[Qemu-devel] Re: [V9fs-developer] [PATCH] qemu:virtio-9p: Send iounit to client for read/write operations

["Venkateswararao Jujjuri (JV)" <jvrao@linux.vnet.ibm.com>]

M. Mohan Kumar 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>
> Reviewd-by: Sripathi Kodi <sripathik@in.ibm.com>
> ---
>  hw/virtio-9p.c |   69 +++++++++++++++++++++++++++++++++++++++++++++----------
>  hw/virtio-9p.h |    7 +++++
>  2 files changed, 63 insertions(+), 13 deletions(-)
> 
> This patch depends on the patch
> http://lists.nongnu.org/archive/html/qemu-devel/2010-05/msg02706.html
> 
> diff --git a/hw/virtio-9p.c b/hw/virtio-9p.c
> index 851004d..c60dcc8 100644
> --- a/hw/virtio-9p.c
> +++ b/hw/virtio-9p.c
> @@ -258,6 +258,11 @@ 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;
> @@ -1067,11 +1072,10 @@ 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;
> @@ -1081,7 +1085,7 @@ 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);
> @@ -1515,6 +1519,26 @@ out:
>      v9fs_walk_complete(s, vs, err);
>  }
> 
> +static int32_t get_iounit(V9fsState *s, V9fsString *name)
> +{
> +    struct statfs stbuf;
> +    int32_t iounit = 0;
> +
> +    /*
> +     * iounit should be multiples of f_bsize (host filesystem block size
> +     * and as well as less than (client msize - P9_IOHDRSZ))
> +     */
> +    if (!v9fs_do_statfs(s, name, &stbuf)) {
> +        iounit = stbuf.f_bsize;
> +        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;
> +    }
> +
> +    if (!iounit) {
> +        iounit = s->msize - P9_IOHDRSZ;
> +    }
> +    return iounit;
> +}
> +
>  static void v9fs_open_post_opendir(V9fsState *s, V9fsOpenState *vs, int err)
>  {
>      if (vs->fidp->dir == NULL) {
> @@ -1532,12 +1556,15 @@ 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);
> @@ -2011,11 +2038,16 @@ out:
> 
>  static void v9fs_post_create(V9fsState *s, V9fsCreateState *vs, int err)
>  {
> +    int32_t iounit;
> +
> +    iounit = get_iounit(s, &vs->fidp->path);

Now get_iounit() does a statfs() system call..hence I think we need to introduce a
state/post function  here.

- JV

> +
>      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;
>      }
> @@ -2654,23 +2686,34 @@ 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;
>      }
> 
> +    /*
> +     * compute bsize factor based on host file system block size
> +     * and client msize
> +     */
> +    bsize_factor = (s->msize - P9_IOHDRSZ)/vs->stbuf.f_bsize;
> +    if (!bsize_factor) {
> +        bsize_factor = 1;
> +    }
>      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;
> +    /*
> +     * f_bsize is adjusted(multiplied) by bsize factor, so we need to
> +     * adjust(divide) the number of blocks, free blocks and available
> +     * blocks by 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 3819be5..92bbeb0 100644
> --- a/hw/virtio-9p.h
> +++ b/hw/virtio-9p.h
> @@ -84,6 +84,12 @@ enum p9_proto_version {
>  #define P9_NOFID    (u32)(~0)
>  #define P9_MAXWELEM 16
> 
> +/*
> + * ample room for Twrite/Rread header
> + * size[4] Tread/Twrite tag[2] fid[4] offset[8] count[4]
> + */
> +#define P9_IOHDRSZ 24
> +
>  typedef struct V9fsPDU V9fsPDU;
> 
>  struct V9fsPDU
> @@ -168,6 +174,7 @@ typedef struct V9fsState
>      uint8_t *tag;
>      size_t config_size;
>      enum p9_proto_version proto_version;
> +    int32_t msize;
>  } V9fsState;
> 
>  typedef struct V9fsCreateState {