[Libguestfs] [PATCH 9/9] filters: Move rdelay/wdelay from file plugin to new delay filter.

[Richard W.M. Jones]

On Wed, Jan 17, 2018 at 04:38:04PM -0600, Eric Blake wrote:
> > +/* Zero data. */
> > +static int
> > +delay_zero (struct nbdkit_next *next, void *nxdata,
> > +            void *handle, uint32_t count, uint64_t offset, int may_trim)
> > +{
> > +  write_delay ();
> > +  return next->zero (nxdata, count, offset, may_trim);
> 
> If next->zero() fails with EOPNOTSUPP, that means we will delay once in
> trying the underlying command, and again for each iteration of the
> fallback loop as it calls delay_pwrite().  Is that okay, or do we want
> to reproduce some fallback logic here and directly call next->pwrite on
> EOPNOTSUPP so as to only have a single write delay in that case?

Good point.  How about this, it seems simpler:

  static int
  delay_zero (struct nbdkit_next *next, void *nxdata,
              void *handle, uint32_t count, uint64_t offset, int may_trim)
  {
    int r = next->zero (nxdata, count, offset, may_trim);

    if (r != -1)
      write_delay ();
    return r;
  }

And the same for the other methods in that filter.

Rich.

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