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

[Greg Kurz <groug@kaod.org>]

On Mon, 27 Sep 2021 18:50:12 +0200
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> On Montag, 27. September 2021 18:27:59 CEST Greg Kurz wrote:
> > 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 ?
> 
> In general: I adapt to whatever code style is preferred.
> 
> I actually did run (like usual) scripts/checkpatch.pl and it did not complain.
> 

Yes, this isn't enforced nor checked.

> So you mean it is preferred to split up declaration and definition due to the 
> function call involved? I.e. precisely:
> 

Not splitting declaration and definitions but rather the declarations
from the actual code.

> static int32_t coroutine_fn get_iounit(V9fsPDU *pdu, V9fsPath *path)
> {
>     struct statfs stbuf;
>     int err;
> 
>     err = v9fs_co_statfs(pdu, path, &stbuf);
>     return blksize_to_iounit(pdu, (err >= 0) ? stbuf.f_bsize : 0);
> }
> 
> or rather :) ...
> 
> static int32_t coroutine_fn get_iounit(V9fsPDU *pdu, V9fsPath *path)
> {
>     struct statfs stbuf;
>     int err = v9fs_co_statfs(pdu, path, &stbuf);
> 
>     return blksize_to_iounit(pdu, (err >= 0) ? stbuf.f_bsize : 0);
> }
> 
> We actually have mixed declaration/definition all over the place.
> 

It is okay to have mixed declarations/definitions. Second one is fine :)

> > 
> > 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)
> 
>