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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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/* |
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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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* (FIXME: newer kernels can use 2 mmaps only, need to look into this). |
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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 communicated 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 ยต-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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* (FIXME: jens mentioned timeout commands, need to investigate) |
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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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* (FIXME: apparently, this was increased to 32768 in later kernels( |
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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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* (FIXME: iouring should no longer drop events, need to investigate) |
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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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|
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/* TODO: use internal TIMEOUT */ |
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/* TODO: take advantage of single mmap, NODROP etc. */ |
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/* TODO: resize cq/sq size independently */ |
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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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|
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#define IOURING_INIT_ENTRIES 32 |
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|
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/*****************************************************************************/ |
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/* syscall wrapdadoop - this section has the raw api/abi definitions */ |
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|
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#include <linux/fs.h> |
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#include <linux/types.h> |
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|
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/* mostly directly taken from the kernel or documentation */ |
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|
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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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union { |
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__u64 off; |
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__u64 addr2; |
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}; |
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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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__u32 timeout_flags; |
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__u32 accept_flags; |
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__u32 cancel_flags; |
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__u32 open_flags; |
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__u32 statx_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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|
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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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|
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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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|
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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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|
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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 features; |
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__u32 resv[4]; |
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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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|
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#define IORING_OP_POLL_ADD 6 |
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#define IORING_OP_POLL_REMOVE 7 |
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|
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#define IORING_ENTER_GETEVENTS 0x01 |
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|
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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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|
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#define IORING_FEAT_SINGLE_MMAP 0x1 |
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#define IORING_FEAT_NODROP 0x2 |
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#define IORING_FEAT_SUBMIT_STABLE 0x4 |
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|
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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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|
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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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/*****************************************************************************/ |
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/* actual backed implementation */ |
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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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return EV_SQES + (tail & EV_SQ_VAR (ring_mask)); |
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} |
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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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|
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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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/*****************************************************************************/ |
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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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|
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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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|
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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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|
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if (ev_is_active (&iouring_tfd_w)) |
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{ |
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ev_ref (EV_A); |
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ev_io_stop (EV_A_ &iouring_tfd_w); |
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} |
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} |
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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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|
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iouring_to_submit = 0; |
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|
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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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|
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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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|
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if (iouring_fd >= 0) |
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break; /* yippie */ |
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|
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if (errno != EINVAL) |
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return -1; /* we failed */ |
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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC); |
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|
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if (iouring_tfd < 0) |
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return iouring_tfd; |
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|
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iouring_tfd_to = EV_TSTAMP_HUGE; |
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|
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return 0; |
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} |
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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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|
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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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|
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fd_rearm_all (EV_A); |
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|
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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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/*****************************************************************************/ |
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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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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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} |
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|
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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)(uint32_t)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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|
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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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|
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/* we assume there will be many iterations per timer change, so |
410 |
* we only re-set the timerfd when we have to because its expiry |
411 |
* 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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|
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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); |
420 |
|
421 |
if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0) |
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assert (("libev: iouring timerfd_settime failed", 0)); |
423 |
} |
424 |
} |
425 |
|
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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) |
429 |
{ |
430 |
int fd = cqe->user_data & 0xffffffffU; |
431 |
uint32_t gen = cqe->user_data >> 32; |
432 |
int res = cqe->res; |
433 |
|
434 |
/* ignore fd removal events, if there are any. TODO: verify */ |
435 |
/* TODO: yes, this triggers */ |
436 |
if (cqe->user_data == (__u64)-1) |
437 |
return; |
438 |
|
439 |
assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax)); |
440 |
|
441 |
/* documentation lies, of course. the result value is NOT like |
442 |
* normal syscalls, but like linux raw syscalls, i.e. negative |
443 |
* error numbers. fortunate, as otherwise there would be no way |
444 |
* to get error codes at all. still, why not document this? |
445 |
*/ |
446 |
|
447 |
/* ignore event if generation doesn't match */ |
448 |
/* this should actually be very rare */ |
449 |
if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen)) |
450 |
return; |
451 |
|
452 |
if (ecb_expect_false (res < 0)) |
453 |
{ |
454 |
//TODO: EINVAL handling (was something failed with this fd) |
455 |
//TODO: EBUSY happens when? |
456 |
|
457 |
if (res == -EBADF) |
458 |
{ |
459 |
assert (("libev: event loop rejected bad fd", res != -EBADF)); |
460 |
fd_kill (EV_A_ fd); |
461 |
} |
462 |
else |
463 |
{ |
464 |
errno = -res; |
465 |
ev_syserr ("(libev) IORING_OP_POLL_ADD"); |
466 |
} |
467 |
|
468 |
return; |
469 |
} |
470 |
|
471 |
/* feed events, we do not expect or handle POLLNVAL */ |
472 |
fd_event ( |
473 |
EV_A_ |
474 |
fd, |
475 |
(res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0) |
476 |
| (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0) |
477 |
); |
478 |
|
479 |
/* io_uring is oneshot, so we need to re-arm the fd next iteration */ |
480 |
/* this also means we usually have to do at least one syscall per iteration */ |
481 |
anfds [fd].events = 0; |
482 |
fd_change (EV_A_ fd, EV_ANFD_REIFY); |
483 |
} |
484 |
|
485 |
/* called when the event queue overflows */ |
486 |
ecb_cold |
487 |
static void |
488 |
iouring_overflow (EV_P) |
489 |
{ |
490 |
/* we have two options, resize the queue (by tearing down |
491 |
* everything and recreating it, or living with it |
492 |
* and polling. |
493 |
* we implement this by resizing the queue, and, if that fails, |
494 |
* we just recreate the state on every failure, which |
495 |
* kind of is a very inefficient poll. |
496 |
* one danger is, due to the bios toward lower fds, |
497 |
* we will only really get events for those, so |
498 |
* maybe we need a poll() fallback, after all. |
499 |
*/ |
500 |
/*EV_CQ_VAR (overflow) = 0;*/ /* need to do this if we keep the state and poll manually */ |
501 |
|
502 |
fd_rearm_all (EV_A); |
503 |
|
504 |
/* we double the size until we hit the hard-to-probe maximum */ |
505 |
if (!iouring_max_entries) |
506 |
{ |
507 |
iouring_entries <<= 1; |
508 |
iouring_fork (EV_A); |
509 |
} |
510 |
else |
511 |
{ |
512 |
/* we hit the kernel limit, we should fall back to something else. |
513 |
* we can either poll() a few times and hope for the best, |
514 |
* poll always, or switch to epoll. |
515 |
* TODO: is this necessary with newer kernels? |
516 |
*/ |
517 |
|
518 |
iouring_internal_destroy (EV_A); |
519 |
|
520 |
/* this should make it so that on return, we don't call any uring functions */ |
521 |
iouring_to_submit = 0; |
522 |
|
523 |
for (;;) |
524 |
{ |
525 |
backend = epoll_init (EV_A_ 0); |
526 |
|
527 |
if (backend) |
528 |
break; |
529 |
|
530 |
ev_syserr ("(libev) iouring switch to epoll"); |
531 |
} |
532 |
} |
533 |
} |
534 |
|
535 |
/* handle any events in the completion queue, return true if there were any */ |
536 |
static int |
537 |
iouring_handle_cq (EV_P) |
538 |
{ |
539 |
unsigned head, tail, mask; |
540 |
|
541 |
head = EV_CQ_VAR (head); |
542 |
ECB_MEMORY_FENCE_ACQUIRE; |
543 |
tail = EV_CQ_VAR (tail); |
544 |
|
545 |
if (head == tail) |
546 |
return 0; |
547 |
|
548 |
/* it can only overflow if we have events, yes, yes? */ |
549 |
if (ecb_expect_false (EV_CQ_VAR (overflow))) |
550 |
{ |
551 |
iouring_overflow (EV_A); |
552 |
return 1; |
553 |
} |
554 |
|
555 |
mask = EV_CQ_VAR (ring_mask); |
556 |
|
557 |
do |
558 |
iouring_process_cqe (EV_A_ &EV_CQES [head++ & mask]); |
559 |
while (head != tail); |
560 |
|
561 |
EV_CQ_VAR (head) = head; |
562 |
ECB_MEMORY_FENCE_RELEASE; |
563 |
|
564 |
return 1; |
565 |
} |
566 |
|
567 |
static void |
568 |
iouring_poll (EV_P_ ev_tstamp timeout) |
569 |
{ |
570 |
/* if we have events, no need for extra syscalls, but we might have to queue events */ |
571 |
if (iouring_handle_cq (EV_A)) |
572 |
timeout = EV_TS_CONST (0.); |
573 |
else |
574 |
/* no events, so maybe wait for some */ |
575 |
iouring_tfd_update (EV_A_ timeout); |
576 |
|
577 |
/* only enter the kernel if we have something to submit, or we need to wait */ |
578 |
if (timeout || iouring_to_submit) |
579 |
{ |
580 |
int res; |
581 |
|
582 |
EV_RELEASE_CB; |
583 |
|
584 |
res = evsys_io_uring_enter (iouring_fd, iouring_to_submit, 1, |
585 |
timeout > EV_TS_CONST (0.) ? IORING_ENTER_GETEVENTS : 0, 0, 0); |
586 |
iouring_to_submit = 0; |
587 |
|
588 |
EV_ACQUIRE_CB; |
589 |
|
590 |
if (ecb_expect_false (res < 0)) |
591 |
if (errno == EINTR) |
592 |
/* ignore */; |
593 |
else |
594 |
ev_syserr ("(libev) iouring setup"); |
595 |
else |
596 |
iouring_handle_cq (EV_A); |
597 |
} |
598 |
} |
599 |
|
600 |
inline_size |
601 |
int |
602 |
iouring_init (EV_P_ int flags) |
603 |
{ |
604 |
iouring_entries = IOURING_INIT_ENTRIES; |
605 |
iouring_max_entries = 0; |
606 |
|
607 |
if (iouring_internal_init (EV_A) < 0) |
608 |
{ |
609 |
iouring_internal_destroy (EV_A); |
610 |
return 0; |
611 |
} |
612 |
|
613 |
ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ); |
614 |
ev_set_priority (&iouring_tfd_w, EV_MINPRI); |
615 |
ev_io_start (EV_A_ &iouring_tfd_w); |
616 |
ev_unref (EV_A); /* watcher should not keep loop alive */ |
617 |
|
618 |
backend_modify = iouring_modify; |
619 |
backend_poll = iouring_poll; |
620 |
|
621 |
return EVBACKEND_IOURING; |
622 |
} |
623 |
|
624 |
inline_size |
625 |
void |
626 |
iouring_destroy (EV_P) |
627 |
{ |
628 |
iouring_internal_destroy (EV_A); |
629 |
} |
630 |
|