qemu/hw/9pfs/9p-proxy.c

/*
 * 9p Proxy callback
 *
 * Copyright IBM, Corp. 2011
 *
 * Authors:
 * M. Mohan Kumar <mohan@in.ibm.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 */

/*
 * Not so fast! You might want to read the 9p developer docs first:
 * https://wiki.qemu.org/Documentation/9p
 */

/*
 * NOTE: The 9p 'proxy' backend is deprecated (since QEMU 8.1) and will be
 * removed in a future version of QEMU!
 */

#include "qemu/osdep.h"
#include <sys/socket.h>
#include <sys/un.h>
#include "9p.h"
#include "qapi/error.h"
#include "qemu/cutils.h"
#include "qemu/error-report.h"
#include "qemu/option.h"
#include "fsdev/qemu-fsdev.h"
#include "9p-proxy.h"

typedef struct V9fsProxy {
    int sockfd;
    QemuMutex mutex;
    struct iovec in_iovec;
    struct iovec out_iovec;
} V9fsProxy;

/*
 * Return received file descriptor on success in *status.
 * errno is also returned on *status (which will be < 0)
 * return < 0 on transport error.
 */
static int v9fs_receivefd(int sockfd, int *status)
{
    struct iovec iov;
    struct msghdr msg;
    struct cmsghdr *cmsg;
    int retval, data, fd;
    union MsgControl msg_control;

    iov.iov_base = &data;
    iov.iov_len = sizeof(data);

    memset(&msg, 0, sizeof(msg));
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
    msg.msg_control = &msg_control;
    msg.msg_controllen = sizeof(msg_control);

    do {
        retval = recvmsg(sockfd, &msg, 0);
    } while (retval < 0 && errno == EINTR);
    if (retval <= 0) {
        return retval;
    }
    /*
     * data is set to V9FS_FD_VALID, if ancillary data is sent.  If this
     * request doesn't need ancillary data (fd) or an error occurred,
     * data is set to negative errno value.
     */
    if (data != V9FS_FD_VALID) {
        *status = data;
        return 0;
    }
    /*
     * File descriptor (fd) is sent in the ancillary data. Check if we
     * indeed received it. One of the reasons to fail to receive it is if
     * we exceeded the maximum number of file descriptors!
     */
    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
        if (cmsg->cmsg_len != CMSG_LEN(sizeof(int)) ||
            cmsg->cmsg_level != SOL_SOCKET ||
            cmsg->cmsg_type != SCM_RIGHTS) {
            continue;
        }
        fd = *((int *)CMSG_DATA(cmsg));
        *status = fd;
        return 0;
    }
    *status = -ENFILE;  /* Ancillary data sent but not received */
    return 0;
}

static ssize_t socket_read(int sockfd, void *buff, size_t size)
{
    ssize_t retval, total = 0;

    while (size) {
        retval = read(sockfd, buff, size);
        if (retval == 0) {
            return -EIO;
        }
        if (retval < 0) {
            if (errno == EINTR) {
                continue;
            }
            return -errno;
        }
        size -= retval;
        buff += retval;
        total += retval;
    }
    return total;
}

/* Converts proxy_statfs to VFS statfs structure */
static void prstatfs_to_statfs(struct statfs *stfs, ProxyStatFS *prstfs)
{
    memset(stfs, 0, sizeof(*stfs));
    stfs->f_type = prstfs->f_type;
    stfs->f_bsize = prstfs->f_bsize;
    stfs->f_blocks = prstfs->f_blocks;
    stfs->f_bfree = prstfs->f_bfree;
    stfs->f_bavail = prstfs->f_bavail;
    stfs->f_files = prstfs->f_files;
    stfs->f_ffree = prstfs->f_ffree;
#ifdef CONFIG_DARWIN
    /* f_namelen and f_frsize do not exist on Darwin */
    stfs->f_fsid.val[0] = prstfs->f_fsid[0] & 0xFFFFFFFFU;
    stfs->f_fsid.val[1] = prstfs->f_fsid[1] >> 32 & 0xFFFFFFFFU;
#else
    stfs->f_fsid.__val[0] = prstfs->f_fsid[0] & 0xFFFFFFFFU;
    stfs->f_fsid.__val[1] = prstfs->f_fsid[1] >> 32 & 0xFFFFFFFFU;
    stfs->f_namelen = prstfs->f_namelen;
    stfs->f_frsize = prstfs->f_frsize;
#endif
}

/* Converts proxy_stat structure to VFS stat structure */
static void prstat_to_stat(struct stat *stbuf, ProxyStat *prstat)
{
   memset(stbuf, 0, sizeof(*stbuf));
   stbuf->st_dev = prstat->st_dev;
   stbuf->st_ino = prstat->st_ino;
   stbuf->st_nlink = prstat->st_nlink;
   stbuf->st_mode = prstat->st_mode;
   stbuf->st_uid = prstat->st_uid;
   stbuf->st_gid = prstat->st_gid;
   stbuf->st_rdev = prstat->st_rdev;
   stbuf->st_size = prstat->st_size;
   stbuf->st_blksize = prstat->st_blksize;
   stbuf->st_blocks = prstat->st_blocks;
   stbuf->st_atime = prstat->st_atim_sec;
   stbuf->st_mtime = prstat->st_mtim_sec;
   stbuf->st_ctime = prstat->st_ctim_sec;
#ifdef CONFIG_DARWIN
   stbuf->st_atimespec.tv_sec = prstat->st_atim_sec;
   stbuf->st_mtimespec.tv_sec = prstat->st_mtim_sec;
   stbuf->st_ctimespec.tv_sec = prstat->st_ctim_sec;
   stbuf->st_atimespec.tv_nsec = prstat->st_atim_nsec;
   stbuf->st_mtimespec.tv_nsec = prstat->st_mtim_nsec;
   stbuf->st_ctimespec.tv_nsec = prstat->st_ctim_nsec;
#else
   stbuf->st_atim.tv_sec = prstat->st_atim_sec;
   stbuf->st_mtim.tv_sec = prstat->st_mtim_sec;
   stbuf->st_ctim.tv_sec = prstat->st_ctim_sec;
   stbuf->st_atim.tv_nsec = prstat->st_atim_nsec;
   stbuf->st_mtim.tv_nsec = prstat->st_mtim_nsec;
   stbuf->st_ctim.tv_nsec = prstat->st_ctim_nsec;
#endif
}

/*
 * Response contains two parts
 * {header, data}
 * header.type == T_ERROR, data -> -errno
 * header.type == T_SUCCESS, data -> response
 * size of errno/response is given by header.size
 * returns < 0, on transport error. response is
 * valid only if status >= 0.
 */
static int v9fs_receive_response(V9fsProxy *proxy, int type,
                                 int *status, void *response)
{
    int retval;
    ProxyHeader header;
    struct iovec *reply = &proxy->in_iovec;

    *status = 0;
    reply->iov_len = 0;
    retval = socket_read(proxy->sockfd, reply->iov_base, PROXY_HDR_SZ);
    if (retval < 0) {
        return retval;
    }
    reply->iov_len = PROXY_HDR_SZ;
    retval = proxy_unmarshal(reply, 0, "dd", &header.type, &header.size);
    assert(retval == 4 * 2);
    /*
     * if response size > PROXY_MAX_IO_SZ, read the response but ignore it and
     * return -ENOBUFS
     */
    if (header.size > PROXY_MAX_IO_SZ) {
        int count;
        while (header.size > 0) {
            count = MIN(PROXY_MAX_IO_SZ, header.size);
            count = socket_read(proxy->sockfd, reply->iov_base, count);
            if (count < 0) {
                return count;
            }
            header.size -= count;
        }
        *status = -ENOBUFS;
        return 0;
    }

    retval = socket_read(proxy->sockfd,
                         reply->iov_base + PROXY_HDR_SZ, header.size);
    if (retval < 0) {
        return retval;
    }
    reply->iov_len += header.size;
    /* there was an error during processing request */
    if (header.type == T_ERROR) {
        int ret;
        ret = proxy_unmarshal(reply, PROXY_HDR_SZ, "d", status);
        assert(ret == 4);
        return 0;
    }

    switch (type) {
    case T_LSTAT: {
        ProxyStat prstat;
        retval = proxy_unmarshal(reply, PROXY_HDR_SZ,
                                 "qqqdddqqqqqqqqqq", &prstat.st_dev,
                                 &prstat.st_ino, &prstat.st_nlink,
                                 &prstat.st_mode, &prstat.st_uid,
                                 &prstat.st_gid, &prstat.st_rdev,
                                 &prstat.st_size, &prstat.st_blksize,
                                 &prstat.st_blocks,
                                 &prstat.st_atim_sec, &prstat.st_atim_nsec,
                                 &prstat.st_mtim_sec, &prstat.st_mtim_nsec,
                                 &prstat.st_ctim_sec, &prstat.st_ctim_nsec);
        assert(retval == 8 * 3 + 4 * 3 + 8 * 10);
        prstat_to_stat(response, &prstat);
        break;
    }
    case T_STATFS: {
        ProxyStatFS prstfs;
        retval = proxy_unmarshal(reply, PROXY_HDR_SZ,
                                 "qqqqqqqqqqq", &prstfs.f_type,
                                 &prstfs.f_bsize, &prstfs.f_blocks,
                                 &prstfs.f_bfree, &prstfs.f_bavail,
                                 &prstfs.f_files, &prstfs.f_ffree,
                                 &prstfs.f_fsid[0], &prstfs.f_fsid[1],
                                 &prstfs.f_namelen, &prstfs.f_frsize);
        assert(retval == 8 * 11);
        prstatfs_to_statfs(response, &prstfs);
        break;
    }
    case T_READLINK: {
        V9fsString target;
        v9fs_string_init(&target);
        retval = proxy_unmarshal(reply, PROXY_HDR_SZ, "s", &target);
        strcpy(response, target.data);
        v9fs_string_free(&target);
        break;
    }
    case T_LGETXATTR:
    case T_LLISTXATTR: {
        V9fsString xattr;
        v9fs_string_init(&xattr);
        retval = proxy_unmarshal(reply, PROXY_HDR_SZ, "s", &xattr);
        memcpy(response, xattr.data, xattr.size);
        v9fs_string_free(&xattr);
        break;
    }
    case T_GETVERSION:
        retval = proxy_unmarshal(reply, PROXY_HDR_SZ, "q", response);
        assert(retval == 8);
        break;
    default:
        return -1;
    }
    if (retval < 0) {
        *status  = retval;
    }
    return 0;
}

/*
 * return < 0 on transport error.
 * *status is valid only if return >= 0
 */
static int v9fs_receive_status(V9fsProxy *proxy,
                               struct iovec *reply, int *status)
{
    int retval;
    ProxyHeader header;

    *status = 0;
    reply->iov_len = 0;
    retval = socket_read(proxy->sockfd, reply->iov_base, PROXY_HDR_SZ);
    if (retval < 0) {
        return retval;
    }
    reply->iov_len = PROXY_HDR_SZ;
    retval = proxy_unmarshal(reply, 0, "dd", &header.type, &header.size);
    assert(retval == 4 * 2);
    retval = socket_read(proxy->sockfd,
                         reply->iov_base + PROXY_HDR_SZ, header.size);
    if (retval < 0) {
        return retval;
    }
    reply->iov_len += header.size;
    retval = proxy_unmarshal(reply, PROXY_HDR_SZ, "d", status);
    assert(retval == 4);
    return 0;
}

/*
 * Proxy->header and proxy->request written to socket by QEMU process.
 * This request read by proxy helper process
 * returns 0 on success and -errno on error
 */
static int v9fs_request(V9fsProxy *proxy, int type, void *response, ...)
{
    dev_t rdev;
    va_list ap;
    int size = 0;
    int retval = 0;
    uint64_t offset;
    ProxyHeader header = { 0, 0};
    struct timespec spec[2];
    int flags, mode, uid, gid;
    V9fsString *name, *value;
    V9fsString *path, *oldpath;
    struct iovec *iovec = NULL, *reply = NULL;

    qemu_mutex_lock(&proxy->mutex);

    if (proxy->sockfd == -1) {
        retval = -EIO;
        goto err_out;
    }
    iovec = &proxy->out_iovec;
    reply = &proxy->in_iovec;
    va_start(ap, response);
    switch (type) {
    case T_OPEN:
        path = va_arg(ap, V9fsString *);
        flags = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "sd", path, flags);
        if (retval > 0) {
            header.size = retval;
            header.type = T_OPEN;
        }
        break;
    case T_CREATE:
        path = va_arg(ap, V9fsString *);
        flags = va_arg(ap, int);
        mode = va_arg(ap, int);
        uid = va_arg(ap, int);
        gid = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "sdddd", path,
                                    flags, mode, uid, gid);
        if (retval > 0) {
            header.size = retval;
            header.type = T_CREATE;
        }
        break;
    case T_MKNOD:
        path = va_arg(ap, V9fsString *);
        mode = va_arg(ap, int);
        rdev = va_arg(ap, long int);
        uid = va_arg(ap, int);
        gid = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "ddsdq",
                                    uid, gid, path, mode, rdev);
        if (retval > 0) {
            header.size = retval;
            header.type = T_MKNOD;
        }
        break;
    case T_MKDIR:
        path = va_arg(ap, V9fsString *);
        mode = va_arg(ap, int);
        uid = va_arg(ap, int);
        gid = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "ddsd",
                                    uid, gid, path, mode);
        if (retval > 0) {
            header.size = retval;
            header.type = T_MKDIR;
        }
        break;
    case T_SYMLINK:
        oldpath = va_arg(ap, V9fsString *);
        path = va_arg(ap, V9fsString *);
        uid = va_arg(ap, int);
        gid = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "ddss",
                                    uid, gid, oldpath, path);
        if (retval > 0) {
            header.size = retval;
            header.type = T_SYMLINK;
        }
        break;
    case T_LINK:
        oldpath = va_arg(ap, V9fsString *);
        path = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "ss",
                                    oldpath, path);
        if (retval > 0) {
            header.size = retval;
            header.type = T_LINK;
        }
        break;
    case T_LSTAT:
        path = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "s", path);
        if (retval > 0) {
            header.size = retval;
            header.type = T_LSTAT;
        }
        break;
    case T_READLINK:
        path = va_arg(ap, V9fsString *);
        size = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "sd", path, size);
        if (retval > 0) {
            header.size = retval;
            header.type = T_READLINK;
        }
        break;
    case T_STATFS:
        path = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "s", path);
        if (retval > 0) {
            header.size = retval;
            header.type = T_STATFS;
        }
        break;
    case T_CHMOD:
        path = va_arg(ap, V9fsString *);
        mode = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "sd", path, mode);
        if (retval > 0) {
            header.size = retval;
            header.type = T_CHMOD;
        }
        break;
    case T_CHOWN:
        path = va_arg(ap, V9fsString *);
        uid = va_arg(ap, int);
        gid = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "sdd", path, uid, gid);
        if (retval > 0) {
            header.size = retval;
            header.type = T_CHOWN;
        }
        break;
    case T_TRUNCATE:
        path = va_arg(ap, V9fsString *);
        offset = va_arg(ap, uint64_t);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "sq", path, offset);
        if (retval > 0) {
            header.size = retval;
            header.type = T_TRUNCATE;
        }
        break;
    case T_UTIME:
        path = va_arg(ap, V9fsString *);
        spec[0].tv_sec = va_arg(ap, long);
        spec[0].tv_nsec = va_arg(ap, long);
        spec[1].tv_sec = va_arg(ap, long);
        spec[1].tv_nsec = va_arg(ap, long);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "sqqqq", path,
                                    spec[0].tv_sec, spec[1].tv_nsec,
                                    spec[1].tv_sec, spec[1].tv_nsec);
        if (retval > 0) {
            header.size = retval;
            header.type = T_UTIME;
        }
        break;
    case T_RENAME:
        oldpath = va_arg(ap, V9fsString *);
        path = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "ss", oldpath, path);
        if (retval > 0) {
            header.size = retval;
            header.type = T_RENAME;
        }
        break;
    case T_REMOVE:
        path = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "s", path);
        if (retval > 0) {
            header.size = retval;
            header.type = T_REMOVE;
        }
        break;
    case T_LGETXATTR:
        size = va_arg(ap, int);
        path = va_arg(ap, V9fsString *);
        name = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ,
                                    "dss", size, path, name);
        if (retval > 0) {
            header.size = retval;
            header.type = T_LGETXATTR;
        }
        break;
    case T_LLISTXATTR:
        size = va_arg(ap, int);
        path = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "ds", size, path);
        if (retval > 0) {
            header.size = retval;
            header.type = T_LLISTXATTR;
        }
        break;
    case T_LSETXATTR:
        path = va_arg(ap, V9fsString *);
        name = va_arg(ap, V9fsString *);
        value = va_arg(ap, V9fsString *);
        size = va_arg(ap, int);
        flags = va_arg(ap, int);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "sssdd",
                                    path, name, value, size, flags);
        if (retval > 0) {
            header.size = retval;
            header.type = T_LSETXATTR;
        }
        break;
    case T_LREMOVEXATTR:
        path = va_arg(ap, V9fsString *);
        name = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "ss", path, name);
        if (retval > 0) {
            header.size = retval;
            header.type = T_LREMOVEXATTR;
        }
        break;
    case T_GETVERSION:
        path = va_arg(ap, V9fsString *);
        retval = proxy_marshal(iovec, PROXY_HDR_SZ, "s", path);
        if (retval > 0) {
            header.size = retval;
            header.type = T_GETVERSION;
        }
        break;
    default:
        error_report("Invalid type %d", type);
        retval = -EINVAL;
        break;
    }
    va_end(ap);

    if (retval < 0) {
        goto err_out;
    }

    /* marshal the header details */
    retval = proxy_marshal(iovec, 0, "dd", header.type, header.size);
    assert(retval == 4 * 2);
    header.size += PROXY_HDR_SZ;

    retval = qemu_write_full(proxy->sockfd, iovec->iov_base, header.size);
    if (retval != header.size) {
        goto close_error;
    }

    switch (type) {
    case T_OPEN:
    case T_CREATE:
        /*
         * A file descriptor is returned as response for
         * T_OPEN,T_CREATE on success
         */
        if (v9fs_receivefd(proxy->sockfd, &retval) < 0) {
            goto close_error;
        }
        break;
    case T_MKNOD:
    case T_MKDIR:
    case T_SYMLINK:
    case T_LINK:
    case T_CHMOD:
    case T_CHOWN:
    case T_RENAME:
    case T_TRUNCATE:
    case T_UTIME:
    case T_REMOVE:
    case T_LSETXATTR:
    case T_LREMOVEXATTR:
        if (v9fs_receive_status(proxy, reply, &retval) < 0) {
            goto close_error;
        }
        break;
    case T_LSTAT:
    case T_READLINK:
    case T_STATFS:
    case T_GETVERSION:
        if (v9fs_receive_response(proxy, type, &retval, response) < 0) {
            goto close_error;
        }
        break;
    case T_LGETXATTR:
    case T_LLISTXATTR:
        if (!size) {
            if (v9fs_receive_status(proxy, reply, &retval) < 0) {
                goto close_error;
            }
        } else {
            if (v9fs_receive_response(proxy, type, &retval, response) < 0) {
                goto close_error;
            }
        }
        break;
    }

err_out:
    qemu_mutex_unlock(&proxy->mutex);
    return retval;

close_error:
    close(proxy->sockfd);
    proxy->sockfd = -1;
    qemu_mutex_unlock(&proxy->mutex);
    return -EIO;
}

static int proxy_lstat(FsContext *fs_ctx, V9fsPath *fs_path, struct stat *stbuf)
{
    int retval;
    retval = v9fs_request(fs_ctx->private, T_LSTAT, stbuf, fs_path);
    if (retval < 0) {
        errno = -retval;
        return -1;
    }
    return retval;
}

static ssize_t proxy_readlink(FsContext *fs_ctx, V9fsPath *fs_path,
                              char *buf, size_t bufsz)
{
    int retval;
    retval = v9fs_request(fs_ctx->private, T_READLINK, buf, fs_path, bufsz);
    if (retval < 0) {
        errno = -retval;
        return -1;
    }
    return strlen(buf);
}

static int proxy_close(FsContext *ctx, V9fsFidOpenState *fs)
{
    return close(fs->fd);
}

static int proxy_closedir(FsContext *ctx, V9fsFidOpenState *fs)
{
    return closedir(fs->dir.stream);
}

static int proxy_open(FsContext *ctx, V9fsPath *fs_path,
                      int flags, V9fsFidOpenState *fs)
{
    fs->fd = v9fs_request(ctx->private, T_OPEN, NULL, fs_path, flags);
    if (fs->fd < 0) {
        errno = -fs->fd;
        fs->fd = -1;
    }
    return fs->fd;
}

static int proxy_opendir(FsContext *ctx,
                         V9fsPath *fs_path, V9fsFidOpenState *fs)
{
    int serrno, fd;

    fs->dir.stream = NULL;
    fd = v9fs_request(ctx->private, T_OPEN, NULL, fs_path, O_DIRECTORY);
    if (fd < 0) {
        errno = -fd;
        return -1;
    }
    fs->dir.stream = fdopendir(fd);
    if (!fs->dir.stream) {
        serrno = errno;
        close(fd);
        errno = serrno;
        return -1;
    }
    return 0;
}

static void proxy_rewinddir(FsContext *ctx, V9fsFidOpenState *fs)
{
    rewinddir(fs->dir.stream);
}

static off_t proxy_telldir(FsContext *ctx, V9fsFidOpenState *fs)
{
    return telldir(fs->dir.stream);
}

static struct dirent *proxy_readdir(FsContext *ctx, V9fsFidOpenState *fs)
{
    struct dirent *entry;
    entry = readdir(fs->dir.stream);
#ifdef CONFIG_DARWIN
    if (!entry) {
        return NULL;
    }
    int td;
    td = telldir(fs->dir.stream);
    /* If telldir fails, fail the entire readdir call */
    if (td < 0) {
        return NULL;
    }
    entry->d_seekoff = td;
#endif
    return entry;
}

static void proxy_seekdir(FsContext *ctx, V9fsFidOpenState *fs, off_t off)
{
    seekdir(fs->dir.stream, off);
}

static ssize_t proxy_preadv(FsContext *ctx, V9fsFidOpenState *fs,
                            const struct iovec *iov,
                            int iovcnt, off_t offset)
{
    ssize_t ret;
#ifdef CONFIG_PREADV
    ret = preadv(fs->fd, iov, iovcnt, offset);
#else
    ret = lseek(fs->fd, offset, SEEK_SET);
    if (ret >= 0) {
        ret = readv(fs->fd, iov, iovcnt);
    }
#endif
    return ret;
}

static ssize_t proxy_pwritev(FsContext *ctx, V9fsFidOpenState *fs,
                             const struct iovec *iov,
                             int iovcnt, off_t offset)
{
    ssize_t ret;

#ifdef CONFIG_PREADV
    ret = pwritev(fs->fd, iov, iovcnt, offset);
#else
    ret = lseek(fs->fd, offset, SEEK_SET);
    if (ret >= 0) {
        ret = writev(fs->fd, iov, iovcnt);
    }
#endif
#ifdef CONFIG_SYNC_FILE_RANGE
    if (ret > 0 && ctx->export_flags & V9FS_IMMEDIATE_WRITEOUT) {
        /*
         * Initiate a writeback. This is not a data integrity sync.
         * We want to ensure that we don't leave dirty pages in the cache
         * after write when writeout=immediate is specified.
         */
        sync_file_range(fs->fd, offset, ret,
                        SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE);
    }
#endif
    return ret;
}

static int proxy_chmod(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)
{
    int retval;
    retval = v9fs_request(fs_ctx->private, T_CHMOD, NULL, fs_path,
                          credp->fc_mode);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static int proxy_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
                       const char *name, FsCred *credp)
{
    int retval;
    V9fsString fullname;

    v9fs_string_init(&fullname);
    v9fs_string_sprintf(&fullname, "%s/%s", dir_path->data, name);

    retval = v9fs_request(fs_ctx->private, T_MKNOD, NULL, &fullname,
                          credp->fc_mode, credp->fc_rdev,
                          credp->fc_uid, credp->fc_gid);
    v9fs_string_free(&fullname);
    if (retval < 0) {
        errno = -retval;
        retval = -1;
    }
    return retval;
}

static int proxy_mkdir(FsContext *fs_ctx, V9fsPath *dir_path,
                       const char *name, FsCred *credp)
{
    int retval;
    V9fsString fullname;

    v9fs_string_init(&fullname);
    v9fs_string_sprintf(&fullname, "%s/%s", dir_path->data, name);

    retval = v9fs_request(fs_ctx->private, T_MKDIR, NULL, &fullname,
                          credp->fc_mode, credp->fc_uid, credp->fc_gid);
    v9fs_string_free(&fullname);
    if (retval < 0) {
        errno = -retval;
        retval = -1;
    }
    return retval;
}

static int proxy_fstat(FsContext *fs_ctx, int fid_type,
                       V9fsFidOpenState *fs, struct stat *stbuf)
{
    int fd;

    if (fid_type == P9_FID_DIR) {
        fd = dirfd(fs->dir.stream);
    } else {
        fd = fs->fd;
    }
    return fstat(fd, stbuf);
}

static int proxy_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name,
                       int flags, FsCred *credp, V9fsFidOpenState *fs)
{
    V9fsString fullname;

    v9fs_string_init(&fullname);
    v9fs_string_sprintf(&fullname, "%s/%s", dir_path->data, name);

    fs->fd = v9fs_request(fs_ctx->private, T_CREATE, NULL, &fullname, flags,
                          credp->fc_mode, credp->fc_uid, credp->fc_gid);
    v9fs_string_free(&fullname);
    if (fs->fd < 0) {
        errno = -fs->fd;
        fs->fd = -1;
    }
    return fs->fd;
}

static int proxy_symlink(FsContext *fs_ctx, const char *oldpath,
                         V9fsPath *dir_path, const char *name, FsCred *credp)
{
    int retval;
    V9fsString fullname, target;

    v9fs_string_init(&fullname);
    v9fs_string_init(&target);

    v9fs_string_sprintf(&fullname, "%s/%s", dir_path->data, name);
    v9fs_string_sprintf(&target, "%s", oldpath);

    retval = v9fs_request(fs_ctx->private, T_SYMLINK, NULL, &target, &fullname,
                          credp->fc_uid, credp->fc_gid);
    v9fs_string_free(&fullname);
    v9fs_string_free(&target);
    if (retval < 0) {
        errno = -retval;
        retval = -1;
    }
    return retval;
}

static int proxy_link(FsContext *ctx, V9fsPath *oldpath,
                      V9fsPath *dirpath, const char *name)
{
    int retval;
    V9fsString newpath;

    v9fs_string_init(&newpath);
    v9fs_string_sprintf(&newpath, "%s/%s", dirpath->data, name);

    retval = v9fs_request(ctx->private, T_LINK, NULL, oldpath, &newpath);
    v9fs_string_free(&newpath);
    if (retval < 0) {
        errno = -retval;
        retval = -1;
    }
    return retval;
}

static int proxy_truncate(FsContext *ctx, V9fsPath *fs_path, off_t size)
{
    int retval;

    retval = v9fs_request(ctx->private, T_TRUNCATE, NULL, fs_path, size);
    if (retval < 0) {
        errno = -retval;
        return -1;
    }
    return 0;
}

static int proxy_rename(FsContext *ctx, const char *oldpath,
                        const char *newpath)
{
    int retval;
    V9fsString oldname, newname;

    v9fs_string_init(&oldname);
    v9fs_string_init(&newname);

    v9fs_string_sprintf(&oldname, "%s", oldpath);
    v9fs_string_sprintf(&newname, "%s", newpath);
    retval = v9fs_request(ctx->private, T_RENAME, NULL, &oldname, &newname);
    v9fs_string_free(&oldname);
    v9fs_string_free(&newname);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static int proxy_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)
{
    int retval;
    retval = v9fs_request(fs_ctx->private, T_CHOWN, NULL, fs_path,
                          credp->fc_uid, credp->fc_gid);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static int proxy_utimensat(FsContext *s, V9fsPath *fs_path,
                           const struct timespec *buf)
{
    int retval;
    retval = v9fs_request(s->private, T_UTIME, NULL, fs_path,
                          buf[0].tv_sec, buf[0].tv_nsec,
                          buf[1].tv_sec, buf[1].tv_nsec);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static int proxy_remove(FsContext *ctx, const char *path)
{
    int retval;
    V9fsString name;
    v9fs_string_init(&name);
    v9fs_string_sprintf(&name, "%s", path);
    retval = v9fs_request(ctx->private, T_REMOVE, NULL, &name);
    v9fs_string_free(&name);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static int proxy_fsync(FsContext *ctx, int fid_type,
                       V9fsFidOpenState *fs, int datasync)
{
    int fd;

    if (fid_type == P9_FID_DIR) {
        fd = dirfd(fs->dir.stream);
    } else {
        fd = fs->fd;
    }

    if (datasync) {
        return qemu_fdatasync(fd);
    } else {
        return fsync(fd);
    }
}

static int proxy_statfs(FsContext *s, V9fsPath *fs_path, struct statfs *stbuf)
{
    int retval;
    retval = v9fs_request(s->private, T_STATFS, stbuf, fs_path);
    if (retval < 0) {
        errno = -retval;
        return -1;
    }
    return retval;
}

static ssize_t proxy_lgetxattr(FsContext *ctx, V9fsPath *fs_path,
                               const char *name, void *value, size_t size)
{
    int retval;
    V9fsString xname;

    v9fs_string_init(&xname);
    v9fs_string_sprintf(&xname, "%s", name);
    retval = v9fs_request(ctx->private, T_LGETXATTR, value, size, fs_path,
                          &xname);
    v9fs_string_free(&xname);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static ssize_t proxy_llistxattr(FsContext *ctx, V9fsPath *fs_path,
                                void *value, size_t size)
{
    int retval;
    retval = v9fs_request(ctx->private, T_LLISTXATTR, value, size, fs_path);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static int proxy_lsetxattr(FsContext *ctx, V9fsPath *fs_path, const char *name,
                           void *value, size_t size, int flags)
{
    int retval;
    V9fsString xname, xvalue;

    v9fs_string_init(&xname);
    v9fs_string_sprintf(&xname, "%s", name);

    v9fs_string_init(&xvalue);
    xvalue.size = size;
    xvalue.data = g_malloc(size);
    memcpy(xvalue.data, value, size);

    retval = v9fs_request(ctx->private, T_LSETXATTR, value, fs_path, &xname,
                          &xvalue, size, flags);
    v9fs_string_free(&xname);
    v9fs_string_free(&xvalue);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static int proxy_lremovexattr(FsContext *ctx, V9fsPath *fs_path,
                              const char *name)
{
    int retval;
    V9fsString xname;

    v9fs_string_init(&xname);
    v9fs_string_sprintf(&xname, "%s", name);
    retval = v9fs_request(ctx->private, T_LREMOVEXATTR, NULL, fs_path, &xname);
    v9fs_string_free(&xname);
    if (retval < 0) {
        errno = -retval;
    }
    return retval;
}

static int proxy_name_to_path(FsContext *ctx, V9fsPath *dir_path,
                              const char *name, V9fsPath *target)
{
    if (dir_path) {
        v9fs_path_sprintf(target, "%s/%s", dir_path->data, name);
    } else {
        v9fs_path_sprintf(target, "%s", name);
    }
    return 0;
}

static int proxy_renameat(FsContext *ctx, V9fsPath *olddir,
                          const char *old_name, V9fsPath *newdir,
                          const char *new_name)
{
    int ret;
    V9fsString old_full_name, new_full_name;

    v9fs_string_init(&old_full_name);
    v9fs_string_init(&new_full_name);

    v9fs_string_sprintf(&old_full_name, "%s/%s", olddir->data, old_name);
    v9fs_string_sprintf(&new_full_name, "%s/%s", newdir->data, new_name);

    ret = proxy_rename(ctx, old_full_name.data, new_full_name.data);
    v9fs_string_free(&old_full_name);
    v9fs_string_free(&new_full_name);
    return ret;
}

static int proxy_unlinkat(FsContext *ctx, V9fsPath *dir,
                          const char *name, int flags)
{
    int ret;
    V9fsString fullname;
    v9fs_string_init(&fullname);

    v9fs_string_sprintf(&fullname, "%s/%s", dir->data, name);
    ret = proxy_remove(ctx, fullname.data);
    v9fs_string_free(&fullname);

    return ret;
}

static int proxy_ioc_getversion(FsContext *fs_ctx, V9fsPath *path,
                                mode_t st_mode, uint64_t *st_gen)
{
    int err;

    /* Do not try to open special files like device nodes, fifos etc
     * we can get fd for regular files and directories only
     */
    if (!S_ISREG(st_mode) && !S_ISDIR(st_mode)) {
        errno = ENOTTY;
        return -1;
    }
    err = v9fs_request(fs_ctx->private, T_GETVERSION, st_gen, path);
    if (err < 0) {
        errno = -err;
        err = -1;
    }
    return err;
}

static int connect_namedsocket(const char *path, Error **errp)
{
    int sockfd;
    struct sockaddr_un helper;

    if (strlen(path) >= sizeof(helper.sun_path)) {
        error_setg(errp, "socket name too long");
        return -1;
    }
    sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sockfd < 0) {
        error_setg_errno(errp, errno, "failed to create client socket");
        return -1;
    }
    strcpy(helper.sun_path, path);
    helper.sun_family = AF_UNIX;
    if (connect(sockfd, (struct sockaddr *)&helper, sizeof(helper)) < 0) {
        error_setg_errno(errp, errno, "failed to connect to '%s'", path);
        close(sockfd);
        return -1;
    }

    /* remove the socket for security reasons */
    unlink(path);
    return sockfd;
}

static void error_append_socket_sockfd_hint(Error *const *errp)
{
    error_append_hint(errp, "Either specify socket=/some/path where /some/path"
                      " points to a listening AF_UNIX socket or sock_fd=fd"
                      " where fd is a file descriptor to a connected AF_UNIX"
                      " socket\n");
}

static int proxy_parse_opts(QemuOpts *opts, FsDriverEntry *fs, Error **errp)
{
    const char *socket = qemu_opt_get(opts, "socket");
    const char *sock_fd = qemu_opt_get(opts, "sock_fd");

    if (!socket && !sock_fd) {
        error_setg(errp, "both socket and sock_fd properties are missing");
        error_append_socket_sockfd_hint(errp);
        return -1;
    }
    if (socket && sock_fd) {
        error_setg(errp, "both socket and sock_fd properties are set");
        error_append_socket_sockfd_hint(errp);
        return -1;
    }
    if (socket) {
        fs->path = g_strdup(socket);
        fs->export_flags |= V9FS_PROXY_SOCK_NAME;
    } else {
        fs->path = g_strdup(sock_fd);
        fs->export_flags |= V9FS_PROXY_SOCK_FD;
    }
    return 0;
}

static int proxy_init(FsContext *ctx, Error **errp)
{
    V9fsProxy *proxy = g_new(V9fsProxy, 1);
    int sock_id;

    if (ctx->export_flags & V9FS_PROXY_SOCK_NAME) {
        sock_id = connect_namedsocket(ctx->fs_root, errp);
    } else {
        sock_id = atoi(ctx->fs_root);
        if (sock_id < 0) {
            error_setg(errp, "socket descriptor not initialized");
        }
    }
    if (sock_id < 0) {
        g_free(proxy);
        return -1;
    }
    g_free(ctx->fs_root);
    ctx->fs_root = NULL;

    proxy->in_iovec.iov_base  = g_malloc(PROXY_MAX_IO_SZ + PROXY_HDR_SZ);
    proxy->in_iovec.iov_len   = PROXY_MAX_IO_SZ + PROXY_HDR_SZ;
    proxy->out_iovec.iov_base = g_malloc(PROXY_MAX_IO_SZ + PROXY_HDR_SZ);
    proxy->out_iovec.iov_len  = PROXY_MAX_IO_SZ + PROXY_HDR_SZ;

    ctx->private = proxy;
    proxy->sockfd = sock_id;
    qemu_mutex_init(&proxy->mutex);

    ctx->export_flags |= V9FS_PATHNAME_FSCONTEXT;
    ctx->exops.get_st_gen = proxy_ioc_getversion;
    return 0;
}

static void proxy_cleanup(FsContext *ctx)
{
    V9fsProxy *proxy = ctx->private;

    if (!proxy) {
        return;
    }

    g_free(proxy->out_iovec.iov_base);
    g_free(proxy->in_iovec.iov_base);
    if (ctx->export_flags & V9FS_PROXY_SOCK_NAME) {
        close(proxy->sockfd);
    }
    g_free(proxy);
}

FileOperations proxy_ops = {
    .parse_opts   = proxy_parse_opts,
    .init         = proxy_init,
    .cleanup      = proxy_cleanup,
    .lstat        = proxy_lstat,
    .readlink     = proxy_readlink,
    .close        = proxy_close,
    .closedir     = proxy_closedir,
    .open         = proxy_open,
    .opendir      = proxy_opendir,
    .rewinddir    = proxy_rewinddir,
    .telldir      = proxy_telldir,
    .readdir      = proxy_readdir,
    .seekdir      = proxy_seekdir,
    .preadv       = proxy_preadv,
    .pwritev      = proxy_pwritev,
    .chmod        = proxy_chmod,
    .mknod        = proxy_mknod,
    .mkdir        = proxy_mkdir,
    .fstat        = proxy_fstat,
    .open2        = proxy_open2,
    .symlink      = proxy_symlink,
    .link         = proxy_link,
    .truncate     = proxy_truncate,
    .rename       = proxy_rename,
    .chown        = proxy_chown,
    .utimensat    = proxy_utimensat,
    .remove       = proxy_remove,
    .fsync        = proxy_fsync,
    .statfs       = proxy_statfs,
    .lgetxattr    = proxy_lgetxattr,
    .llistxattr   = proxy_llistxattr,
    .lsetxattr    = proxy_lsetxattr,
    .lremovexattr = proxy_lremovexattr,
    .name_to_path = proxy_name_to_path,
    .renameat     = proxy_renameat,
    .unlinkat     = proxy_unlinkat,
};