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

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 ();