On Mon, 1 Dec 2014 21:19:12 -0500 Theodore Ts'o <ty...@mit.edu> wrote:
> I was trying to do something like this: > > filter="events/writeback/writeback_mark_inode_dirty/filter" > echo "(flags & 2048) && ((state & 2048) == 0)" > $filter > > ... but that doesn't work. > > This works: > > echo "flags & 2048" > $filter > > But the problem is this: > > echo "(state & 2048) == 0" > $filter > > The simplest patch to add this would be add a new filter_ops so we > could do this: > > echo "(state !& 2048)" > $filter > > ... but that's pretty ugly. But adding more general expression > parsing in the ftrace event filter code would be non-trivial, and if > we start trying to make things like "!(state & 2048)" or "(state & > 2048) == 0", then at some point some crazy person might request > supporting something like this: "(state ^ flags) == 2048". :-) > > So I guess the main question I want to ask is your opinion about > whether a patch that adds support for the operator "!&" is too ugly to > live? > Yeah, I don't want to add some bastardization compare that we'll be stuck with till the end of time. Either we modify the tree walk to handle values (it shouldn't be too difficult, but it wont be trivial), or we wait till eBPF is up and running as the trace filter replacement and that should be able to handle this much better. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
