On Sat, May 07, 2022 at 07:03:13PM +0300, Amir Goldstein wrote: > Sorry Matthew, I was looking at the code to give you pointers, but there were > so many subtle details (as Jan has expected) that I could only communicate > them with a patch. > I tested that this patch does not break anything, but did not implement the > UAPI changes, so the functionality that it adds is not tested - I leave that > to you. No, that's totally fine. I had to familiarize myself with the FS/FAN_RENAME implementation as I hadn't gone over that series. So appreciate you whipping this together quickly as it would've taken a fair bit of time. Before the UAPI related modifications, we need to first figure out how we are to handle the CREATE/DELETE/MOVE cases. ... > My 0.02$ - while FAN_RENAME is a snowflake, this is not because > of our design, this is because rename(2) is a snowflake vfs operation. > The event information simply reflects the operation complexity and when > looking at non-Linux filesystem event APIs, the event information for rename > looks very similar to FAN_RENAME. In some cases (lustre IIRC) the protocol > was enhanced at some point exactly as we did with FAN_RENAME to > have all the info in one event vs. having to join two events. > > Hopefully, the attached patch simplifies the specialized implementation > a little bit. > > But... (there is always a but when it comes to UAPI), > When looking at my patch, one cannot help wondering - > what about FAN_CREATE/FAN_DELETE/FAN_MOVE? > If those can report child fid, why should they be treated differently > than FAN_RENAME w.r.t marking the child inode? This is something that crossed my mind while looking over the patch and is a very good thing to call-out indeed. I am of the opinion that we shouldn't be placing FAN_RENAME in the special egg basket and also consider how this is to operate for events FAN_CREATE/FAN_DELETE/FAN_MOVE. > For example, when watching a non-dir for FAN_CREATE, it could > be VERY helpful to get the dirfid+name of where the inode was > hard linked. Oh right, here you're referring to this specific scenario: - FAN_CREATE mark exclusively placed on /dir1/old_file - Create link(/dir1/old_file, /dir2/new_file) - Expect to receive single event including two information records FID(/dir1/old_file) + DFID_NAME(/dir2/new_file) Is that correct? > In fact, if an application is watching FAN_RENAME to track the > movement of a non-dir file and does not watch hardlink+unlink, then > the file could escape under the application's nose. That's understood. /M
