David it seem you walked my road already... :-) I'm actually on a research project, so I do not care too much about the issues on existing programs. I'm going to change/break them anyway. Also, as far as I can foresee, it should be viable to fix such programs in a partially automated way (eg via sed and a new "ocreate" library function that mimic the current behaviour).
But reading that thread I can't actually see why the OEXCL path has been taken instead of eliminating the race mapping the syscall to the 9p message. I mean except backward compatibility. Maybe it was found a performance issue in some more common use case? Or a worse race prevented by the current semantic? For example I've found pretty cryptic this message from David: http://marc.info/?l=9fans&m=111558704718797&w=2 I'm surprised I haven't yet seen "What about union directories?" > > If create(2) is changed then it could succeed even though a > file with that name exists in the union. Then the above: > > if ((fd = create(file, mode, perm)) < 0) { > error... > } > > Would need to become: > > if ((fd = open(file, mode|OTRUNC)) < 0 || > (fd = create(file, mode, perm)) < 0 || > (fd = open(file, mode|OTRUNC)) < 0 || > error... > } > > This is precisely the current create(2) call and the nasty > race is clear. > > Why the initial open() would be needed if create(2) always send a Tcreate? Giacomo 2016-11-30 14:53 GMT+01:00 Charles Forsyth <charles.fors...@gmail.com>: > > On 30 November 2016 at 13:32, <cinap_len...@felloff.net> wrote: > >> interesting, the thread starts here: >> >> http://marc.info/?l=9fans&m=111558704718788&w=2 >> > > > I suspect the discussion predated 9P2000 and the introduction of the OEXCL > option. >
