mirror of /home/gitosis/repositories/libev.git
Marc Alexander Lehmann
3 years ago
10 changed files with 861 additions and 91 deletions
@ -0,0 +1,648 @@
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/*
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* libev linux io_uring fd activity backend |
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* |
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* Copyright (c) 2019 Marc Alexander Lehmann <libev@schmorp.de> |
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* All rights reserved. |
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* |
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* Redistribution and use in source and binary forms, with or without modifica- |
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* tion, are permitted provided that the following conditions are met: |
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* |
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* 1. Redistributions of source code must retain the above copyright notice, |
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* this list of conditions and the following disclaimer. |
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* |
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* 2. Redistributions in binary form must reproduce the above copyright |
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* notice, this list of conditions and the following disclaimer in the |
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* documentation and/or other materials provided with the distribution. |
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* |
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED |
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER- |
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* CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO |
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* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE- |
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* CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; |
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* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, |
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH- |
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* ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED |
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* OF THE POSSIBILITY OF SUCH DAMAGE. |
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* |
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* Alternatively, the contents of this file may be used under the terms of |
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* the GNU General Public License ("GPL") version 2 or any later version, |
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* in which case the provisions of the GPL are applicable instead of |
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* the above. If you wish to allow the use of your version of this file |
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* only under the terms of the GPL and not to allow others to use your |
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* version of this file under the BSD license, indicate your decision |
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* by deleting the provisions above and replace them with the notice |
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* and other provisions required by the GPL. If you do not delete the |
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* provisions above, a recipient may use your version of this file under |
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* either the BSD or the GPL. |
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*/ |
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/*
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* general notes about linux io_uring: |
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* |
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* a) it's the best interface I have seen so far. on linux. |
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* b) best is not necessarily very good. |
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* c) it's better than the aio mess, doesn't suffer from the fork problems |
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* of linux aio or epoll and so on and so on. and you could do event stuff |
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* without any syscalls. what's not to like? |
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* d) ok, it's vastly more complex, but that's ok, really. |
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* e) why 3 mmaps instead of one? one would be more space-efficient, |
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* and I can't see what benefit three would have (other than being |
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* somehow resizable/relocatable, but that's apparently not possible). |
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* f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and |
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the bizarre way structure offsets are commuinicated makes it hard to |
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* just print the ring buffer heads, even *iff* the memory were visible |
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* in gdb. but then, that's also ok, really. |
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* g) well, you cannot specify a timeout when waiting for events. no, |
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* seriously, the interface doesn't support a timeout. never seen _that_ |
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* before. sure, you can use a timerfd, but that's another syscall |
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* you could have avoided. overall, this bizarre omission smells |
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* like a µ-optimisation by the io_uring author for his personal |
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* applications, to the detriment of everybody else who just wants |
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* an event loop. but, umm, ok, if that's all, it could be worse. |
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* h) there is a hardcoded limit of 4096 outstanding events. okay, |
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* at least there is no arbitrary low system-wide limit... |
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* i) unlike linux aio, you *can* register more then the limit |
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* of fd events, and the kernel will "gracefully" signal an |
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* overflow, after which you could destroy and recreate the kernel |
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* state, a bit bigger, or fall back to e.g. poll. thats not |
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* totally insane, but kind of questions the point a high |
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* performance I/O framework when it doesn't really work |
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* under stress. |
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* j) but, oh my! is has exactly the same bugs as the linux aio backend, |
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* where some undocumented poll combinations just fail. |
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* so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course, |
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* this is completely undocumented, have I mantioned this already? |
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* k) overall, the *API* itself is, I dare to say, not a total trainwreck. |
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* the big isuess with it are the bugs requiring epoll, which might |
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* or might not get fixed (do I hold my breath?). |
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*/ |
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#include <sys/timerfd.h> |
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#include <sys/mman.h> |
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#include <poll.h> |
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#define IOURING_INIT_ENTRIES 32 |
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/*****************************************************************************/ |
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/* syscall wrapdadoop - this section has the raw api/abi definitions */ |
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#include <linux/fs.h> |
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#include <linux/types.h> |
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/* mostly directly taken from the kernel or documentation */ |
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struct io_uring_sqe |
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{ |
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__u8 opcode; |
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__u8 flags; |
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__u16 ioprio; |
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__s32 fd; |
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__u64 off; |
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__u64 addr; |
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__u32 len; |
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union { |
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__kernel_rwf_t rw_flags; |
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__u32 fsync_flags; |
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__u16 poll_events; |
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__u32 sync_range_flags; |
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__u32 msg_flags; |
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}; |
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__u64 user_data; |
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union { |
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__u16 buf_index; |
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__u64 __pad2[3]; |
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}; |
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}; |
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struct io_uring_cqe |
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{ |
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__u64 user_data; |
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__s32 res; |
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__u32 flags; |
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}; |
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struct io_sqring_offsets |
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{ |
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__u32 head; |
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__u32 tail; |
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__u32 ring_mask; |
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__u32 ring_entries; |
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__u32 flags; |
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__u32 dropped; |
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__u32 array; |
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__u32 resv1; |
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__u64 resv2; |
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}; |
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struct io_cqring_offsets |
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{ |
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__u32 head; |
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__u32 tail; |
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__u32 ring_mask; |
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__u32 ring_entries; |
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__u32 overflow; |
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__u32 cqes; |
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__u64 resv[2]; |
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}; |
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struct io_uring_params |
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{ |
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__u32 sq_entries; |
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__u32 cq_entries; |
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__u32 flags; |
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__u32 sq_thread_cpu; |
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__u32 sq_thread_idle; |
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__u32 resv[5]; |
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struct io_sqring_offsets sq_off; |
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struct io_cqring_offsets cq_off; |
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}; |
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#define IORING_OP_POLL_ADD 6 |
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#define IORING_OP_POLL_REMOVE 7 |
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#define IORING_ENTER_GETEVENTS 0x01 |
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#define IORING_OFF_SQ_RING 0x00000000ULL |
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#define IORING_OFF_CQ_RING 0x08000000ULL |
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#define IORING_OFF_SQES 0x10000000ULL |
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inline_size |
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int |
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evsys_io_uring_setup (unsigned entries, struct io_uring_params *params) |
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{ |
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return ev_syscall2 (SYS_io_uring_setup, entries, params); |
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} |
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inline_size |
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int |
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evsys_io_uring_enter (int fd, unsigned to_submit, unsigned min_complete, unsigned flags, const sigset_t *sig, size_t sigsz) |
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{ |
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return ev_syscall6 (SYS_io_uring_enter, fd, to_submit, min_complete, flags, sig, sigsz); |
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} |
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/*****************************************************************************/ |
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/* actual backed implementation */ |
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/* we hope that volatile will make the compiler access this variables only once */ |
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#define EV_SQ_VAR(name) *(volatile unsigned *)((char *)iouring_sq_ring + iouring_sq_ ## name) |
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#define EV_CQ_VAR(name) *(volatile unsigned *)((char *)iouring_cq_ring + iouring_cq_ ## name) |
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/* the index array */ |
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#define EV_SQ_ARRAY ((unsigned *)((char *)iouring_sq_ring + iouring_sq_array)) |
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/* the submit/completion queue entries */ |
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#define EV_SQES ((struct io_uring_sqe *) iouring_sqes) |
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#define EV_CQES ((struct io_uring_cqe *)((char *)iouring_cq_ring + iouring_cq_cqes)) |
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static |
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struct io_uring_sqe * |
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iouring_sqe_get (EV_P) |
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{ |
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unsigned tail = EV_SQ_VAR (tail); |
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if (tail + 1 - EV_SQ_VAR (head) > EV_SQ_VAR (ring_entries)) |
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{ |
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/* queue full, flush */ |
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evsys_io_uring_enter (iouring_fd, iouring_to_submit, 0, 0, 0, 0); |
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iouring_to_submit = 0; |
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} |
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assert (("libev: io_uring queue full after flush", tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries))); |
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return EV_SQES + (tail & EV_SQ_VAR (ring_mask)); |
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} |
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inline_size |
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struct io_uring_sqe * |
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iouring_sqe_submit (EV_P_ struct io_uring_sqe *sqe) |
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{ |
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unsigned idx = sqe - EV_SQES; |
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EV_SQ_ARRAY [idx] = idx; |
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ECB_MEMORY_FENCE_RELEASE; |
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++EV_SQ_VAR (tail); |
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/*ECB_MEMORY_FENCE_RELEASE; /* for the time being we assume this is not needed */ |
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++iouring_to_submit; |
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} |
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/*****************************************************************************/ |
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/* when the timerfd expires we simply note the fact,
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* as the purpose of the timerfd is to wake us up, nothing else. |
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* the next iteration should re-set it. |
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*/ |
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static void |
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iouring_tfd_cb (EV_P_ struct ev_io *w, int revents) |
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{ |
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iouring_tfd_to = EV_TSTAMP_HUGE; |
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} |
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static void |
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iouring_epoll_cb (EV_P_ struct ev_io *w, int revents) |
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{ |
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epoll_poll (EV_A_ 0); |
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} |
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/* called for full and partial cleanup */ |
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ecb_cold |
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static int |
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iouring_internal_destroy (EV_P) |
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{ |
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close (iouring_tfd); |
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close (iouring_fd); |
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if (iouring_sq_ring != MAP_FAILED) munmap (iouring_sq_ring, iouring_sq_ring_size); |
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if (iouring_cq_ring != MAP_FAILED) munmap (iouring_cq_ring, iouring_cq_ring_size); |
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if (iouring_sqes != MAP_FAILED) munmap (iouring_sqes , iouring_sqes_size ); |
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if (ev_is_active (&iouring_epoll_w)) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_epoll_w); |
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if (ev_is_active (&iouring_tfd_w )) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_tfd_w ); |
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} |
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ecb_cold |
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static int |
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iouring_internal_init (EV_P) |
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{ |
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struct io_uring_params params = { 0 }; |
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iouring_to_submit = 0; |
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iouring_tfd = -1; |
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iouring_sq_ring = MAP_FAILED; |
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iouring_cq_ring = MAP_FAILED; |
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iouring_sqes = MAP_FAILED; |
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for (;;) |
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{ |
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iouring_fd = evsys_io_uring_setup (iouring_entries, ¶ms); |
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if (iouring_fd >= 0) |
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break; /* yippie */ |
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if (errno != EINVAL) |
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return -1; /* we failed */ |
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/* EINVAL: lots of possible reasons, but maybe
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* it is because we hit the unqueryable hardcoded size limit |
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*/ |
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/* we hit the limit already, give up */ |
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if (iouring_max_entries) |
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return -1; |
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/* first time we hit EINVAL? assume we hit the limit, so go back and retry */ |
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iouring_entries >>= 1; |
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iouring_max_entries = iouring_entries; |
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} |
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iouring_sq_ring_size = params.sq_off.array + params.sq_entries * sizeof (unsigned); |
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iouring_cq_ring_size = params.cq_off.cqes + params.cq_entries * sizeof (struct io_uring_cqe); |
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iouring_sqes_size = params.sq_entries * sizeof (struct io_uring_sqe); |
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iouring_sq_ring = mmap (0, iouring_sq_ring_size, PROT_READ | PROT_WRITE, |
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MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQ_RING); |
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iouring_cq_ring = mmap (0, iouring_cq_ring_size, PROT_READ | PROT_WRITE, |
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MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_CQ_RING); |
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iouring_sqes = mmap (0, iouring_sqes_size, PROT_READ | PROT_WRITE, |
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MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQES); |
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if (iouring_sq_ring == MAP_FAILED || iouring_cq_ring == MAP_FAILED || iouring_sqes == MAP_FAILED) |
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return -1; |
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iouring_sq_head = params.sq_off.head; |
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iouring_sq_tail = params.sq_off.tail; |
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iouring_sq_ring_mask = params.sq_off.ring_mask; |
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iouring_sq_ring_entries = params.sq_off.ring_entries; |
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iouring_sq_flags = params.sq_off.flags; |
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iouring_sq_dropped = params.sq_off.dropped; |
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iouring_sq_array = params.sq_off.array; |
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iouring_cq_head = params.cq_off.head; |
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iouring_cq_tail = params.cq_off.tail; |
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iouring_cq_ring_mask = params.cq_off.ring_mask; |
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iouring_cq_ring_entries = params.cq_off.ring_entries; |
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iouring_cq_overflow = params.cq_off.overflow; |
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iouring_cq_cqes = params.cq_off.cqes; |
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iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC); |
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if (iouring_tfd < 0) |
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return iouring_tfd; |
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iouring_tfd_to = EV_TSTAMP_HUGE; |
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return 0; |
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} |
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ecb_cold |
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static void |
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iouring_fork (EV_P) |
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{ |
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iouring_internal_destroy (EV_A); |
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while (iouring_internal_init (EV_A) < 0) |
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ev_syserr ("(libev) io_uring_setup"); |
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/* forking epoll should also effectively unregister all fds from the backend */ |
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epoll_fork (EV_A); |
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/* epoll_fork already did this. hopefully */ |
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/*fd_rearm_all (EV_A);*/ |
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ev_io_stop (EV_A_ &iouring_epoll_w); |
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ev_io_set (EV_A_ &iouring_epoll_w, backend_fd, EV_READ); |
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ev_io_start (EV_A_ &iouring_epoll_w); |
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ev_io_stop (EV_A_ &iouring_tfd_w); |
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ev_io_set (EV_A_ &iouring_tfd_w, iouring_tfd, EV_READ); |
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ev_io_start (EV_A_ &iouring_tfd_w); |
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} |
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/*****************************************************************************/ |
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static void |
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iouring_modify (EV_P_ int fd, int oev, int nev) |
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{ |
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fprintf (stderr,"modify %d (%d, %d) %d\n", fd, oev,nev, anfds[fd].eflags);//D
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if (ecb_expect_false (anfds [fd].eflags)) |
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{ |
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/* we handed this fd over to epoll, so undo this first */ |
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/* we do it manually because the optimisations on epoll_modify won't do us any good */ |
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epoll_ctl (iouring_fd, EPOLL_CTL_DEL, fd, 0); |
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anfds [fd].eflags = 0; |
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oev = 0; |
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} |
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if (oev) |
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{ |
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/* we assume the sqe's are all "properly" initialised */ |
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struct io_uring_sqe *sqe = iouring_sqe_get (EV_A); |
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sqe->opcode = IORING_OP_POLL_REMOVE; |
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sqe->fd = fd; |
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sqe->user_data = -1; |
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iouring_sqe_submit (EV_A_ sqe); |
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} |
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/* increment generation counter to avoid handling old events */ |
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++anfds [fd].egen; |
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if (nev) |
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{ |
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struct io_uring_sqe *sqe = iouring_sqe_get (EV_A); |
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sqe->opcode = IORING_OP_POLL_ADD; |
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sqe->fd = fd; |
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sqe->user_data = (uint32_t)fd | ((__u64)anfds [fd].egen << 32); |
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sqe->poll_events = |
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(nev & EV_READ ? POLLIN : 0) |
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| (nev & EV_WRITE ? POLLOUT : 0); |
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iouring_sqe_submit (EV_A_ sqe); |
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} |
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} |
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inline_size |
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void |
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iouring_tfd_update (EV_P_ ev_tstamp timeout) |
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{ |
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ev_tstamp tfd_to = mn_now + timeout; |
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/* we assume there will be many iterations per timer change, so
|
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* we only re-set the timerfd when we have to because its expiry |
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* is too late. |
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*/ |
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if (ecb_expect_false (tfd_to < iouring_tfd_to)) |
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{ |
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struct itimerspec its; |
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iouring_tfd_to = tfd_to; |
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EV_TS_SET (its.it_interval, 0.); |
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EV_TS_SET (its.it_value, tfd_to); |
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if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0) |
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assert (("libev: iouring timerfd_settime failed", 0)); |
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} |
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} |
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inline_size |
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void |
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iouring_process_cqe (EV_P_ struct io_uring_cqe *cqe) |
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{ |
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int fd = cqe->user_data & 0xffffffffU; |
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uint32_t gen = cqe->user_data >> 32; |
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int res = cqe->res; |
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/* ignore fd removal events, if there are any. TODO: verify */ |
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if (cqe->user_data == (__u64)-1) |
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abort ();//D
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assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax)); |
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/* documentation lies, of course. the result value is NOT like
|
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* normal syscalls, but like linux raw syscalls, i.e. negative |
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* error numbers. fortunate, as otherwise there would be no way |
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* to get error codes at all. still, why not document this? |
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*/ |
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|
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/* ignore event if generation doesn't match */ |
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/* this should actually be very rare */ |
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if (ecb_expect_false ((uint32_t)anfds [fd].egen != gen)) |
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return; |
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if (ecb_expect_false (res < 0)) |
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{ |
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if (res == -EINVAL) |
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{ |
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/* we assume this error code means the fd/poll combination is buggy
|
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* and fall back to epoll. |
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* this error code might also indicate a bug, but the kernel doesn't |
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* distinguish between those two conditions, so... sigh... |
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*/ |
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|
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epoll_modify (EV_A_ fd, 0, anfds [fd].events); |
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} |
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else if (res == -EBADF) |
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{ |
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assert (("libev: event loop rejected bad fd", res != -EBADF)); |
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fd_kill (EV_A_ fd); |
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} |
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else |
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{ |
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errno = -res; |
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ev_syserr ("(libev) IORING_OP_POLL_ADD"); |
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} |
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|
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return; |
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} |
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fprintf (stderr, "fd %d event, rearm\n", fd);//D
|
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|
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/* feed events, we do not expect or handle POLLNVAL */ |
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fd_event ( |
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EV_A_ |
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fd, |
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(res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0) |
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| (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0) |
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); |
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|
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/* io_uring is oneshot, so we need to re-arm the fd next iteration */ |
||||
/* this also means we usually have to do at least one syscall per iteration */ |
||||
anfds [fd].events = 0; |
||||
fd_change (EV_A_ fd, EV_ANFD_REIFY); |
||||
} |
||||
|
||||
/* called when the event queue overflows */ |
||||
ecb_cold |
||||
static void |
||||
iouring_overflow (EV_P) |
||||
{ |
||||
/* we have two options, resize the queue (by tearing down
|
||||
* everything and recreating it, or living with it |
||||
* and polling. |
||||
* we implement this by resizing tghe queue, and, if that fails, |
||||
* we just recreate the state on every failure, which |
||||
* kind of is a very inefficient poll. |
||||
* one danger is, due to the bios toward lower fds, |
||||
* we will only really get events for those, so |
||||
* maybe we need a poll() fallback, after all. |
||||
*/ |
||||
/*EV_CQ_VAR (overflow) = 0;*/ /* need to do this if we keep the state and poll manually */ |
||||
|
||||
fd_rearm_all (EV_A); |
||||
|
||||
/* we double the size until we hit the hard-to-probe maximum */ |
||||
if (!iouring_max_entries) |
||||
{ |
||||
iouring_entries <<= 1; |
||||
iouring_fork (EV_A); |
||||
} |
||||
else |
||||
{ |
||||
/* we hit the kernel limit, we should fall back to something else.
|
||||
* we can either poll() a few times and hope for the best, |
||||
* poll always, or switch to epoll. |
||||
* since we use epoll anyways, go epoll. |
||||
*/ |
||||
|
||||
iouring_internal_destroy (EV_A); |
||||
|
||||
/* this should make it so that on return, we don'T call any uring functions */ |
||||
iouring_to_submit = 0; |
||||
|
||||
for (;;) |
||||
{ |
||||
backend = epoll_init (EV_A_ 0); |
||||
|
||||
if (backend) |
||||
break; |
||||
|
||||
ev_syserr ("(libev) iouring switch to epoll"); |
||||
} |
||||
} |
||||
} |
||||
|
||||
/* handle any events in the completion queue, return true if there were any */ |
||||
static int |
||||
iouring_handle_cq (EV_P) |
||||
{ |
||||
unsigned head, tail, mask; |
||||
|
||||
head = EV_CQ_VAR (head); |
||||
ECB_MEMORY_FENCE_ACQUIRE; |
||||
tail = EV_CQ_VAR (tail); |
||||
|
||||
if (head == tail) |
||||
return 0; |
||||
|
||||
/* it can only overflow if we have events, yes, yes? */ |
||||
if (ecb_expect_false (EV_CQ_VAR (overflow))) |
||||
{ |
||||
iouring_overflow (EV_A); |
||||
return 1; |
||||
} |
||||
|
||||
mask = EV_CQ_VAR (ring_mask); |
||||
|
||||
do |
||||
iouring_process_cqe (EV_A_ &EV_CQES [head++ & mask]); |
||||
while (head != tail); |
||||
|
||||
EV_CQ_VAR (head) = head; |
||||
ECB_MEMORY_FENCE_RELEASE; |
||||
|
||||
return 1; |
||||
} |
||||
|
||||
static void |
||||
iouring_poll (EV_P_ ev_tstamp timeout) |
||||
{ |
||||
/* if we have events, no need for extra syscalls, but we might have to queue events */ |
||||
if (iouring_handle_cq (EV_A)) |
||||
timeout = 0.; |
||||
else |
||||
/* no events, so maybe wait for some */ |
||||
iouring_tfd_update (EV_A_ timeout); |
||||
|
||||
/* only enter the kernel if we have somethign to submit, or we need to wait */ |
||||
if (timeout || iouring_to_submit) |
||||
{ |
||||
int res; |
||||
|
||||
EV_RELEASE_CB; |
||||
|
||||
res = evsys_io_uring_enter (iouring_fd, iouring_to_submit, 1, |
||||
timeout ? IORING_ENTER_GETEVENTS : 0, 0, 0); |
||||
iouring_to_submit = 0; |
||||
|
||||
EV_ACQUIRE_CB; |
||||
|
||||
if (ecb_expect_false (res < 0)) |
||||
if (errno == EINTR) |
||||
/* ignore */; |
||||
else |
||||
ev_syserr ("(libev) iouring setup"); |
||||
else |
||||
iouring_handle_cq (EV_A); |
||||
} |
||||
} |
||||
|
||||
inline_size |
||||
int |
||||
iouring_init (EV_P_ int flags) |
||||
{ |
||||
if (!epoll_init (EV_A_ 0)) |
||||
return 0; |
||||
|
||||
ev_io_init (EV_A_ &iouring_epoll_w, iouring_epoll_cb, backend_fd, EV_READ); |
||||
ev_set_priority (&iouring_epoll_w, EV_MAXPRI); |
||||
|
||||
ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ); |
||||
ev_set_priority (&iouring_tfd_w, EV_MAXPRI); |
||||
|
||||
iouring_entries = IOURING_INIT_ENTRIES; |
||||
iouring_max_entries = 0; |
||||
|
||||
if (iouring_internal_init (EV_A) < 0) |
||||
{ |
||||
iouring_internal_destroy (EV_A); |
||||
return 0; |
||||
} |
||||
|
||||
ev_io_start (EV_A_ &iouring_epoll_w); |
||||
ev_unref (EV_A); /* watcher should not keep loop alive */ |
||||
|
||||
ev_io_start (EV_A_ &iouring_tfd_w); |
||||
ev_unref (EV_A); /* watcher should not keep loop alive */ |
||||
|
||||
backend_modify = iouring_modify; |
||||
backend_poll = iouring_poll; |
||||
|
||||
return EVBACKEND_IOURING; |
||||
} |
||||
|
||||
inline_size |
||||
void |
||||
iouring_destroy (EV_P) |
||||
{ |
||||
iouring_internal_destroy (EV_A); |
||||
epoll_destroy (EV_A); |
||||
} |
||||
|
||||
Loading…
Reference in new issue