Re: [Qemu-devel] qemu:virtio-9p: [RFC] [PATCH 01/02] Send iounit to client for read/write operations

[Sripathi Kodi <sripathik@in.ibm.com>]

On Tue,  1 Jun 2010 19:47:14 +0530
"M. Mohan Kumar" <mohan@in.ibm.com> wrote:

> Compute iounit based on the host filesystem block size and pass it to
> client with open/create response. Also return iounit as statfs's f_bsize
> for optimal block size transfers.
> 
> Signed-off-by: M. Mohan Kumar <mohan@in.ibm.com>
> ---
>  hw/virtio-9p.c |   56 ++++++++++++++++++++++++++++++++++++++++++--------------
>  hw/virtio-9p.h |    3 +++
>  2 files changed, 45 insertions(+), 14 deletions(-)
> 
> diff --git a/hw/virtio-9p.c b/hw/virtio-9p.c
> index f087122..4357f1f 100644
> --- a/hw/virtio-9p.c
> +++ b/hw/virtio-9p.c
> @@ -1,4 +1,4 @@
> -/*
> +		/*
>   * Virtio 9p backend
>   *
>   * Copyright IBM, Corp. 2010
> @@ -269,6 +269,11 @@ 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 void v9fs_string_init(V9fsString *str)
>  {
>      str->data = NULL;
> @@ -1035,11 +1040,10 @@ static void v9fs_fix_path(V9fsString *dst, V9fsString *src, int len)
> 
>  static void v9fs_version(V9fsState *s, V9fsPDU *pdu)
>  {
> -    int32_t msize;
>      V9fsString version;
>      size_t offset = 7;
> 
> -    pdu_unmarshal(pdu, offset, "ds", &msize, &version);
> +    pdu_unmarshal(pdu, offset, "ds", &s->msize, &version);
> 
>      if (!strcmp(version.data, "9P2000.u")) {
>          s->proto_version = V9FS_PROTO_2000U;
> @@ -1049,7 +1053,7 @@ static void v9fs_version(V9fsState *s, V9fsPDU *pdu)
>          v9fs_string_sprintf(&version, "unknown");
>      }
> 
> -    offset += pdu_marshal(pdu, offset, "ds", msize, &version);
> +    offset += pdu_marshal(pdu, offset, "ds", s->msize, &version);
>      complete_pdu(s, pdu, offset);
> 
>      v9fs_string_free(&version);
> @@ -1304,6 +1308,20 @@ out:
>      v9fs_walk_complete(s, vs, err);
>  }
> 
> +static int32_t get_iounit(V9fsState *s, V9fsString *name)
> +{
> +    struct statfs stbuf;
> +    int32_t iounit = 0;
> +
> +
> +    if (!v9fs_do_statfs(s, name, &stbuf)) {
> +        iounit = stbuf.f_bsize;
> +        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;

If (s->msize - P9_IOHDRSZ) is less than stbuf.f_bsize iounit becomes
zero. See below.

> +    }
> +
> +    return iounit;
> +}
> +
>  static void v9fs_open_post_opendir(V9fsState *s, V9fsOpenState *vs, int err)
>  {
>      if (vs->fidp->dir == NULL) {
> @@ -1321,12 +1339,15 @@ out:
> 
>  static void v9fs_open_post_open(V9fsState *s, V9fsOpenState *vs, int err)
>  {
> +    int32_t iounit;
> +
>      if (vs->fidp->fd == -1) {
>          err = -errno;
>          goto out;
>      }
> 
> -    vs->offset += pdu_marshal(vs->pdu, vs->offset, "Qd", &vs->qid, 0);
> +    iounit = get_iounit(s, &vs->fidp->path);
> +    vs->offset += pdu_marshal(vs->pdu, vs->offset, "Qd", &vs->qid, iounit);
>      err = vs->offset;
>  out:
>      complete_pdu(s, vs->pdu, err);
> @@ -1800,11 +1821,16 @@ out:
> 
>  static void v9fs_post_create(V9fsState *s, V9fsCreateState *vs, int err)
>  {
> +    int32_t iounit;
> +
> +    iounit = get_iounit(s, &vs->fidp->path);
> +
>      if (err == 0) {
>          v9fs_string_copy(&vs->fidp->path, &vs->fullname);
>          stat_to_qid(&vs->stbuf, &vs->qid);
> 
> -        vs->offset += pdu_marshal(vs->pdu, vs->offset, "Qd", &vs->qid, 0);
> +        vs->offset += pdu_marshal(vs->pdu, vs->offset, "Qd", &vs->qid,
> +                iounit);
> 
>          err = vs->offset;
>      }
> @@ -2295,23 +2321,25 @@ out:
>      qemu_free(vs);
>  }
> 
> -static int v9fs_do_statfs(V9fsState *s, V9fsString *path, struct statfs *stbuf)
> -{
> -    return s->ops->statfs(&s->ctx, path->data, stbuf);
> -}
> -
>  static void v9fs_statfs_post_statfs(V9fsState *s, V9fsStatfsState *vs, int err)
>  {
> +    int32_t bsize_factor;
> +
>      if (err) {
>          err = -errno;
>          goto out;
>      }
> 
> +    bsize_factor = (s->msize - P9_IOHDRSZ)/vs->stbuf.f_bsize;
> +    if (!bsize_factor) {
> +        bsize_factor = 1;
> +    }

Again, if (s->msize - P9_IOHDRSZ) is less than stbuf.f_bsize
bsize_factor becomes zero. The following divisions become divide by
zero!

Thanks,
Sripathi.

>      vs->v9statfs.f_type = vs->stbuf.f_type;
>      vs->v9statfs.f_bsize = vs->stbuf.f_bsize;
> -    vs->v9statfs.f_blocks = vs->stbuf.f_blocks;
> -    vs->v9statfs.f_bfree = vs->stbuf.f_bfree;
> -    vs->v9statfs.f_bavail = vs->stbuf.f_bavail;
> +    vs->v9statfs.f_bsize *= bsize_factor;
> +    vs->v9statfs.f_blocks = vs->stbuf.f_blocks/bsize_factor;
> +    vs->v9statfs.f_bfree = vs->stbuf.f_bfree/bsize_factor;
> +    vs->v9statfs.f_bavail = vs->stbuf.f_bavail/bsize_factor;
>      vs->v9statfs.f_files = vs->stbuf.f_files;
>      vs->v9statfs.f_ffree = vs->stbuf.f_ffree;
>      vs->v9statfs.fsid_val = (unsigned int) vs->stbuf.f_fsid.__val[0] |
> diff --git a/hw/virtio-9p.h b/hw/virtio-9p.h
> index 6b3d4a4..9264163 100644
> --- a/hw/virtio-9p.h
> +++ b/hw/virtio-9p.h
> @@ -72,6 +72,8 @@ enum p9_proto_version {
>  #define P9_NOFID    (u32)(~0)
>  #define P9_MAXWELEM 16
> 
> +#define P9_IOHDRSZ 24
> +
>  typedef struct V9fsPDU V9fsPDU;
> 
>  struct V9fsPDU
> @@ -156,6 +158,7 @@ typedef struct V9fsState
>      uint8_t *tag;
>      size_t config_size;
>      enum p9_proto_version proto_version;
> +    int32_t msize;
>  } V9fsState;
> 
>  typedef struct V9fsCreateState {
> -- 
> 1.6.6.1
> 
>