Hi, This adds support for just doing the RCU based (and non-blocking) part of path resolution. The main motivation is for io_uring to be able to do saner/faster open, so we don't always have to go async, particularly for the fast path of the data already being cached. Internally that is presented as LOOKUP_NONBLOCK, which depends on LOOKUP_RCU for doing the right thing. If we terminate the RCU part of the lookup, then we return -EAGAIN if LOOKUP_NONBLOCK is also set. The second patch is enabling this through openat2() as well, by adding a RESOLVE_NONBLOCK that can be passed in struct open_how ->resolve as well. Basic test case: [root@archlinux liburing]# echo 3 > /proc/sys/vm/drop_caches [root@archlinux liburing]# test/do-open2 /etc/nanorc open: -1 openat2: Resource temporarily unavailable [root@archlinux liburing]# touch /etc/nanorc [root@archlinux liburing]# test/do-open2 /etc/nanorc open: 3 -- Jens Axboe
