Re: [PATCH 1/2] 9pfs: deduplicate iounit code

[Greg Kurz]

On Mon, 27 Sep 2021 17:45:00 +0200
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> Remove redundant code that translates host fileystem's block
> size into 9p client (guest side) block size.
> 
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> ---
>  hw/9pfs/9p.c | 42 ++++++++++++++++++++----------------------
>  1 file changed, 20 insertions(+), 22 deletions(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 708b030474..c65584173a 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -1262,18 +1262,26 @@ static int coroutine_fn stat_to_v9stat(V9fsPDU *pdu, 
> V9fsPath *path,
>  #define P9_STATS_ALL           0x00003fffULL /* Mask for All fields above */
>  
>  
> -static int32_t stat_to_iounit(const V9fsPDU *pdu, const struct stat *stbuf)
> +/**
> + * Convert host filesystem's block size into an appropriate block size for
> + * 9p client (guest OS side). The value returned suggests an "optimum" block
> + * size for 9p I/O, i.e. to maximize performance.
> + *
> + * @pdu: 9p client request
> + * @blksize: host filesystem's block size
> + */
> +static int32_t blksize_to_iounit(const V9fsPDU *pdu, int32_t blksize)
>  {
>      int32_t iounit = 0;
>      V9fsState *s = pdu->s;
>  
>      /*
> -     * iounit should be multiples of st_blksize (host filesystem block size)
> +     * iounit should be multiples of blksize (host filesystem block size)
>       * as well as less than (client msize - P9_IOHDRSZ)
>       */
> -    if (stbuf->st_blksize) {
> -        iounit = stbuf->st_blksize;
> -        iounit *= (s->msize - P9_IOHDRSZ) / stbuf->st_blksize;
> +    if (blksize) {
> +        iounit = blksize;
> +        iounit *= (s->msize - P9_IOHDRSZ) / blksize;
>      }
>      if (!iounit) {
>          iounit = s->msize - P9_IOHDRSZ;
> @@ -1281,6 +1289,11 @@ static int32_t stat_to_iounit(const V9fsPDU *pdu, 
> const struct stat *stbuf)
>      return iounit;
>  }
>  
> +static int32_t stat_to_iounit(const V9fsPDU *pdu, const struct stat *stbuf)
> +{
> +    return blksize_to_iounit(pdu, stbuf->st_blksize);
> +}
> +
>  static int stat_to_v9stat_dotl(V9fsPDU *pdu, const struct stat *stbuf,
>                                  V9fsStatDotl *v9lstat)
>  {
> @@ -1899,23 +1912,8 @@ out_nofid:
>  static int32_t coroutine_fn get_iounit(V9fsPDU *pdu, V9fsPath *path)
>  {
>      struct statfs stbuf;
> -    int32_t iounit = 0;
> -    V9fsState *s = pdu->s;
> -
> -    /*
> -     * iounit should be multiples of f_bsize (host filesystem block size
> -     * and as well as less than (client msize - P9_IOHDRSZ))
> -     */
> -    if (!v9fs_co_statfs(pdu, path, &stbuf)) {
> -        if (stbuf.f_bsize) {
> -            iounit = stbuf.f_bsize;
> -            iounit *= (s->msize - P9_IOHDRSZ) / stbuf.f_bsize;
> -        }
> -    }
> -    if (!iounit) {
> -        iounit = s->msize - P9_IOHDRSZ;
> -    }
> -    return iounit;
> +    int err = v9fs_co_statfs(pdu, path, &stbuf);

It is usually preferred to leave a blank line between declarations
and statements for easier reading. It isn't mandated in the coding
style but Markus consistently asks for it :-) Maybe you can fix
that before pushing to 9p.next ?

Reviewed-by: Greg Kurz <groug@kaod.org>

> +    return blksize_to_iounit(pdu, (err >= 0) ? stbuf.f_bsize : 0);
>  }
>  
>  static void coroutine_fn v9fs_open(void *opaque)