On Fri, Aug 15, 2025 at 1:50 AM Thomas Bertschinger <tahbertschinger@xxxxxxxxx> wrote: > > This series adds support for name_to_handle_at() and open_by_handle_at() > to io_uring. The idea is for these opcodes to be useful for userspace > NFS servers that want to use io_uring. > > name_to_handle_at() > =================== > > Support for name_to_handle_at() is added in patches 1 and 2. > > In order to do a non-blocking name_to_handle_at(), a new helper > do_name_to_handle_at() is created that takes a lookup_flags argument. > > This is to support non-blocking lookup when called with > IO_URING_F_NONBLOCK--user_path_at() will be called with LOOKUP_CACHED > in that case. > > Aside from the lookup, I don't think there is anything else that > do_name_to_handle_at() does that would be a problem in the non-blocking > case. There is a GFP_KERNEL allocation: > > do_name_to_handle_at() > -> do_path_to_handle() > -> kzalloc(..., GFP_KERNEL) > > But I think that's OK? Let me know if there's anything else I'm > missing... > > open_by_handle_at() > =================== > > Patch 3 is a fixup to fhandle.c:do_handle_open() that (I believe) fixes > a bug and can exist independently of this series, but it fits in with > these changes so I'm including it here. > > Support for open_by_handle_at() is added in patches 4 - 6. > > A helper __do_handle_open() is created that does the file open without > installing a file descriptor for it. This is needed because io_uring > needs to decide between using a file descriptor or a fixed file. > > No attempt is made to support a non-blocking open_by_handle_at()--the > attempt is always immediately returned with -EAGAIN if > IO_URING_F_NONBLOCK is set. > > This isn't ideal and it would be nice to add support for non-blocking > open by handle in the future. This would presumably require updates to > the ->encode_fh() implementation for filesystems that want to > support this. Correction: ->encode_fh() is for name_to_handle() You want to say that ->fh_to_dentry() need to support cached lookup, but FWIW, the blocking code is more likely to come from the lookup in exportfs_decode_fh_raw() => ... reconnect_one() not from the filesystem code. The fs would "only" need to be taught to return an alias to a cached inode and generic code would "only" need to be taught to give up on a disconnected dir dentry. Doesn't sound too hard (famous last words). Thanks, Amir. > > I see that lack of support for non-blocking operation was a dealbreaker > for adding getdents to io_uring previously: > > https://lore.kernel.org/io-uring/20230428050640.GA1969623@xxxxxxxxxxxxxxxxxxx/ > > On the other hand, AFAICT, support for openat() was originally added in > 15b71abe7b52 (io_uring: add support for IORING_OP_OPENAT) without a non- > blocking lookup, and the possibility of non-blocking lookup later added > in 3a81fd02045c (io_uring: enable LOOKUP_CACHED path resolution for > filename lookups). > > (To be honest I'm a little confused by the history here. The commit > message of 15b71abe7b52 says > > > For the normal case of a non-blocking path lookup this will complete > > inline. If we have to do IO to perform the open, it'll be done from > > async context. > > but from the commit contents this would NOT appear to be the case: > > > + if (force_nonblock) { > > + req->work.flags |= IO_WQ_WORK_NEEDS_FILES; > > + return -EAGAIN; > > + } > > until the support is really added in the later commit. Am I confused or > is the commit message wrong?) > > In any event, based on my reading of the history, it would appear to be > OK to add open_by_handle_at() initially without support for inline > completion, and then later add that when the filesystem implementations > can be updated to support this. > > Please let me know if I am wrong on my interpretation of the history or > if anyone disagrees with the conclusion. > > Testing > ======= > > A liburing branch that includes support for the new opcodes, as well as > a test, is available at: > > https://github.com/bertschingert/liburing/tree/open_by_handle_at > > To run the test: > > $ ./test/open_by_handle_at.t > > Thomas Bertschinger (6): > fhandle: create helper for name_to_handle_at(2) > io_uring: add support for IORING_OP_NAME_TO_HANDLE_AT > fhandle: do_handle_open() should get FD with user flags > fhandle: create __do_handle_open() helper > io_uring: add __io_open_prep() helper > io_uring: add support for IORING_OP_OPEN_BY_HANDLE_AT > > fs/fhandle.c | 85 ++++++++++++--------- > fs/internal.h | 9 +++ > include/uapi/linux/io_uring.h | 2 + > io_uring/opdef.c | 14 ++++ > io_uring/openclose.c | 137 +++++++++++++++++++++++++++++++--- > io_uring/openclose.h | 5 ++ > 6 files changed, 209 insertions(+), 43 deletions(-) > > -- > 2.50.1 > >
