Hi, On 2020-03-09 18:49:31 -0400, Jeff Layton wrote: > On Mon, 2020-03-09 at 12:22 -0700, Andres Freund wrote: > > On 2020-03-09 13:50:59 -0400, Jeff Layton wrote: > > > I sent a patch a few weeks ago to make syncfs() return errors when there > > > have been writeback errors on the superblock. It's not merged yet, but > > > once we have something like that in place, we could expose info from the > > > errseq_t to userland using this interface. > > > > I'm still a bit worried about the details of errseq_t being exposed to > > userland. Partially because it seems to restrict further evolution of > > errseq_t, and partially because it will likely up with userland trying > > to understand it (it's e.g. just too attractive to report a count of > > errors etc). > > Trying to interpret the counter field won't really tell you anything. > The counter is not incremented unless someone has queried the value > since it was last checked. A single increment could represent a single > writeback error or 10000 identical ones. Oh, right. A zero errseq would still indicate something, but that's probably fine. > > Is there a reason to not instead report a 64bit counter instead of the > > cookie? In contrast to the struct file case we'd only have the space > > overhead once per superblock, rather than once per #files * #fd. And it > > seems that the maintenance of that counter could be done without > > widespread changes, e.g. instead/in addition to your change: > What problem would moving to a 64-bit counter solve? I get the concern > about people trying to get a counter out of the cookie field, but giving > people an explicit 64-bit counter seems even more open to > misinterpretation. Well, you could get an actual error count out of it? I was thinking that that value would get incremented every time mapping_set_error() is called, which should make it a meaningful count? Greetings, Andres Freund
