| 1 | /*
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| 2 | This is a simple "eventfd" example that uses io_uring
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| 3 | It demonstrates that reads work as expected on eventfds.
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| 4 | It uses liburing for simplicity.
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| 5 | */
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| 6 |
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| 7 |
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| 8 | #ifndef _GNU_SOURCE
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| 9 | #define _GNU_SOURCE
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| 10 | #endif
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| 11 |
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| 12 | #include <fcntl.h>
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| 13 | #include <liburing.h>
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| 14 | #include <stdio.h>
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| 15 | #include <string.h>
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| 16 | #include <unistd.h>
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| 17 | #include <sys/eventfd.h>
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| 18 |
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| 19 | struct io_uring ring;
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| 20 |
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| 21 |
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| 22 | int main(int argc, char * argv[]) {
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| 23 | int fd = eventfd(0, 0);
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| 24 | if(fd < 0) {
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| 25 | printf("Could not open event fd.\n");
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| 26 | return 2;
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| 27 | }
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| 28 |
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| 29 | /* prep the array */
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| 30 | char buf[sizeof(uint64_t)] = { 0 };
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| 31 | struct iovec iov = { buf, 8 };
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| 32 |
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| 33 | {
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| 34 | /* Do one write so we can compare blocking behaviour */
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| 35 | eventfd_t val;
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| 36 | val = 1;
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| 37 | eventfd_write( fd, val );
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| 38 | }
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| 39 |
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| 40 | /* init liburing */
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| 41 | io_uring_queue_init(256, &ring, 0);
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| 42 |
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| 43 | /* declare required structs */
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| 44 | struct io_uring_sqe * sqe;
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| 45 | struct io_uring_cqe * cqe;
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| 46 |
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| 47 | /* get an sqe and fill in a READ operation */
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| 48 | sqe = io_uring_get_sqe(&ring);
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| 49 | io_uring_prep_read(sqe, fd, buf, 8, 0);
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| 50 |
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| 51 | sqe->user_data = fd;
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| 52 |
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| 53 | /* tell the kernel we have an sqe ready for consumption */
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| 54 | io_uring_submit(&ring);
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| 55 |
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| 56 | printf("First wait\n");
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| 57 |
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| 58 | /* wait for the sqe to complete */
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| 59 | int ret = io_uring_wait_cqe(&ring, &cqe);
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| 60 |
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| 61 | /* read and process cqe event */
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| 62 | if(ret == 0) {
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| 63 | signed int len = cqe->res;
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| 64 | io_uring_cqe_seen(&ring, cqe);
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| 65 | printf("%d ", len);
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| 66 | if(len > 0) {
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| 67 | printf("%.*s", len, buf);
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| 68 | }
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| 69 | else if( len < 0 ) {
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| 70 | fprintf(stderr, "readv/read returned error : %s\n", strerror(-len));
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| 71 | }
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| 72 | }
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| 73 | else {
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| 74 | printf("%d\n", ret);
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| 75 | io_uring_cqe_seen(&ring, cqe);
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| 76 | }
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| 77 |
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| 78 | /* ============================================ */
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| 79 | /* DO it again so the we can compare behaviour. */
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| 80 | /* ============================================ */
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| 81 |
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| 82 | /* get an sqe and fill in a READ operation */
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| 83 | sqe = io_uring_get_sqe(&ring);
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| 84 | io_uring_prep_read(sqe, fd, buf, 8, 0);
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| 85 |
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| 86 | sqe->user_data = fd;
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| 87 |
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| 88 | printf("Second wait\n");
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| 89 |
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| 90 | /* tell the kernel we have an sqe ready for consumption */
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| 91 | io_uring_submit(&ring);
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| 92 |
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| 93 | /* wait for the sqe to complete */
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| 94 | ret = io_uring_wait_cqe(&ring, &cqe);
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| 95 |
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| 96 | /* read and process cqe event */
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| 97 | if(ret == 0) {
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| 98 | signed int len = cqe->res;
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| 99 | io_uring_cqe_seen(&ring, cqe);
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| 100 | printf("%d ", len);
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| 101 | if(len > 0) {
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| 102 | printf("%.*s", len, buf);
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| 103 | }
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| 104 | else if( len < 0 ) {
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| 105 | fprintf(stderr, "readv/read returned error : %s\n", strerror(-len));
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| 106 | }
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| 107 | }
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| 108 | else {
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| 109 | printf("%d\n", ret);
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| 110 | io_uring_cqe_seen(&ring, cqe);
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| 111 | }
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| 112 |
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| 113 | io_uring_queue_exit(&ring);
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| 114 |
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| 115 | close(fd);
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| 116 | }
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