76b61ebf1b
There's a failure case where an application gets a cqe entry, but
the kernel can then overwrite it before the application is done
reading it. This can happen since the io_uring_{get,wait}_completion()
interface both returns a CQE pointer AND increments the ring index.
If the kernel reuses this entry before the applications is done reading
it, the contents may be corrupted.
Remove the CQ head increment from the CQE retrieval, and put it into
a separate helper, io_uring_cqe_seen(). The application must call this
helper when it got a new CQE entry through one of the above calls, and
it's now done reading it.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
92 lines
1.8 KiB
C
92 lines
1.8 KiB
C
/*
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* Simple app that demonstrates how to setup an io_uring interface,
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* submit and complete IO against it, and then tear it down.
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*
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* gcc -Wall -O2 -D_GNU_SOURCE -o io_uring-test io_uring-test.c -luring
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*/
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#include <stdio.h>
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#include <fcntl.h>
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#include <string.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include "../src/liburing.h"
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#define QD 4
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int main(int argc, char *argv[])
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{
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struct io_uring ring;
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int i, fd, ret, pending, done;
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struct io_uring_sqe *sqe;
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struct io_uring_cqe *cqe;
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struct iovec *iovecs;
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off_t offset;
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void *buf;
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if (argc < 2) {
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printf("%s: file\n", argv[0]);
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return 1;
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}
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ret = io_uring_queue_init(QD, &ring, 0);
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if (ret < 0) {
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fprintf(stderr, "queue_init: %s\n", strerror(-ret));
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return 1;
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}
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fd = open(argv[1], O_RDONLY | O_DIRECT);
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if (fd < 0) {
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perror("open");
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return 1;
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}
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iovecs = calloc(QD, sizeof(struct iovec));
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for (i = 0; i < QD; i++) {
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if (posix_memalign(&buf, 4096, 4096))
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return 1;
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iovecs[i].iov_base = buf;
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iovecs[i].iov_len = 4096;
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}
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offset = 0;
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i = 0;
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do {
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sqe = io_uring_get_sqe(&ring);
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if (!sqe)
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break;
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io_uring_prep_readv(sqe, fd, &iovecs[i], 1, offset);
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offset += iovecs[i].iov_len;
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} while (1);
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ret = io_uring_submit(&ring);
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if (ret < 0) {
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fprintf(stderr, "io_uring_submit: %s\n", strerror(-ret));
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return 1;
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}
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done = 0;
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pending = ret;
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for (i = 0; i < pending; i++) {
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ret = io_uring_wait_completion(&ring, &cqe);
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if (ret < 0) {
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fprintf(stderr, "io_uring_get_completion: %s\n", strerror(-ret));
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return 1;
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}
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done++;
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ret = 0;
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if (cqe->res != 4096) {
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fprintf(stderr, "ret=%d, wanted 4096\n", cqe->res);
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ret = 1;
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}
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io_uring_cqe_seen(&ring, cqe);
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if (ret)
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break;
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}
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printf("Submitted=%d, completed=%d\n", pending, done);
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close(fd);
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io_uring_queue_exit(&ring);
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return 0;
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}
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