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For existing epoll event loops that can't fully convert to io_uring,
the used approach is usually to add the io_uring fd to the epoll
instance and use epoll_wait() to wait on both "legacy" and io_uring
events. While this work, it isn't optimal as:
1) epoll_wait() is pretty limited in what it can do. It does not support
partial reaping of events, or waiting on a batch of events.
2) When an io_uring ring is added to an epoll instance, it activates the
io_uring "I'm being polled" logic which slows things down.
Rather than use this approach, with EPOLL_WAIT support added to io_uring,
event loops can use the normal io_uring wait logic for everything, as
long as an epoll wait request has been armed with io_uring.
Note that IORING_OP_EPOLL_WAIT does NOT take a timeout value, as this
is an async request. Waiting on io_uring events in general has various
timeout parameters, and those are the ones that should be used when
waiting on any kind of request. If events are immediately available for
reaping, then This opcode will return those immediately. If none are
available, then it will post an async completion when they become
available.
cqe->res will contain either an error code (< 0 value) for a malformed
request, invalid epoll instance, etc. It will return a positive result
indicating how many events were reaped.
IORING_OP_EPOLL_WAIT requests may be canceled using the normal io_uring
cancelation infrastructure.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Just have the Makefile add the object if epoll is enabled, then it's
not necessary to guard the entire epoll.c file inside an CONFIG_EPOLL
ifdef.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Libuv recently started using it so there is at least one consumer now.
Cc: stable@vger.kernel.org
Fixes: 61a2732af4b0 ("io_uring: deprecate epoll_ctl support")
Link: https://github.com/libuv/libuv/pull/3979
Signed-off-by: Ben Noordhuis <info@bnoordhuis.nl>
Link: https://lore.kernel.org/r/20230506095502.13401-1-info@bnoordhuis.nl
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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We need to make sure (at build time) that struct io_cmd_data is not
casted to a structure that's larger.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Link: https://lore.kernel.org/r/c024cdf25ae19fc0319d4180e2298bade8ed17b8.1660201408.git.metze@samba.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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io_uring/io_uring.h already includes io_uring_types.h, no need to
include it every time. Kill it in a bunch of places, it prepares us for
following patches.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/94d8c943fbe0ef949981c508ddcee7fc1c18850f.1655384063.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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As far as we know, nobody ever adopted the epoll_ctl management via
io_uring. Deprecate it now with a warning, and plan on removing it in
a later kernel version. When we do remove it, we can revert the following
commits as well:
39220e8d4a2a ("eventpoll: support non-blocking do_epoll_ctl() calls")
58e41a44c488 ("eventpoll: abstract out epoll_ctl() handler")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/io-uring/CAHk-=wiTyisXBgKnVHAGYCNvkmjk=50agS2Uk6nr+n3ssLZg2w@mail.gmail.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Would be nice to sort out Kconfig for this and don't even compile
epoll.c if we don't have epoll configured.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Jens Axboe
Ben Noordhuis
Stefan Metzmacher
Pavel Begunkov