Adding Stefan Raspl, who has done a lot of kvm_stat work in the past. On 05.05.20 19:21, Paolo Bonzini wrote: > On 05/05/20 19:07, David Rientjes wrote: >>> I am totally in favor of having a binary format, but it should be >>> introduced as a separate series on top of this one---and preferably by >>> someone who has already put some thought into the problem (which >>> Emanuele and I have not, beyond ensuring that the statsfs concept and >>> API is flexible enough). >>> >> The concern is that once this series is merged then /sys/kernel/stats >> could be considered an ABI and there would be a reasonable expectation >> that it will remain stable, in so far as the stats that userspace is >> interested in are stable and not obsoleted. >> >> So is this a suggestion that the binary format becomes complementary to >> statsfs and provide a means for getting all stats from a single subsystem, >> or that this series gets converted to such a format before it is merged? > > The binary format should be complementary. The ASCII format should > indeed be considered stable even though individual statistics would come > and go. It may make sense to allow disabling ASCII files via mount > and/or Kconfig options; but either way, the binary format can and should > be added on top. > > I have not put any thought into what the binary format would look like > and what its features would be. For example these are but the first > questions that come to mind: > > * would it be possible to read/clear an arbitrary statistic with > pread/pwrite, or do you have to read all of them? > > * if userspace wants to read the schema just once and then read the > statistics many times, how is it informed of schema changes? > > * and of course the details of how the schema (names of stat and > subsources) is encoded and what details it should include about the > values (e.g. type or just signedness). > > Another possibility is to query stats via BPF. This could be a third > way to access the stats, or it could be alternative to a binary format. > > Paolo >
