On Tue, Jul 31, 2018 at 10:51:57PM +0000, Mark Fasheh wrote: > Hi Al, > > On Tue, Jul 31, 2018 at 11:16:05PM +0100, Al Viro wrote: > > On Tue, Jul 31, 2018 at 02:10:43PM -0700, Mark Fasheh wrote: > > > ->getattr from inside the kernel won't always have a vfsmount, check for > > > this. > > > > Really? Where would that happen? > > It happens in my first patch. FWIW, I'm not tied to that particular bit of > code, or even this (latest) approach. I would actually very much appreciate > your input into how we might fix the problem we have where we are sometimes > not exporting a correct ino/dev pair to user space. Which callers would those be? I don't see anything in your series that wouldn't have vfsmount at hand... > I have a good break-down of the problem and possible solutions here: > > https://www.spinics.net/lists/linux-fsdevel/msg128003.html btrfs pulling odd crap with device numbers is a problem, but this is far from the most obvious unpleasantness caused by that - e.g. userland code expecting that unequal st_dev for directory and subdirectory means that we have a mountpoint there. Or assuming it can compare that to st_dev of mountpoints (or, indeed, the values in /proc/self/mountinfo) to find which fs it's on... /proc/*/maps is unfortunate, but it does contain the pathnames, doesn't it? What _real_ problems are there - the ones where we don't have a saner solution? Note that /proc/locks is (a) FPOS interface and (b) unsuitable for your approach anyway.
