Messages in this thread |  | | Date | Thu, 4 Jan 2024 15:33:04 -0500 | | From | Steven Rostedt <> | | Subject | Re: [for-next][PATCH 2/3] eventfs: Stop using dcache_readdir() for getdents() |
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On Thu, 4 Jan 2024 12:18:06 -0800 Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Thu, 4 Jan 2024 at 12:04, Steven Rostedt <rostedt@goodmis.org> wrote: > > > > Also, I just realized it breaks if we update the 'c--' before the callback. :-/ > > > > I have to put this check *after* the callback check. > > What? No. > > > Reason being, the callback can say "this event doesn't get this file" and > > return 0, which tells eventfs to skip this file. > > So yes, there seems to be a bug there, in that ctx->pos is only > updated for successful callbacks (and not for "ignored entry").
OK, I wasn't sure if it was OK to update the ctx->pos for something we didn't add, so I avoided doing so.
> > But that just means that you should always update 'ctx->pos' as you > 'continue' the loop. > > The logical place to do that would be in the for-loop itself, which > actually is very natural for the simple case, ie you should just do > > for (i = 0; i < ei->nr_entries; i++, ctx->pos++) {
Well, we don't want to do that and c-- at the same time. But of course, if we do the shortcut, we can have:
for (i = c; i < ei->nr_entries; i++, ctx->pos++) {
which would be OK. And better if we move it before the ei->children list walk.
> > but in the list_for_each_entry_srcu() case the 'update' part of the > for-loop isn't actually accessible, so it would have to be at the > 'continue' point(s). > > Which is admittedly a bit annoying.
But not really an issue as we just have:
list_for_each_entry_srcu(ei_child, &ei->children, list, srcu_read_lock_held(&eventfs_srcu)) {
if (c > 0) { c--; continue; }
ctx->pos++;
> > Looking at that I'm actually surprised that I don't recall that we'd > have hit that issue with our 'for_each_xyz()' loops before. > > The update for our "for_each_xyz()" helpers are all hardcoded to just > do the "next iterator" thing, and there's no nice way to take > advantage of the normal for-loop semantics of "do this at the end of > the loop"
Anyway, if I do count ctx->pos++ for every iteration, whether it added something or not, it appears to work. I'll write up a couple of patches to handle this.
Thanks,
-- Steve
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