacb;
+
+    /*
+     * Sheepdog cannot cancel the requests which are already sent to
+     * the servers, so we just complete the request with -EIO here.
+     */
+    acb->common.cb(acb->common.opaque, -EIO);
+    acb->canceled = 1;
+}
+
+static AIOPool sd_aio_pool = {
+    .aiocb_size = sizeof(SheepdogAIOCB),
+    .cancel = sd_aio_cancel,
+};
+
+static SheepdogAIOCB *sd_aio_setup(BlockDriverState *bs, QEMUIOVector *qiov,
+                                   int64_t sector_num, int nb_sectors,
+                                   BlockDriverCompletionFunc *cb, void *opaque)
+{
+    SheepdogAIOCB *acb;
+
+    acb = qemu_aio_get(&sd_aio_pool, bs, cb, opaque);
+
+    acb->qiov = qiov;
+
+    acb->sector_num = sector_num;
+    acb->nb_sectors = nb_sectors;
+
+    acb->aio_done_func = NULL;
+    acb->canceled = 0;
+    acb->bh = NULL;
+    acb->ret = 0;
+    QLIST_INIT(&acb->aioreq_head);
+    return acb;
+}
+
+static int sd_schedule_bh(QEMUBHFunc *cb, SheepdogAIOCB *acb)
+{
+    if (acb->bh) {
+        error_report("bug: %d %d\n", acb->aiocb_type, acb->aiocb_type);
+        return -EIO;
+    }
+
+    acb->bh = qemu_bh_new(cb, acb);
+    if (!acb->bh) {
+        error_report("oom: %d %d\n", acb->aiocb_type, acb->aiocb_type);
+        return -EIO;
+    }
+
+    qemu_bh_schedule(acb->bh);
+
+    return 0;
+}
+
+#ifdef _WIN32
+
+struct msghdr {
+    struct iovec *msg_iov;
+    size_t        msg_iovlen;
+};
+
+static ssize_t sendmsg(int s, const struct msghdr *msg, int flags)
+{
+    size_t size = 0;
+    char *buf, *p;
+    int i, ret;
+
+    /* count the msg size */
+    for (i = 0; i < msg->msg_iovlen; i++) {
+        size += msg->msg_iov[i].iov_len;
+    }
+    buf = qemu_malloc(size);
+
+    p = buf;
+    for (i = 0; i < msg->msg_iovlen; i++) {
+        memcpy(p, msg->msg_iov[i].iov_base, msg->msg_iov[i].iov_len);
+        p += msg->msg_iov[i].iov_len;
+    }
+
+    ret = send(s, buf, size, flags);
+
+    qemu_free(buf);
+    return ret;
+}
+
+static ssize_t recvmsg(int s, struct msghdr *msg, int flags)
+{
+    size_t size = 0;
+    char *buf, *p;
+    int i, ret;
+
+    /* count the msg size */
+    for (i = 0; i < msg->msg_iovlen; i++) {
+        size += msg->msg_iov[i].iov_len;
+    }
+    buf = qemu_malloc(size);
+
+    ret = recv(s, buf, size, flags);
+    if (ret < 0) {
+        goto out;
+    }
+
+    p = buf;
+    for (i = 0; i < msg->msg_iovlen; i++) {
+        memcpy(msg->msg_iov[i].iov_base, p, msg->msg_iov[i].iov_len);
+        p += msg->msg_iov[i].iov_len;
+    }
+out:
+    qemu_free(buf);
+    return ret;
+}
+
+#endif
+
+/*
+ * Send/recv data with iovec buffers
+ *
+ * This function send/recv data from/to the iovec buffer directly.
+ * The first `offset' bytes in the iovec buffer are skipped and next
+ * `len' bytes are used.
+ *
+ * For example,
+ *
+ *   do_send_recv(sockfd, iov, len, offset, 1);
+ *
+ * is equals to
+ *
+ *   char *buf = malloc(size);
+ *   iov_to_buf(iov, iovcnt, buf, offset, size);
+ *   send(sockfd, buf, size, 0);
+ *   free(buf);
+ */
+static int do_send_recv(int sockfd, struct iovec *iov, int len, int offset,
+                        int write)
+{
+    struct msghdr msg;
+    int ret, diff;
+
+    memset(&msg, 0, sizeof(msg));
+    msg.msg_iov = iov;
+    msg.msg_iovlen = 1;
+
+    len += offset;
+
+    while (iov->iov_len < len) {
+        len -= iov->iov_len;
+
+        iov++;
+        msg.msg_iovlen++;
+    }
+
+    diff = iov->iov_len - len;
+    iov->iov_len -= diff;
+
+    while (msg.msg_iov->iov_len <= offset) {
+        offset -= msg.msg_iov->iov_len;
+
+        msg.msg_iov++;
+        msg.msg_iovlen--;
+    }
+
+    msg.msg_iov->iov_base = (char *) msg.msg_iov->iov_base + offset;
+    msg.msg_iov->iov_len -= offset;
+
+    if (write) {
+        ret = sendmsg(sockfd, &msg, 0);
+    } else {
+        ret = recvmsg(sockfd, &msg, 0);
+    }
+
+    msg.msg_iov->iov_base = (char *) msg.msg_iov->iov_base - offset;
+    msg.msg_iov->iov_len += offset;
+
+    iov->iov_len += diff;
+    return ret;
+}
+
+static int connect_to_sdog(const char *addr, const char *port)
+{
+    char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
+    int fd, ret;
+    struct addrinfo hints, *res, *res0;
+
+    if (!addr) {
+        addr = SD_DEFAULT_ADDR;
+        port = SD_DEFAULT_PORT;
+    }
+
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_socktype = SOCK_STREAM;
+
+    ret = getaddrinfo(addr, port, &hints, &res0);
+    if (ret) {
+        error_report("unable to get address info %s, %s\n",
+                     addr, strerror(errno));
+        return -1;
+    }
+
+    for (res = res0; res; res = res->ai_next) {
+        ret = getnameinfo(res->ai_addr, res->ai_addrlen, hbuf, sizeof(hbuf),
+                          sbuf, sizeof(sbuf), NI_NUMERICHOST | NI_NUMERICSERV);
+        if (ret) {
+            continue;
+        }
+
+        fd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
+        if (fd < 0) {
+            continue;
+        }
+
+    reconnect:
+        ret = connect(fd, res->ai_addr, res->ai_addrlen);
+        if (ret < 0) {
+            if (errno == EINTR) {
+                goto reconnect;
+            }
+            break;
+        }
+
+        dprintf("connected to %s:%s\n", addr, port);
+        goto success;
+    }
+    fd = -1;
+    error_report("failed connect to %s:%s\n", addr, port);
+success:
+    freeaddrinfo(res0);
+    return fd;
+}
+
+static int do_readv_writev(int sockfd, struct iovec *iov, int len,
+                           int iov_offset, int write)
+{
+    int ret;
+again:
+    ret = do_send_recv(sockfd, iov, len, iov_offset, write);
+    if (ret < 0) {
+        if (errno == EINTR || errno == EAGAIN) {
+            goto again;
+        }
+        error_report("failed to recv a rsp, %s\n", strerror(errno));
+        return 1;
+    }
+
+    iov_offset += ret;
+    len -= ret;
+    if (len) {
+        goto again;
+    }
+
+    return 0;
+}
+
+static int do_readv(int sockfd, struct iovec *iov, int len, int iov_offset)
+{
+    return do_readv_writev(sockfd, iov, len, iov_offset, 0);
+}
+
+static int do_writev(int sockfd, struct iovec *iov, int len, int iov_offset)
+{
+    return do_readv_writev(sockfd, iov, len, iov_offset, 1);
+}
+
+static int do_read_write(int sockfd, void *buf, int len, int write)
+{
+    struct iovec iov;
+
+    iov.iov_base = buf;
+    iov.iov_len = len;
+
+    return do_readv_writev(sockfd, &iov, len, 0, write);
+}
+
+static int do_read(int sockfd, void *buf, int len)
+{
+    return do_read_write(sockfd, buf, len, 0);
+}
+
+static int do_write(int sockfd, void *buf, int len)
+{
+    return do_read_write(sockfd, buf, len, 1);
+}
+
+static int send_req(int sockfd, SheepdogReq *hdr, void *data,
+                    unsigned int *wlen)
+{
+    int ret;
+    struct iovec iov[2];
+
+    iov[0].iov_base = hdr;
+    iov[0].iov_len = sizeof(*hdr);
+
+    if (*wlen) {
+        iov[1].iov_base = data;
+        iov[1].iov_len = *wlen;
+    }
+
+    ret = do_writev(sockfd, iov, sizeof(*hdr) + *wlen, 0);
+    if (ret) {
+        error_report("failed to send a req, %s\n", strerror(errno));
+        ret = -1;
+    }
+
+    return ret;
+}
+
+static int do_req(int sockfd, SheepdogReq *hdr, void *data,
+                  unsigned int *wlen, unsigned int *rlen)
+{
+    int ret;
+
+    ret = send_req(sockfd, hdr, data, wlen);
+    if (ret) {
+        ret = -1;
+        goto out;
+    }
+
+    ret = do_read(sockfd, hdr, sizeof(*hdr));
+    if (ret) {
+        error_report("failed to get a rsp, %s\n", strerror(errno));
+        ret = -1;
+        goto out;
+    }
+
+    if (*rlen > hdr->data_length) {
+        *rlen = hdr->data_length;
+    }
+
+    if (*rlen) {
+        ret = do_read(sockfd, data, *rlen);
+        if (ret) {
+            error_report("failed to get the data, %s\n", strerror(errno));
+            ret = -1;
+            goto out;
+        }
+    }
+    ret = 0;
+out:
+    return ret;
+}
+
+static int add_aio_request(BDRVSheepdogState *s, AIOReq *aio_req,
+                           struct iovec *iov, int niov, int create,
+                           enum AIOCBState aiocb_type);
+
+/*
+ * This function searchs pending requests to the object `oid', and
+ * sends them.
+ */
+static void send_pending_req(BDRVSheepdogState *s, uint64_t oid, uint32_t id)
+{
+    AIOReq *aio_req, *next;
+    SheepdogAIOCB *acb;
+    int ret;
+
+    QLIST_FOREACH_SAFE(aio_req, &s->outstanding_aio_head,
+                       outstanding_aio_siblings, next) {
+        if (id == aio_req->id) {
+            continue;
+        }
+        if (aio_req->oid != oid) {
+            continue;
+        }
+
+        acb = aio_req->aiocb;
+        ret = add_aio_request(s, aio_req, acb->qiov->iov,
+                              acb->qiov->niov, 0, acb->aiocb_type);
+        if (ret < 0) {
+            error_report("add_aio_request is failed\n");
+            free_aio_req(s, aio_req);
+            if (QLIST_EMPTY(&acb->aioreq_head)) {
+                sd_finish_aiocb(acb);
+            }
+        }
+    }
+}
+
+/*
+ * Receive responses of the I/O requests.
+ *
+ * This function is registered as a fd handler, and called from the
+ * main loop when s->fd is ready for reading responses.
+ */
+static void aio_read_response(void *opaque)
+{
+    SheepdogObjRsp rsp;
+    BDRVSheepdogState *s = opaque;
+    int fd = s->fd;
+    int ret;
+    AIOReq *aio_req = NULL;
+    SheepdogAIOCB *acb;
+    int rest;
+    unsigned long idx;
+
+    if (QLIST_EMPTY(&s->outstanding_aio_head)) {
+        return;
+    }
+
+    /* read a header */
+    ret = do_read(fd, &rsp, sizeof(rsp));
+    if (ret) {
+        error_report("failed to get the header, %s\n", strerror(errno));
+        return;
+    }
+
+    /* find the right aio_req from the outstanding_aio list */
+    QLIST_FOREACH(aio_req, &s->outstanding_aio_head, outstanding_aio_siblings) {
+        if (aio_req->id == rsp.id) {
+            break;
+        }
+    }
+    if (!aio_req) {
+        error_report("cannot find aio_req %x\n", rsp.id);
+        return;
+    }
+
+    acb = aio_req->aiocb;
+
+    switch (acb->aiocb_type) {
+    case AIOCB_WRITE_UDATA:
+        if (!is_data_obj(aio_req->oid)) {
+            break;
+        }
+        idx = data_oid_to_idx(aio_req->oid);
+
+        if (s->inode.data_vdi_id[idx] != s->inode.vdi_id) {
+            /*
+             * If the object is newly created one, we need to update
+             * the vdi object (metadata object).  min_dirty_data_idx
+             * and max_dirty_data_idx are changed to include updated
+             * index between them.
+             */
+            s->inode.data_vdi_id[idx] = s->inode.vdi_id;
+            s->max_dirty_data_idx = MAX(idx, s->max_dirty_data_idx);
+            s->min_dirty_data_idx = MIN(idx, s->min_dirty_data_idx);
+
+            /*
+             * Some requests may be blocked because simultaneous
+             * create requests are not allowed, so we search the
+             * pending requests here.
+             */
+            send_pending_req(s, vid_to_data_oid(s->inode.vdi_id, idx), rsp.id);
+        }
+        break;
+    case AIOCB_READ_UDATA:
+        ret = do_readv(fd, acb->qiov->iov, rsp.data_length,
+                       aio_req->iov_offset);
+        if (ret) {
+            error_report("failed to get the data, %s\n", strerror(errno));
+            return;
+        }
+        break;
+    }
+
+    if (rsp.result != SD_RES_SUCCESS) {
+        acb->ret = -EIO;
+        error_report("%s\n", sd_strerror(rsp.result));
+    }
+
+    rest = free_aio_req(s, aio_req);
+    if (!rest) {
+        /*
+         * We've finished all requests which belong to the AIOCB, so
+         * we can call the callback now.
+         */
+        acb->aio_done_func(acb);
+    }
+}
+
+static int aio_flush_request(void *opaque)
+{
+    BDRVSheepdogState *s = opaque;
+
+    return !QLIST_EMPTY(&s->outstanding_aio_head);
+}
+
+#ifdef _WIN32
+
+static int set_cork(int fd, int v)
+{
+    return 0;
+}
+
+#else
+
+static int set_cork(int fd, int v)
+{
+    return setsockopt(fd, SOL_TCP, TCP_CORK, &v, sizeof(v));
+}
+
+#endif
+
+static int set_nodelay(int fd)
+{
+    int ret, opt;
+
+    opt = 1;
+    ret = setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (char *)&opt, sizeof(opt));
+    return ret;
+}
+
+/*
+ * Return a socket discriptor to read/write objects.
+ *
+ * We cannot use this discriptor for other operations because
+ * the block driver may be on waiting response from the server.
+ */
+static int get_sheep_fd(BDRVSheepdogState *s)
+{
+    int ret, fd;
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        error_report("%s\n", strerror(errno));
+        return -1;
+    }
+
+    socket_set_nonblock(fd);
+
+    ret = set_nodelay(fd);
+    if (ret) {
+        error_report("%s\n", strerror(errno));
+        closesocket(fd);
+        return -1;
+    }
+
+    qemu_aio_set_fd_handler(fd, aio_read_response, NULL, aio_flush_request,
+                            NULL, s);
+    return fd;
+}
+
+/*
+ * Parse a filename
+ *
+ * filename must be one of the following formats:
+ *   1. [vdiname]
+ *   2. [vdiname]:[snapid]
+ *   3. [vdiname]:[tag]
+ *   4. [hostname]:[port]:[vdiname]
+ *   5. [hostname]:[port]:[vdiname]:[snapid]
+ *   6. [hostname]:[port]:[vdiname]:[tag]
+ *
+ * You can boot from the snapshot images by specifying `snapid` or
+ * `tag'.
+ *
+ * You can run VMs outside the Sheepdog cluster by specifying
+ * `hostname' and `port' (experimental).
+ */
+static int parse_vdiname(BDRVSheepdogState *s, const char *filename,
+                         char *vdi, uint32_t *snapid, char *tag)
+{
+    char *p, *q;
+    int nr_sep;
+
+    p = q = qemu_strdup(filename);
+
+    /* count the number of separators */
+    nr_sep = 0;
+    while (*p) {
+        if (*p == ':') {
+            nr_sep++;
+        }
+        p++;
+    }
+    p = q;
+
+    /* use the first two tokens as hostname and port number. */
+    if (nr_sep >= 2) {
+        s->addr = p;
+        p = strchr(p, ':');
+        *p++ = '\0';
+
+        s->port = p;
+        p = strchr(p, ':');
+        *p++ = '\0';
+    } else {
+        s->addr = NULL;
+        s->port = 0;
+    }
+
+    strncpy(vdi, p, SD_MAX_VDI_LEN);
+
+    p = strchr(vdi, ':');
+    if (p) {
+        *p++ = '\0';
+        *snapid = strtoul(p, NULL, 10);
+        if (*snapid == 0) {
+            strncpy(tag, p, SD_MAX_VDI_TAG_LEN);
+        }
+    } else {
+        *snapid = CURRENT_VDI_ID; /* search current vdi */
+    }
+
+    if (s->addr == NULL) {
+        qemu_free(q);
+    }
+
+    return 0;
+}
+
+static int find_vdi_name(BDRVSheepdogState *s, char *filename, uint32_t snapid,
+                         char *tag, uint32_t *vid, int for_snapshot)
+{
+    int ret, fd;
+    SheepdogVdiReq hdr;
+    SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
+    unsigned int wlen, rlen = 0;
+    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        return -1;
+    }
+
+    memset(buf, 0, sizeof(buf));
+    strncpy(buf, filename, SD_MAX_VDI_LEN);
+    strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
+
+    memset(&hdr, 0, sizeof(hdr));
+    if (for_snapshot) {
+        hdr.opcode = SD_OP_GET_VDI_INFO;
+    } else {
+        hdr.opcode = SD_OP_LOCK_VDI;
+    }
+    wlen = SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN;
+    hdr.proto_ver = SD_PROTO_VER;
+    hdr.data_length = wlen;
+    hdr.snapid = snapid;
+    hdr.flags = SD_FLAG_CMD_WRITE;
+
+    ret = do_req(fd, (SheepdogReq *)&hdr, buf, &wlen, &rlen);
+    if (ret) {
+        ret = -1;
+        goto out;
+    }
+
+    if (rsp->result != SD_RES_SUCCESS) {
+        error_report("cannot get vdi info, %s, %s %d %s\n",
+                     sd_strerror(rsp->result), filename, snapid, tag);
+        ret = -1;
+        goto out;
+    }
+    *vid = rsp->vdi_id;
+
+    ret = 0;
+out:
+    closesocket(fd);
+    return ret;
+}
+
+static int add_aio_request(BDRVSheepdogState *s, AIOReq *aio_req,
+                           struct iovec *iov, int niov, int create,
+                           enum AIOCBState aiocb_type)
+{
+    int nr_copies = s->inode.nr_copies;
+    SheepdogObjReq hdr;
+    unsigned int wlen;
+    int ret;
+    uint64_t oid = aio_req->oid;
+    unsigned int datalen = aio_req->data_len;
+    uint64_t offset = aio_req->offset;
+    uint8_t flags = aio_req->flags;
+    uint64_t old_oid = aio_req->base_oid;
+
+    if (!nr_copies) {
+        error_report("bug\n");
+    }
+
+    memset(&hdr, 0, sizeof(hdr));
+
+    if (aiocb_type == AIOCB_READ_UDATA) {
+        wlen = 0;
+        hdr.opcode = SD_OP_READ_OBJ;
+        hdr.flags = flags;
+    } else if (create) {
+        wlen = datalen;
+        hdr.opcode = SD_OP_CREATE_AND_WRITE_OBJ;
+        hdr.flags = SD_FLAG_CMD_WRITE | flags;
+    } else {
+        wlen = datalen;
+        hdr.opcode = SD_OP_WRITE_OBJ;
+        hdr.flags = SD_FLAG_CMD_WRITE | flags;
+    }
+
+    hdr.oid = oid;
+    hdr.cow_oid = old_oid;
+    hdr.copies = s->inode.nr_copies;
+
+    hdr.data_length = datalen;
+    hdr.offset = offset;
+
+    hdr.id = aio_req->id;
+
+    set_cork(s->fd, 1);
+
+    /* send a header */
+    ret = do_write(s->fd, &hdr, sizeof(hdr));
+    if (ret) {
+        error_report("failed to send a req, %s\n", strerror(errno));
+        return -EIO;
+    }
+
+    if (wlen) {
+        ret = do_writev(s->fd, iov, wlen, aio_req->iov_offset);
+        if (ret) {
+            error_report("failed to send a data, %s\n", strerror(errno));
+            return -EIO;
+        }
+    }
+
+    set_cork(s->fd, 0);
+
+    return 0;
+}
+
+static int read_write_object(int fd, char *buf, uint64_t oid, int copies,
+                             unsigned int datalen, uint64_t offset,
+                             int write, int create)
+{
+    SheepdogObjReq hdr;
+    SheepdogObjRsp *rsp = (SheepdogObjRsp *)&hdr;
+    unsigned int wlen, rlen;
+    int ret;
+
+    memset(&hdr, 0, sizeof(hdr));
+
+    if (write) {
+        wlen = datalen;
+        rlen = 0;
+        hdr.flags = SD_FLAG_CMD_WRITE;
+        if (create) {
+            hdr.opcode = SD_OP_CREATE_AND_WRITE_OBJ;
+        } else {
+            hdr.opcode = SD_OP_WRITE_OBJ;
+        }
+    } else {
+        wlen = 0;
+        rlen = datalen;
+        hdr.opcode = SD_OP_READ_OBJ;
+    }
+    hdr.oid = oid;
+    hdr.data_length = datalen;
+    hdr.offset = offset;
+    hdr.copies = copies;
+
+    ret = do_req(fd, (SheepdogReq *)&hdr, buf, &wlen, &rlen);
+    if (ret) {
+        error_report("failed to send a request to the sheep\n");
+        return -1;
+    }
+
+    switch (rsp->result) {
+    case SD_RES_SUCCESS:
+        return 0;
+    default:
+        error_report("%s\n", sd_strerror(rsp->result));
+        return -1;
+    }
+}
+
+static int read_object(int fd, char *buf, uint64_t oid, int copies,
+                       unsigned int datalen, uint64_t offset)
+{
+    return read_write_object(fd, buf, oid, copies, datalen, offset, 0, 0);
+}
+
+static int write_object(int fd, char *buf, uint64_t oid, int copies,
+                        unsigned int datalen, uint64_t offset, int create)
+{
+    return read_write_object(fd, buf, oid, copies, datalen, offset, 1, create);
+}
+
+static int sd_open(BlockDriverState *bs, const char *filename, int flags)
+{
+    int ret, fd;
+    uint32_t vid = 0;
+    BDRVSheepdogState *s = bs->opaque;
+    char vdi[SD_MAX_VDI_LEN], tag[SD_MAX_VDI_TAG_LEN];
+    uint32_t snapid;
+    char *buf = NULL;
+
+    strstart(filename, "sheepdog:", (const char **)&filename);
+
+    QLIST_INIT(&s->outstanding_aio_head);
+    s->fd = -1;
+
+    memset(vdi, 0, sizeof(vdi));
+    memset(tag, 0, sizeof(tag));
+    if (parse_vdiname(s, filename, vdi, &snapid, tag) < 0) {
+        goto out;
+    }
+    s->fd = get_sheep_fd(s);
+    if (s->fd < 0) {
+        goto out;
+    }
+
+    ret = find_vdi_name(s, vdi, snapid, tag, &vid, 0);
+    if (ret) {
+        goto out;
+    }
+
+    if (snapid) {
+        dprintf("%" PRIx32 " snapshot inode was open.\n", vid);
+        s->is_snapshot = 1;
+    }
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        error_report("failed to connect\n");
+        goto out;
+    }
+
+    buf = qemu_malloc(SD_INODE_SIZE);
+    ret = read_object(fd, buf, vid_to_vdi_oid(vid), 0, SD_INODE_SIZE, 0);
+
+    closesocket(fd);
+
+    if (ret) {
+        goto out;
+    }
+
+    memcpy(&s->inode, buf, sizeof(s->inode));
+    s->min_dirty_data_idx = UINT32_MAX;
+    s->max_dirty_data_idx = 0;
+
+    bs->total_sectors = s->inode.vdi_size / SECTOR_SIZE;
+    strncpy(s->name, vdi, sizeof(s->name));
+    qemu_free(buf);
+    return 0;
+out:
+    qemu_aio_set_fd_handler(s->fd, NULL, NULL, NULL, NULL, NULL);
+    if (s->fd >= 0) {
+        closesocket(s->fd);
+    }
+    qemu_free(buf);
+    return -1;
+}
+
+static int do_sd_create(char *filename, int64_t vdi_size,
+                        uint32_t base_vid, uint32_t *vdi_id, int snapshot,
+                        const char *addr, const char *port)
+{
+    SheepdogVdiReq hdr;
+    SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
+    int fd, ret;
+    unsigned int wlen, rlen = 0;
+    char buf[SD_MAX_VDI_LEN];
+
+    fd = connect_to_sdog(addr, port);
+    if (fd < 0) {
+        return -EIO;
+    }
+
+    memset(buf, 0, sizeof(buf));
+    strncpy(buf, filename, SD_MAX_VDI_LEN);
+
+    memset(&hdr, 0, sizeof(hdr));
+    hdr.opcode = SD_OP_NEW_VDI;
+    hdr.base_vdi_id = base_vid;
+
+    wlen = SD_MAX_VDI_LEN;
+
+    hdr.flags = SD_FLAG_CMD_WRITE;
+    hdr.snapid = snapshot;
+
+    hdr.data_length = wlen;
+    hdr.vdi_size = vdi_size;
+
+    ret = do_req(fd, (SheepdogReq *)&hdr, buf, &wlen, &rlen);
+
+    closesocket(fd);
+
+    if (ret) {
+        return -EIO;
+    }
+
+    if (rsp->result != SD_RES_SUCCESS) {
+        error_report("%s, %s\n", sd_strerror(rsp->result), filename);
+        return -EIO;
+    }
+
+    if (vdi_id) {
+        *vdi_id = rsp->vdi_id;
+    }
+
+    return 0;
+}
+
+static int sd_create(const char *filename, QEMUOptionParameter *options)
+{
+    int ret;
+    uint32_t vid = 0;
+    int64_t vdi_size = 0;
+    char *backing_file = NULL;
+
+    strstart(filename, "sheepdog:", (const char **)&filename);
+
+    while (options && options->name) {
+        if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
+            vdi_size = options->value.n;
+        } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
+            backing_file = options->value.s;
+        }
+        options++;
+    }
+
+    if (vdi_size > SD_MAX_VDI_SIZE) {
+        error_report("too big image size\n");
+        return -EINVAL;
+    }
+
+    if (backing_file) {
+        BlockDriverState *bs;
+        BDRVSheepdogState *s;
+        BlockDriver *drv;
+
+        /* Currently, only Sheepdog backing image is supported. */
+        drv = bdrv_find_protocol(backing_file);
+        if (!drv || strcmp(drv->protocol_name, "sheepdog") != 0) {
+            error_report("backing_file must be a sheepdog image\n");
+            return -EINVAL;
+        }
+
+        ret = bdrv_file_open(&bs, backing_file, 0);
+        if (ret < 0)
+            return -EIO;
+
+        s = bs->opaque;
+
+        if (!is_snapshot(&s->inode)) {
+            error_report("cannot clone from a non snapshot vdi\n");
+            bdrv_delete(bs);
+            return -EINVAL;
+        }
+
+        vid = s->inode.vdi_id;
+        bdrv_delete(bs);
+    }
+
+    return do_sd_create((char *)filename, vdi_size, vid, NULL, 0, NULL, NULL);
+}
+
+static void sd_close(BlockDriverState *bs)
+{
+    BDRVSheepdogState *s = bs->opaque;
+    SheepdogVdiReq hdr;
+    SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
+    unsigned int wlen, rlen = 0;
+    int fd, ret;
+
+    dprintf("%s\n", s->name);
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        return;
+    }
+
+    memset(&hdr, 0, sizeof(hdr));
+
+    hdr.opcode = SD_OP_RELEASE_VDI;
+    wlen = strlen(s->name) + 1;
+    hdr.data_length = wlen;
+    hdr.flags = SD_FLAG_CMD_WRITE;
+
+    ret = do_req(fd, (SheepdogReq *)&hdr, s->name, &wlen, &rlen);
+
+    closesocket(fd);
+
+    if (!ret && rsp->result != SD_RES_SUCCESS &&
+        rsp->result != SD_RES_VDI_NOT_LOCKED) {
+        error_report("%s, %s\n", sd_strerror(rsp->result), s->name);
+    }
+
+    qemu_aio_set_fd_handler(s->fd, NULL, NULL, NULL, NULL, NULL);
+    closesocket(s->fd);
+    qemu_free(s->addr);
+}
+
+static int64_t sd_getlength(BlockDriverState *bs)
+{
+    BDRVSheepdogState *s = bs->opaque;
+
+    return s->inode.vdi_size;
+}
+
+static int sd_truncate(BlockDriverState *bs, int64_t offset)
+{
+    BDRVSheepdogState *s = bs->opaque;
+    int ret, fd;
+    unsigned int datalen;
+
+    if (offset < s->inode.vdi_size) {
+        error_report("shrinking is not supported\n");
+        return -EINVAL;
+    } else if (offset > SD_MAX_VDI_SIZE) {
+        error_report("too big image size\n");
+        return -EINVAL;
+    }
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        return -EIO;
+    }
+
+    /* we don't need to update entire object */
+    datalen = SD_INODE_SIZE - sizeof(s->inode.data_vdi_id);
+    s->inode.vdi_size = offset;
+    ret = write_object(fd, (char *)&s->inode, vid_to_vdi_oid(s->inode.vdi_id),
+                       s->inode.nr_copies, datalen, 0, 0);
+    close(fd);
+
+    if (ret < 0) {
+        error_report("failed to update an inode.\n");
+        return -EIO;
+    }
+
+    return 0;
+}
+
+/*
+ * This function is called after writing data objects.  If we need to
+ * update metadata, this sends a write request to the vdi object.
+ * Otherwise, this calls the AIOCB callback.
+ */
+static void sd_write_done(SheepdogAIOCB *acb)
+{
+    int ret;
+    BDRVSheepdogState *s = acb->common.bs->opaque;
+    struct iovec iov;
+    AIOReq *aio_req;
+    uint32_t offset, data_len, mn, mx;
+
+    mn = s->min_dirty_data_idx;
+    mx = s->max_dirty_data_idx;
+    if (mn <= mx) {
+        /* we need to update the vdi object. */
+        offset = sizeof(s->inode) - sizeof(s->inode.data_vdi_id) +
+            mn * sizeof(s->inode.data_vdi_id[0]);
+        data_len = (mx - mn + 1) * sizeof(s->inode.data_vdi_id[0]);
+
+        s->min_dirty_data_idx = UINT32_MAX;
+        s->max_dirty_data_idx = 0;
+
+        iov.iov_base = &s->inode;
+        iov.iov_len = sizeof(s->inode);
+        aio_req = alloc_aio_req(s, acb, vid_to_vdi_oid(s->inode.vdi_id),
+                                data_len, offset, 0, 0, offset);
+        ret = add_aio_request(s, aio_req, &iov, 1, 0, AIOCB_WRITE_UDATA);
+        if (ret) {
+            free_aio_req(s, aio_req);
+            acb->ret = -EIO;
+            goto out;
+        }
+
+        acb->aio_done_func = sd_finish_aiocb;
+        acb->aiocb_type = AIOCB_WRITE_UDATA;
+        return;
+    }
+out:
+    sd_finish_aiocb(acb);
+}
+
+/*
+ * Create a writable VDI from a snapshot
+ */
+static int sd_create_branch(BDRVSheepdogState *s)
+{
+    int ret, fd;
+    uint32_t vid;
+    char *buf;
+
+    dprintf("%" PRIx32 " is snapshot.\n", s->inode.vdi_id);
+
+    buf = qemu_malloc(SD_INODE_SIZE);
+
+    ret = do_sd_create(s->name, s->inode.vdi_size, s->inode.vdi_id, &vid, 1,
+                       s->addr, s->port);
+    if (ret) {
+        goto out;
+    }
+
+    dprintf("%" PRIx32 " is created.\n", vid);
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        error_report("failed to connect\n");
+        goto out;
+    }
+
+    ret = read_object(fd, buf, vid_to_vdi_oid(vid), s->inode.nr_copies,
+                      SD_INODE_SIZE, 0);
+
+    closesocket(fd);
+
+    if (ret < 0) {
+        goto out;
+    }
+
+    memcpy(&s->inode, buf, sizeof(s->inode));
+
+    s->is_snapshot = 0;
+    ret = 0;
+    dprintf("%" PRIx32 " was newly created.\n", s->inode.vdi_id);
+
+out:
+    qemu_free(buf);
+
+    return ret;
+}
+
+/*
+ * Send I/O requests to the server.
+ *
+ * This function sends requests to the server, links the requests to
+ * the outstanding_list in BDRVSheepdogState, and exits without
+ * waiting the response.  The responses are received in the
+ * `aio_read_response' function which is called from the main loop as
+ * a fd handler.
+ */
+static void sd_readv_writev_bh_cb(void *p)
+{
+    SheepdogAIOCB *acb = p;
+    int ret = 0;
+    unsigned long len, done = 0, total = acb->nb_sectors * SECTOR_SIZE;
+    unsigned long idx = acb->sector_num * SECTOR_SIZE / SD_DATA_OBJ_SIZE;
+    uint64_t oid;
+    uint64_t offset = (acb->sector_num * SECTOR_SIZE) % SD_DATA_OBJ_SIZE;
+    BDRVSheepdogState *s = acb->common.bs->opaque;
+    SheepdogInode *inode = &s->inode;
+    AIOReq *aio_req;
+
+    qemu_bh_delete(acb->bh);
+    acb->bh = NULL;
+
+    if (acb->aiocb_type == AIOCB_WRITE_UDATA && s->is_snapshot) {
+        /*
+         * In the case we open the snapshot VDI, Sheepdog creates the
+         * writable VDI when we do a write operation first.
+         */
+        ret = sd_create_branch(s);
+        if (ret) {
+            acb->ret = -EIO;
+            goto out;
+        }
+    }
+
+    while (done != total) {
+        uint8_t flags = 0;
+        uint64_t old_oid = 0;
+        int create = 0;
+
+        oid = vid_to_data_oid(inode->data_vdi_id[idx], idx);
+
+        len = MIN(total - done, SD_DATA_OBJ_SIZE - offset);
+
+        if (!inode->data_vdi_id[idx]) {
+            if (acb->aiocb_type == AIOCB_READ_UDATA) {
+                goto done;
+            }
+
+            create = 1;
+        } else if (acb->aiocb_type == AIOCB_WRITE_UDATA
+                   && !is_data_obj_writeable(inode, idx)) {
+            /* Copy-On-Write */
+            create = 1;
+            old_oid = oid;
+            flags = SD_FLAG_CMD_COW;
+        }
+
+        if (create) {
+            dprintf("update ino (%" PRIu32") %" PRIu64 " %" PRIu64
+                    " %" PRIu64 "\n", inode->vdi_id, oid,
+                    vid_to_data_oid(inode->data_vdi_id[idx], idx), idx);
+            oid = vid_to_data_oid(inode->vdi_id, idx);
+            dprintf("new oid %lx\n", oid);
+        }
+
+        aio_req = alloc_aio_req(s, acb, oid, len, offset, flags, old_oid, done);
+
+        if (create) {
+            AIOReq *areq;
+            QLIST_FOREACH(areq, &s->outstanding_aio_head,
+                          outstanding_aio_siblings) {
+                if (areq == aio_req) {
+                    continue;
+                }
+                if (areq->oid == oid) {
+                    /*
+                     * Sheepdog cannot handle simultaneous create
+                     * requests to the same object.  So we cannot send
+                     * the request until the previous request
+                     * finishes.
+                     */
+                    aio_req->flags = 0;
+                    aio_req->base_oid = 0;
+                    goto done;
+                }
+            }
+        }
+
+        ret = add_aio_request(s, aio_req, acb->qiov->iov, acb->qiov->niov,
+                              create, acb->aiocb_type);
+        if (ret < 0) {
+            error_report("add_aio_request is failed\n");
+            free_aio_req(s, aio_req);
+            acb->ret = -EIO;
+            goto out;
+        }
+    done:
+        offset = 0;
+        idx++;
+        done += len;
+    }
+out:
+    if (QLIST_EMPTY(&acb->aioreq_head)) {
+        sd_finish_aiocb(acb);
+    }
+}
+
+static BlockDriverAIOCB *sd_aio_writev(BlockDriverState *bs, int64_t sector_num,
+                                       QEMUIOVector *qiov, int nb_sectors,
+                                       BlockDriverCompletionFunc *cb,
+                                       void *opaque)
+{
+    SheepdogAIOCB *acb;
+
+    if (bs->growable && sector_num + nb_sectors > bs->total_sectors) {
+        /* TODO: shouldn't block here */
+        if (sd_truncate(bs, (sector_num + nb_sectors) * SECTOR_SIZE) < 0) {
+            return NULL;
+        }
+        bs->total_sectors = sector_num + nb_sectors;
+    }
+
+    acb = sd_aio_setup(bs, qiov, sector_num, nb_sectors, cb, opaque);
+    acb->aio_done_func = sd_write_done;
+    acb->aiocb_type = AIOCB_WRITE_UDATA;
+
+    sd_schedule_bh(sd_readv_writev_bh_cb, acb);
+    return &acb->common;
+}
+
+static BlockDriverAIOCB *sd_aio_readv(BlockDriverState *bs, int64_t sector_num,
+                                      QEMUIOVector *qiov, int nb_sectors,
+                                      BlockDriverCompletionFunc *cb,
+                                      void *opaque)
+{
+    SheepdogAIOCB *acb;
+    int i;
+
+    acb = sd_aio_setup(bs, qiov, sector_num, nb_sectors, cb, opaque);
+    acb->aiocb_type = AIOCB_READ_UDATA;
+    acb->aio_done_func = sd_finish_aiocb;
+
+    /*
+     * TODO: we can do better; we don't need to initialize
+     * blindly.
+     */
+    for (i = 0; i < qiov->niov; i++) {
+        memset(qiov->iov[i].iov_base, 0, qiov->iov[i].iov_len);
+    }
+
+    sd_schedule_bh(sd_readv_writev_bh_cb, acb);
+    return &acb->common;
+}
+
+static int sd_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
+{
+    BDRVSheepdogState *s = bs->opaque;
+    int ret, fd;
+    uint32_t new_vid;
+    SheepdogInode *inode;
+    unsigned int datalen;
+
+    dprintf("sn_info: name %s id_str %s s: name %s vm_state_size %d "
+            "is_snapshot %d\n", sn_info->name, sn_info->id_str,
+            s->name, sn_info->vm_state_size, s->is_snapshot);
+
+    if (s->is_snapshot) {
+        error_report("You can't create a snapshot of a snapshot VDI, "
+                     "%s (%" PRIu32 ").\n", s->name, s->inode.vdi_id);
+
+        return -EINVAL;
+    }
+
+    dprintf("%s %s\n", sn_info->name, sn_info->id_str);
+
+    s->inode.vm_state_size = sn_info->vm_state_size;
+    s->inode.vm_clock_nsec = sn_info->vm_clock_nsec;
+    strncpy(s->inode.tag, sn_info->name, sizeof(s->inode.tag));
+    /* we don't need to update entire object */
+    datalen = SD_INODE_SIZE - sizeof(s->inode.data_vdi_id);
+
+    /* refresh inode. */
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        ret = -EIO;
+        goto cleanup;
+    }
+
+    ret = write_object(fd, (char *)&s->inode, vid_to_vdi_oid(s->inode.vdi_id),
+                       s->inode.nr_copies, datalen, 0, 0);
+    if (ret < 0) {
+        error_report("failed to write snapshot's inode.\n");
+        ret = -EIO;
+        goto cleanup;
+    }
+
+    ret = do_sd_create(s->name, s->inode.vdi_size, s->inode.vdi_id, &new_vid, 1,
+                       s->addr, s->port);
+    if (ret < 0) {
+        error_report("failed to create inode for snapshot. %s\n",
+                     strerror(errno));
+        ret = -EIO;
+        goto cleanup;
+    }
+
+    inode = (SheepdogInode *)qemu_malloc(datalen);
+
+    ret = read_object(fd, (char *)inode, vid_to_vdi_oid(new_vid),
+                      s->inode.nr_copies, datalen, 0);
+
+    if (ret < 0) {
+        error_report("failed to read new inode info. %s\n", strerror(errno));
+        ret = -EIO;
+        goto cleanup;
+    }
+
+    memcpy(&s->inode, inode, datalen);
+    dprintf("s->inode: name %s snap_id %x oid %x\n",
+            s->inode.name, s->inode.snap_id, s->inode.vdi_id);
+
+cleanup:
+    closesocket(fd);
+    return ret;
+}
+
+static int sd_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
+{
+    BDRVSheepdogState *s = bs->opaque;
+    BDRVSheepdogState *old_s;
+    char vdi[SD_MAX_VDI_LEN], tag[SD_MAX_VDI_TAG_LEN];
+    char *buf = NULL;
+    uint32_t vid;
+    uint32_t snapid = 0;
+    int ret = -ENOENT, fd;
+
+    old_s = qemu_malloc(sizeof(BDRVSheepdogState));
+
+    memcpy(old_s, s, sizeof(BDRVSheepdogState));
+
+    memset(vdi, 0, sizeof(vdi));
+    strncpy(vdi, s->name, sizeof(vdi));
+
+    memset(tag, 0, sizeof(tag));
+    snapid = strtoul(snapshot_id, NULL, 10);
+    if (!snapid) {
+        strncpy(tag, s->name, sizeof(tag));
+    }
+
+    ret = find_vdi_name(s, vdi, snapid, tag, &vid, 1);
+    if (ret) {
+        error_report("Failed to find_vdi_name\n");
+        ret = -ENOENT;
+        goto out;
+    }
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        error_report("failed to connect\n");
+        goto out;
+    }
+
+    buf = qemu_malloc(SD_INODE_SIZE);
+    ret = read_object(fd, buf, vid_to_vdi_oid(vid), s->inode.nr_copies,
+                      SD_INODE_SIZE, 0);
+
+    closesocket(fd);
+
+    if (ret) {
+        ret = -ENOENT;
+        goto out;
+    }
+
+    memcpy(&s->inode, buf, sizeof(s->inode));
+
+    if (!s->inode.vm_state_size) {
+        error_report("Invalid snapshot\n");
+        ret = -ENOENT;
+        goto out;
+    }
+
+    s->is_snapshot = 1;
+
+    qemu_free(buf);
+    qemu_free(old_s);
+
+    return 0;
+out:
+    /* recover bdrv_sd_state */
+    memcpy(s, old_s, sizeof(BDRVSheepdogState));
+    qemu_free(buf);
+    qemu_free(old_s);
+
+    error_report("failed to open. recover old bdrv_sd_state.\n");
+
+    return ret;
+}
+
+static int sd_snapshot_delete(BlockDriverState *bs, const char *snapshot_id)
+{
+    /* FIXME: Delete specified snapshot id.  */
+    return 0;
+}
+
+#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
+#define BITS_PER_BYTE        8
+#define BITS_TO_LONGS(nr)    DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
+#define DECLARE_BITMAP(name,bits)               \
+    unsigned long name[BITS_TO_LONGS(bits)]
+
+#define BITS_PER_LONG (BITS_PER_BYTE * sizeof(long))
+
+static inline int test_bit(unsigned int nr, const unsigned long *addr)
+{
+    return ((1UL << (nr % BITS_PER_LONG)) &
+            (((unsigned long *)addr)[nr / BITS_PER_LONG])) != 0;
+}
+
+static int sd_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
+{
+    BDRVSheepdogState *s = bs->opaque;
+    SheepdogReq req;
+    int fd, nr = 1024, ret, max = BITS_TO_LONGS(SD_NR_VDIS) * sizeof(long);
+    QEMUSnapshotInfo *sn_tab = NULL;
+    unsigned wlen, rlen;
+    int found = 0;
+    static SheepdogInode inode;
+    unsigned long *vdi_inuse;
+    unsigned int start_nr;
+    uint64_t hval;
+    uint32_t vid;
+
+    vdi_inuse = qemu_malloc(max);
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        goto out;
+    }
+
+    rlen = max;
+    wlen = 0;
+
+    memset(&req, 0, sizeof(req));
+
+    req.opcode = SD_OP_READ_VDIS;
+    req.data_length = max;
+
+    ret = do_req(fd, (SheepdogReq *)&req, vdi_inuse, &wlen, &rlen);
+
+    closesocket(fd);
+    if (ret) {
+        goto out;
+    }
+
+    sn_tab = qemu_mallocz(nr * sizeof(*sn_tab));
+
+    /* calculate a vdi id with hash function */
+    hval = fnv_64a_buf(s->name, strlen(s->name), FNV1A_64_INIT);
+    start_nr = hval & (SD_NR_VDIS - 1);
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        error_report("failed to connect\n");
+        goto out;
+    }
+
+    for (vid = start_nr; found < nr; vid = (vid + 1) % SD_NR_VDIS) {
+        if (!test_bit(vid, vdi_inuse)) {
+            break;
+        }
+
+        /* we don't need to read entire object */
+        ret = read_object(fd, (char *)&inode, vid_to_vdi_oid(vid),
+                          0, SD_INODE_SIZE - sizeof(inode.data_vdi_id), 0);
+
+        if (ret) {
+            continue;
+        }
+
+        if (!strcmp(inode.name, s->name) && is_snapshot(&inode)) {
+            sn_tab[found].date_sec = inode.snap_ctime >> 32;
+            sn_tab[found].date_nsec = inode.snap_ctime & 0xffffffff;
+            sn_tab[found].vm_state_size = inode.vm_state_size;
+            sn_tab[found].vm_clock_nsec = inode.vm_clock_nsec;
+
+            snprintf(sn_tab[found].id_str, sizeof(sn_tab[found].id_str), "%u",
+                     inode.snap_id);
+            strncpy(sn_tab[found].name, inode.tag,
+                    MIN(sizeof(sn_tab[found].name), sizeof(inode.tag)));
+            found++;
+        }
+    }
+
+    closesocket(fd);
+out:
+    *psn_tab = sn_tab;
+
+    qemu_free(vdi_inuse);
+
+    return found;
+}
+
+static int do_load_save_vmstate(BDRVSheepdogState *s, uint8_t *data,
+                                int64_t pos, int size, int load)
+{
+    int fd, create;
+    int ret = 0;
+    unsigned int data_len;
+    uint64_t vmstate_oid;
+    uint32_t vdi_index;
+    uint64_t offset;
+
+    fd = connect_to_sdog(s->addr, s->port);
+    if (fd < 0) {
+        ret = -EIO;
+        goto cleanup;
+    }
+
+    while (size) {
+        vdi_index = pos / SD_DATA_OBJ_SIZE;
+        offset = pos % SD_DATA_OBJ_SIZE;
+
+        data_len = MIN(size, SD_DATA_OBJ_SIZE);
+
+        vmstate_oid = vid_to_vmstate_oid(s->inode.vdi_id, vdi_index);
+
+        create = (offset == 0);
+        if (load) {
+            ret = read_object(fd, (char *)data, vmstate_oid,
+                              s->inode.nr_copies, data_len, offset);
+        } else {
+            ret = write_object(fd, (char *)data, vmstate_oid,
+                               s->inode.nr_copies, data_len, offset, create);
+        }
+
+        if (ret < 0) {
+            error_report("failed to save vmstate %s\n", strerror(errno));
+            ret = -EIO;
+            goto cleanup;
+        }
+
+        pos += data_len;
+        size -= data_len;
+        ret += data_len;
+    }
+cleanup:
+    closesocket(fd);
+    return ret;
+}
+
+static int sd_save_vmstate(BlockDriverState *bs, const uint8_t *data,
+                           int64_t pos, int size)
+{
+    BDRVSheepdogState *s = bs->opaque;
+
+    return do_load_save_vmstate(s, (uint8_t *)data, pos, size, 0);
+}
+
+static int sd_load_vmstate(BlockDriverState *bs, uint8_t *data,
+                           int64_t pos, int size)
+{
+    BDRVSheepdogState *s = bs->opaque;
+
+    return do_load_save_vmstate(s, data, pos, size, 1);
+}
+
+
+static QEMUOptionParameter sd_create_options[] = {
+    {
+        .name = BLOCK_OPT_SIZE,
+        .type = OPT_SIZE,
+        .help = "Virtual disk size"
+    },
+    {
+        .name = BLOCK_OPT_BACKING_FILE,
+        .type = OPT_STRING,
+        .help = "File name of a base image"
+    },
+    { NULL }
+};
+
+BlockDriver bdrv_sheepdog = {
+    .format_name    = "sheepdog",
+    .protocol_name  = "sheepdog",
+    .instance_size  = sizeof(BDRVSheepdogState),
+    .bdrv_file_open = sd_open,
+    .bdrv_close     = sd_close,
+    .bdrv_create    = sd_create,
+    .bdrv_getlength = sd_getlength,
+    .bdrv_truncate  = sd_truncate,
+
+    .bdrv_aio_readv     = sd_aio_readv,
+    .bdrv_aio_writev    = sd_aio_writev,
+
+    .bdrv_snapshot_create   = sd_snapshot_create,
+    .bdrv_snapshot_goto     = sd_snapshot_goto,
+    .bdrv_snapshot_delete   = sd_snapshot_delete,
+    .bdrv_snapshot_list     = sd_snapshot_list,
+
+    .bdrv_save_vmstate  = sd_save_vmstate,
+    .bdrv_load_vmstate  = sd_load_vmstate,
+
+    .create_options = sd_create_options,
+};
+
+static void bdrv_sheepdog_init(void)
+{
+    bdrv_register(&bdrv_sheepdog);
+}
+block_init(bdrv_sheepdog_init);