On Fri, Dec 11, 2020 at 05:29:31PM +0000, Al Viro wrote: > On Fri, Dec 11, 2020 at 09:21:20AM -0800, Linus Torvalds wrote: > > On Fri, Dec 11, 2020 at 7:57 AM Jens Axboe <axboe@xxxxxxxxx> wrote: > > > > > > On 12/10/20 7:35 PM, Al Viro wrote: > > > > _IF_ for some theoretical exercise you want to do "lookup without dropping > > > > out of RCU", just add a flag that has unlazy_walk() fail. With -ECHILD. > > > > Strip it away in complete_walk() and have path_init() with that flag > > > > and without LOOKUP_RCU fail with -EAGAIN. All there is to it. > > > > > > Thanks Al, that makes for an easier implementation. I like that suggestion, > > > boils it down to just three hunks (see below). > > > > Ooh. Yes, very nice. > > Except for the wrong order in path_init() - the check should go _before_ > if (!*s) > flags &= ~LOOKUP_RCU; > for obvious reasons. > > Again, that part is trivial - what to do with do_open()/open_last_lookups() > is where the nastiness will be. Basically, it makes sure we bail out in > cases when lookup itself would've blocked, but it does *not* bail out > when equally heavy (and unlikely) blocking sources hit past the complete_walk(). > Which makes it rather useless for the caller, unless we get logics added to > that part as well. And _that_ I want to see before we commit to anything. BTW, to reiterate - "any open that isn't non-blocking" is misleading; it's *NOT* just a matter of passing O_NDELAY in flags.
