Archipelago » qemu

/*

 * Virtio 9p backend

 *

 * Copyright IBM, Corp. 2010

 *

 * Authors:

 *  Anthony Liguori   <aliguori@us.ibm.com>

 *

 * This work is licensed under the terms of the GNU GPL, version 2.  See

 * the COPYING file in the top-level directory.

 *

 */

#include "virtio.h"

#include "pc.h"

#include "qemu_socket.h"

#include "virtio-9p.h"

#include "fsdev/qemu-fsdev.h"

#include "virtio-9p-debug.h"

#include "virtio-9p-xattr.h"

int debug_9p_pdu;

enum {

    Oread   = 0x00,

    Owrite  = 0x01,

    Ordwr   = 0x02,

    Oexec   = 0x03,

    Oexcl   = 0x04,

    Otrunc  = 0x10,

    Orexec  = 0x20,

    Orclose = 0x40,

    Oappend = 0x80,

};

static int omode_to_uflags(int8_t mode)

{

    int ret = 0;

    switch (mode & 3) {

    case Oread:

        ret = O_RDONLY;

        break;

    case Ordwr:

        ret = O_RDWR;

        break;

    case Owrite:

        ret = O_WRONLY;

        break;

    case Oexec:

        ret = O_RDONLY;

        break;

    }

    if (mode & Otrunc) {

        ret |= O_TRUNC;

    }

    if (mode & Oappend) {

        ret |= O_APPEND;

    }

    if (mode & Oexcl) {

        ret |= O_EXCL;

    }

    return ret;

}

void cred_init(FsCred *credp)

{

    credp->fc_uid = -1;

    credp->fc_gid = -1;

    credp->fc_mode = -1;

    credp->fc_rdev = -1;

}

static int v9fs_do_lstat(V9fsState *s, V9fsString *path, struct stat *stbuf)

{

    return s->ops->lstat(&s->ctx, path->data, stbuf);

}

static ssize_t v9fs_do_readlink(V9fsState *s, V9fsString *path, V9fsString *buf)

{

    ssize_t len;

    buf->data = qemu_malloc(1024);

    len = s->ops->readlink(&s->ctx, path->data, buf->data, 1024 - 1);

    if (len > -1) {

        buf->size = len;

        buf->data[len] = 0;

    }

    return len;

}

static int v9fs_do_close(V9fsState *s, int fd)

{

    return s->ops->close(&s->ctx, fd);

}

static int v9fs_do_closedir(V9fsState *s, DIR *dir)

{

    return s->ops->closedir(&s->ctx, dir);

}

static int v9fs_do_open(V9fsState *s, V9fsString *path, int flags)

{

    return s->ops->open(&s->ctx, path->data, flags);

}

static DIR *v9fs_do_opendir(V9fsState *s, V9fsString *path)

{

    return s->ops->opendir(&s->ctx, path->data);

}

static void v9fs_do_rewinddir(V9fsState *s, DIR *dir)

{

    return s->ops->rewinddir(&s->ctx, dir);

}

static off_t v9fs_do_telldir(V9fsState *s, DIR *dir)

{

    return s->ops->telldir(&s->ctx, dir);

}

static struct dirent *v9fs_do_readdir(V9fsState *s, DIR *dir)

{

    return s->ops->readdir(&s->ctx, dir);

}

static void v9fs_do_seekdir(V9fsState *s, DIR *dir, off_t off)

{

    return s->ops->seekdir(&s->ctx, dir, off);

}

static int v9fs_do_readv(V9fsState *s, int fd, const struct iovec *iov,

                            int iovcnt)

{

    return s->ops->readv(&s->ctx, fd, iov, iovcnt);

}

static off_t v9fs_do_lseek(V9fsState *s, int fd, off_t offset, int whence)

{

    return s->ops->lseek(&s->ctx, fd, offset, whence);

}

static int v9fs_do_writev(V9fsState *s, int fd, const struct iovec *iov,

                       int iovcnt)

{

    return s->ops->writev(&s->ctx, fd, iov, iovcnt);

}

static int v9fs_do_chmod(V9fsState *s, V9fsString *path, mode_t mode)

{

    FsCred cred;

    cred_init(&cred);

    cred.fc_mode = mode;

    return s->ops->chmod(&s->ctx, path->data, &cred);

}

static int v9fs_do_mknod(V9fsState *s, char *name,

        mode_t mode, dev_t dev, uid_t uid, gid_t gid)

{

    FsCred cred;

    cred_init(&cred);

    cred.fc_uid = uid;

    cred.fc_gid = gid;

    cred.fc_mode = mode;

    cred.fc_rdev = dev;

    return s->ops->mknod(&s->ctx, name, &cred);

}

static int v9fs_do_mkdir(V9fsState *s, char *name, mode_t mode,

                uid_t uid, gid_t gid)

{

    FsCred cred;

    cred_init(&cred);

    cred.fc_uid = uid;

    cred.fc_gid = gid;

    cred.fc_mode = mode;

    return s->ops->mkdir(&s->ctx, name, &cred);

}

static int v9fs_do_fstat(V9fsState *s, int fd, struct stat *stbuf)

{

    return s->ops->fstat(&s->ctx, fd, stbuf);

}

static int v9fs_do_open2(V9fsState *s, char *fullname, uid_t uid, gid_t gid,

        int flags, int mode)

{

    FsCred cred;

    cred_init(&cred);

    cred.fc_uid = uid;

    cred.fc_gid = gid;

    cred.fc_mode = mode & 07777;

    flags = flags;

    return s->ops->open2(&s->ctx, fullname, flags, &cred);

}

static int v9fs_do_symlink(V9fsState *s, V9fsFidState *fidp,

        const char *oldpath, const char *newpath, gid_t gid)

{

    FsCred cred;

    cred_init(&cred);

    cred.fc_uid = fidp->uid;

    cred.fc_gid = gid;

    cred.fc_mode = 0777;

    return s->ops->symlink(&s->ctx, oldpath, newpath, &cred);

}

static int v9fs_do_link(V9fsState *s, V9fsString *oldpath, V9fsString *newpath)

{

    return s->ops->link(&s->ctx, oldpath->data, newpath->data);

}

static int v9fs_do_truncate(V9fsState *s, V9fsString *path, off_t size)

{

    return s->ops->truncate(&s->ctx, path->data, size);

}

static int v9fs_do_rename(V9fsState *s, V9fsString *oldpath,

                            V9fsString *newpath)

{

    return s->ops->rename(&s->ctx, oldpath->data, newpath->data);

}

static int v9fs_do_chown(V9fsState *s, V9fsString *path, uid_t uid, gid_t gid)

{

    FsCred cred;

    cred_init(&cred);

    cred.fc_uid = uid;

    cred.fc_gid = gid;

    return s->ops->chown(&s->ctx, path->data, &cred);

}

static int v9fs_do_utimensat(V9fsState *s, V9fsString *path,

                                           const struct timespec times[2])

{

    return s->ops->utimensat(&s->ctx, path->data, times);

}

static int v9fs_do_remove(V9fsState *s, V9fsString *path)

{

    return s->ops->remove(&s->ctx, path->data);

}

static int v9fs_do_fsync(V9fsState *s, int fd)

{

    return s->ops->fsync(&s->ctx, fd);

}

static int v9fs_do_statfs(V9fsState *s, V9fsString *path, struct statfs *stbuf)

{

    return s->ops->statfs(&s->ctx, path->data, stbuf);

}

static ssize_t v9fs_do_lgetxattr(V9fsState *s, V9fsString *path,

                             V9fsString *xattr_name,

                             void *value, size_t size)

{

    return s->ops->lgetxattr(&s->ctx, path->data,

                             xattr_name->data, value, size);

}

static ssize_t v9fs_do_llistxattr(V9fsState *s, V9fsString *path,

                              void *value, size_t size)

{

    return s->ops->llistxattr(&s->ctx, path->data,

                              value, size);

}

static int v9fs_do_lsetxattr(V9fsState *s, V9fsString *path,

                             V9fsString *xattr_name,

                             void *value, size_t size, int flags)

{

    return s->ops->lsetxattr(&s->ctx, path->data,

                             xattr_name->data, value, size, flags);

}

static int v9fs_do_lremovexattr(V9fsState *s, V9fsString *path,

                                V9fsString *xattr_name)

{

    return s->ops->lremovexattr(&s->ctx, path->data,

                                xattr_name->data);

}

static void v9fs_string_init(V9fsString *str)

{

    str->data = NULL;

    str->size = 0;

}

static void v9fs_string_free(V9fsString *str)

{

    qemu_free(str->data);

    str->data = NULL;

    str->size = 0;

}

static void v9fs_string_null(V9fsString *str)

{

    v9fs_string_free(str);

}

static int number_to_string(void *arg, char type)

{

    unsigned int ret = 0;

    switch (type) {

    case 'u': {

        unsigned int num = *(unsigned int *)arg;

        do {

            ret++;

            num = num/10;

        } while (num);

        break;

    }

    default:

        printf("Number_to_string: Unknown number format\n");

        return -1;

    }

    return ret;

}

static int GCC_FMT_ATTR(2, 0)

v9fs_string_alloc_printf(char **strp, const char *fmt, va_list ap)

{

    va_list ap2;

    char *iter = (char *)fmt;

    int len = 0;

    int nr_args = 0;

    char *arg_char_ptr;

    unsigned int arg_uint;

    /* Find the number of %'s that denotes an argument */

    for (iter = strstr(iter, "%"); iter; iter = strstr(iter, "%")) {

        nr_args++;

        iter++;

    }

    len = strlen(fmt) - 2*nr_args;

    if (!nr_args) {

        goto alloc_print;

    }

    va_copy(ap2, ap);

    iter = (char *)fmt;

    /* Now parse the format string */

    for (iter = strstr(iter, "%"); iter; iter = strstr(iter, "%")) {

        iter++;

        switch (*iter) {

        case 'u':

            arg_uint = va_arg(ap2, unsigned int);

            len += number_to_string((void *)&arg_uint, 'u');

            break;

        case 's':

            arg_char_ptr = va_arg(ap2, char *);

            len += strlen(arg_char_ptr);

            break;

        case 'c':

            len += 1;

            break;

        default:

            fprintf(stderr,

                    "v9fs_string_alloc_printf:Incorrect format %c", *iter);

            return -1;

        }

        iter++;

    }

alloc_print:

    *strp = qemu_malloc((len + 1) * sizeof(**strp));

    return vsprintf(*strp, fmt, ap);

}

static void GCC_FMT_ATTR(2, 3)

v9fs_string_sprintf(V9fsString *str, const char *fmt, ...)

{

    va_list ap;

    int err;

    v9fs_string_free(str);

    va_start(ap, fmt);

    err = v9fs_string_alloc_printf(&str->data, fmt, ap);

    BUG_ON(err == -1);

    va_end(ap);

    str->size = err;

}

static void v9fs_string_copy(V9fsString *lhs, V9fsString *rhs)

{

    v9fs_string_free(lhs);

    v9fs_string_sprintf(lhs, "%s", rhs->data);

}

static size_t v9fs_string_size(V9fsString *str)

{

    return str->size;

}

static V9fsFidState *lookup_fid(V9fsState *s, int32_t fid)

{

    V9fsFidState *f;

    for (f = s->fid_list; f; f = f->next) {

        if (f->fid == fid) {

            return f;

        }

    }

    return NULL;

}

static V9fsFidState *alloc_fid(V9fsState *s, int32_t fid)

{

    V9fsFidState *f;

    f = lookup_fid(s, fid);

    if (f) {

        return NULL;

    }

    f = qemu_mallocz(sizeof(V9fsFidState));

    f->fid = fid;

    f->fid_type = P9_FID_NONE;

    f->next = s->fid_list;

    s->fid_list = f;

    return f;

}

static int v9fs_xattr_fid_clunk(V9fsState *s, V9fsFidState *fidp)

{

    int retval = 0;

    if (fidp->fs.xattr.copied_len == -1) {

        /* getxattr/listxattr fid */

        goto free_value;

    }

    /*

     * if this is fid for setxattr. clunk should

     * result in setxattr localcall

     */

    if (fidp->fs.xattr.len != fidp->fs.xattr.copied_len) {

        /* clunk after partial write */

        retval = -EINVAL;

        goto free_out;

    }

    if (fidp->fs.xattr.len) {

        retval = v9fs_do_lsetxattr(s, &fidp->path, &fidp->fs.xattr.name,

                                   fidp->fs.xattr.value,

                                   fidp->fs.xattr.len,

                                   fidp->fs.xattr.flags);

    } else {

        retval = v9fs_do_lremovexattr(s, &fidp->path, &fidp->fs.xattr.name);

    }

free_out:

    v9fs_string_free(&fidp->fs.xattr.name);

free_value:

    if (fidp->fs.xattr.value) {

        qemu_free(fidp->fs.xattr.value);

    }

    return retval;

}

static int free_fid(V9fsState *s, int32_t fid)

{

    int retval = 0;

    V9fsFidState **fidpp, *fidp;

    for (fidpp = &s->fid_list; *fidpp; fidpp = &(*fidpp)->next) {

        if ((*fidpp)->fid == fid) {

            break;

        }

    }

    if (*fidpp == NULL) {

        return -ENOENT;

    }

    fidp = *fidpp;

    *fidpp = fidp->next;

    if (fidp->fid_type == P9_FID_FILE) {

        v9fs_do_close(s, fidp->fs.fd);

    } else if (fidp->fid_type == P9_FID_DIR) {

        v9fs_do_closedir(s, fidp->fs.dir);

    } else if (fidp->fid_type == P9_FID_XATTR) {

        retval = v9fs_xattr_fid_clunk(s, fidp);

    }

    v9fs_string_free(&fidp->path);

    qemu_free(fidp);

    return retval;

}

#define P9_QID_TYPE_DIR         0x80

#define P9_QID_TYPE_SYMLINK     0x02

#define P9_STAT_MODE_DIR        0x80000000

#define P9_STAT_MODE_APPEND     0x40000000

#define P9_STAT_MODE_EXCL       0x20000000

#define P9_STAT_MODE_MOUNT      0x10000000

#define P9_STAT_MODE_AUTH       0x08000000

#define P9_STAT_MODE_TMP        0x04000000

#define P9_STAT_MODE_SYMLINK    0x02000000

#define P9_STAT_MODE_LINK       0x01000000

#define P9_STAT_MODE_DEVICE     0x00800000

#define P9_STAT_MODE_NAMED_PIPE 0x00200000

#define P9_STAT_MODE_SOCKET     0x00100000

#define P9_STAT_MODE_SETUID     0x00080000

#define P9_STAT_MODE_SETGID     0x00040000

#define P9_STAT_MODE_SETVTX     0x00010000

#define P9_STAT_MODE_TYPE_BITS (P9_STAT_MODE_DIR |          \

                                P9_STAT_MODE_SYMLINK |      \

                                P9_STAT_MODE_LINK |         \

                                P9_STAT_MODE_DEVICE |       \

                                P9_STAT_MODE_NAMED_PIPE |   \

                                P9_STAT_MODE_SOCKET)

/* This is the algorithm from ufs in spfs */

static void stat_to_qid(const struct stat *stbuf, V9fsQID *qidp)

{

    size_t size;

    size = MIN(sizeof(stbuf->st_ino), sizeof(qidp->path));

    memcpy(&qidp->path, &stbuf->st_ino, size);

    qidp->version = stbuf->st_mtime ^ (stbuf->st_size << 8);

    qidp->type = 0;

    if (S_ISDIR(stbuf->st_mode)) {

        qidp->type |= P9_QID_TYPE_DIR;

    }

    if (S_ISLNK(stbuf->st_mode)) {

        qidp->type |= P9_QID_TYPE_SYMLINK;

    }

}

static int fid_to_qid(V9fsState *s, V9fsFidState *fidp, V9fsQID *qidp)

{

    struct stat stbuf;

    int err;

    err = v9fs_do_lstat(s, &fidp->path, &stbuf);

    if (err) {

        return err;

    }

    stat_to_qid(&stbuf, qidp);

    return 0;

}

static V9fsPDU *alloc_pdu(V9fsState *s)

{

    V9fsPDU *pdu = NULL;

    if (!QLIST_EMPTY(&s->free_list)) {

        pdu = QLIST_FIRST(&s->free_list);

        QLIST_REMOVE(pdu, next);

    }

    return pdu;

}

static void free_pdu(V9fsState *s, V9fsPDU *pdu)

{

    if (pdu) {

        QLIST_INSERT_HEAD(&s->free_list, pdu, next);

    }

}

size_t pdu_packunpack(void *addr, struct iovec *sg, int sg_count,

                        size_t offset, size_t size, int pack)

{

    int i = 0;

    size_t copied = 0;

    for (i = 0; size && i < sg_count; i++) {

        size_t len;

        if (offset >= sg[i].iov_len) {

            /* skip this sg */

            offset -= sg[i].iov_len;

            continue;

        } else {

            len = MIN(sg[i].iov_len - offset, size);

            if (pack) {

                memcpy(sg[i].iov_base + offset, addr, len);

            } else {

                memcpy(addr, sg[i].iov_base + offset, len);

            }

            size -= len;

            copied += len;

            addr += len;

            if (size) {

                offset = 0;

                continue;

            }

        }

    }

    return copied;

}

static size_t pdu_unpack(void *dst, V9fsPDU *pdu, size_t offset, size_t size)

{

    return pdu_packunpack(dst, pdu->elem.out_sg, pdu->elem.out_num,

                         offset, size, 0);

}

static size_t pdu_pack(V9fsPDU *pdu, size_t offset, const void *src,

                        size_t size)

{

    return pdu_packunpack((void *)src, pdu->elem.in_sg, pdu->elem.in_num,

                             offset, size, 1);

}

static int pdu_copy_sg(V9fsPDU *pdu, size_t offset, int rx, struct iovec *sg)

{

    size_t pos = 0;

    int i, j;

    struct iovec *src_sg;

    unsigned int num;

    if (rx) {

        src_sg = pdu->elem.in_sg;

        num = pdu->elem.in_num;

    } else {

        src_sg = pdu->elem.out_sg;

        num = pdu->elem.out_num;

    }

    j = 0;

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

        if (offset <= pos) {

            sg[j].iov_base = src_sg[i].iov_base;

            sg[j].iov_len = src_sg[i].iov_len;

            j++;

        } else if (offset < (src_sg[i].iov_len + pos)) {

            sg[j].iov_base = src_sg[i].iov_base;

            sg[j].iov_len = src_sg[i].iov_len;

            sg[j].iov_base += (offset - pos);

            sg[j].iov_len -= (offset - pos);

            j++;

        }

        pos += src_sg[i].iov_len;

    }

    return j;

}

static size_t pdu_unmarshal(V9fsPDU *pdu, size_t offset, const char *fmt, ...)

{

    size_t old_offset = offset;

    va_list ap;

    int i;

    va_start(ap, fmt);

    for (i = 0; fmt[i]; i++) {

        switch (fmt[i]) {

        case 'b': {

            uint8_t *valp = va_arg(ap, uint8_t *);

            offset += pdu_unpack(valp, pdu, offset, sizeof(*valp));

            break;

        }

        case 'w': {

            uint16_t val, *valp;

            valp = va_arg(ap, uint16_t *);

            val = le16_to_cpupu(valp);

            offset += pdu_unpack(&val, pdu, offset, sizeof(val));

            *valp = val;

            break;

        }

        case 'd': {

            uint32_t val, *valp;

            valp = va_arg(ap, uint32_t *);

            val = le32_to_cpupu(valp);

            offset += pdu_unpack(&val, pdu, offset, sizeof(val));

            *valp = val;

            break;

        }

        case 'q': {

            uint64_t val, *valp;

            valp = va_arg(ap, uint64_t *);

            val = le64_to_cpup(valp);

            offset += pdu_unpack(&val, pdu, offset, sizeof(val));

            *valp = val;

            break;

        }

        case 'v': {

            struct iovec *iov = va_arg(ap, struct iovec *);

            int *iovcnt = va_arg(ap, int *);

            *iovcnt = pdu_copy_sg(pdu, offset, 0, iov);

            break;

        }

        case 's': {

            V9fsString *str = va_arg(ap, V9fsString *);

            offset += pdu_unmarshal(pdu, offset, "w", &str->size);

            /* FIXME: sanity check str->size */

            str->data = qemu_malloc(str->size + 1);

            offset += pdu_unpack(str->data, pdu, offset, str->size);

            str->data[str->size] = 0;

            break;

        }

        case 'Q': {

            V9fsQID *qidp = va_arg(ap, V9fsQID *);

            offset += pdu_unmarshal(pdu, offset, "bdq",

                        &qidp->type, &qidp->version, &qidp->path);

            break;

        }

        case 'S': {

            V9fsStat *statp = va_arg(ap, V9fsStat *);

            offset += pdu_unmarshal(pdu, offset, "wwdQdddqsssssddd",

                        &statp->size, &statp->type, &statp->dev,

                        &statp->qid, &statp->mode, &statp->atime,

                        &statp->mtime, &statp->length,

                        &statp->name, &statp->uid, &statp->gid,

                        &statp->muid, &statp->extension,

                        &statp->n_uid, &statp->n_gid,

                        &statp->n_muid);

            break;

        }

        case 'I': {

            V9fsIattr *iattr = va_arg(ap, V9fsIattr *);

            offset += pdu_unmarshal(pdu, offset, "ddddqqqqq",

                        &iattr->valid, &iattr->mode,

                        &iattr->uid, &iattr->gid, &iattr->size,

                        &iattr->atime_sec, &iattr->atime_nsec,

                        &iattr->mtime_sec, &iattr->mtime_nsec);

            break;

        }

        default:

            break;

        }

    }

    va_end(ap);

    return offset - old_offset;

}

static size_t pdu_marshal(V9fsPDU *pdu, size_t offset, const char *fmt, ...)

{

    size_t old_offset = offset;

    va_list ap;

    int i;

    va_start(ap, fmt);

    for (i = 0; fmt[i]; i++) {

        switch (fmt[i]) {

        case 'b': {

            uint8_t val = va_arg(ap, int);

            offset += pdu_pack(pdu, offset, &val, sizeof(val));

            break;

        }

        case 'w': {

            uint16_t val;

            cpu_to_le16w(&val, va_arg(ap, int));

            offset += pdu_pack(pdu, offset, &val, sizeof(val));

            break;

        }

        case 'd': {

            uint32_t val;

            cpu_to_le32w(&val, va_arg(ap, uint32_t));

            offset += pdu_pack(pdu, offset, &val, sizeof(val));

            break;

        }

        case 'q': {

            uint64_t val;

            cpu_to_le64w(&val, va_arg(ap, uint64_t));

            offset += pdu_pack(pdu, offset, &val, sizeof(val));

            break;

        }

        case 'v': {

            struct iovec *iov = va_arg(ap, struct iovec *);

            int *iovcnt = va_arg(ap, int *);

            *iovcnt = pdu_copy_sg(pdu, offset, 1, iov);

            break;

        }

        case 's': {

            V9fsString *str = va_arg(ap, V9fsString *);

            offset += pdu_marshal(pdu, offset, "w", str->size);

            offset += pdu_pack(pdu, offset, str->data, str->size);

            break;

        }

        case 'Q': {

            V9fsQID *qidp = va_arg(ap, V9fsQID *);

            offset += pdu_marshal(pdu, offset, "bdq",

                        qidp->type, qidp->version, qidp->path);

            break;

        }

        case 'S': {

            V9fsStat *statp = va_arg(ap, V9fsStat *);

            offset += pdu_marshal(pdu, offset, "wwdQdddqsssssddd",

                        statp->size, statp->type, statp->dev,

                        &statp->qid, statp->mode, statp->atime,

                        statp->mtime, statp->length, &statp->name,

                        &statp->uid, &statp->gid, &statp->muid,

                        &statp->extension, statp->n_uid,

                        statp->n_gid, statp->n_muid);

            break;

        }

        case 'A': {

            V9fsStatDotl *statp = va_arg(ap, V9fsStatDotl *);

            offset += pdu_marshal(pdu, offset, "qQdddqqqqqqqqqqqqqqq",

                        statp->st_result_mask,

                        &statp->qid, statp->st_mode,

                        statp->st_uid, statp->st_gid,

                        statp->st_nlink, statp->st_rdev,

                        statp->st_size, statp->st_blksize, statp->st_blocks,

                        statp->st_atime_sec, statp->st_atime_nsec,

                        statp->st_mtime_sec, statp->st_mtime_nsec,

                        statp->st_ctime_sec, statp->st_ctime_nsec,

                        statp->st_btime_sec, statp->st_btime_nsec,

                        statp->st_gen, statp->st_data_version);

            break;

        }

        default:

            break;

        }

    }

    va_end(ap);

    return offset - old_offset;

}

static void complete_pdu(V9fsState *s, V9fsPDU *pdu, ssize_t len)

{

    int8_t id = pdu->id + 1; /* Response */

    if (len < 0) {

        int err = -len;

        len = 7;

        if (s->proto_version != V9FS_PROTO_2000L) {

            V9fsString str;

            str.data = strerror(err);

            str.size = strlen(str.data);

            len += pdu_marshal(pdu, len, "s", &str);

            id = P9_RERROR;

        }

        len += pdu_marshal(pdu, len, "d", err);

        if (s->proto_version == V9FS_PROTO_2000L) {

            id = P9_RLERROR;

        }

    }

    /* fill out the header */

    pdu_marshal(pdu, 0, "dbw", (int32_t)len, id, pdu->tag);

    /* keep these in sync */

    pdu->size = len;

    pdu->id = id;

    /* push onto queue and notify */

    virtqueue_push(s->vq, &pdu->elem, len);

    /* FIXME: we should batch these completions */

    virtio_notify(&s->vdev, s->vq);

    free_pdu(s, pdu);

}

static mode_t v9mode_to_mode(uint32_t mode, V9fsString *extension)

{

    mode_t ret;

    ret = mode & 0777;

    if (mode & P9_STAT_MODE_DIR) {

        ret |= S_IFDIR;

    }

    if (mode & P9_STAT_MODE_SYMLINK) {

        ret |= S_IFLNK;

    }

    if (mode & P9_STAT_MODE_SOCKET) {

        ret |= S_IFSOCK;

    }

    if (mode & P9_STAT_MODE_NAMED_PIPE) {

        ret |= S_IFIFO;

    }

    if (mode & P9_STAT_MODE_DEVICE) {

        if (extension && extension->data[0] == 'c') {

            ret |= S_IFCHR;

        } else {

            ret |= S_IFBLK;

        }

    }

    if (!(ret&~0777)) {