157 lines
3.5 KiB
C
157 lines
3.5 KiB
C
#include <sys/types.h>
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#include <sys/stat.h>
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#include <sys/mman.h>
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#include <unistd.h>
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#include <errno.h>
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#include <string.h>
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#include "liburing.h"
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#include "barrier.h"
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static int __io_uring_get_cqe(struct io_uring *ring,
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struct io_uring_cqe **cqe_ptr, int wait)
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{
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struct io_uring_cq *cq = &ring->cq;
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const unsigned mask = *cq->kring_mask;
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unsigned head;
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int ret;
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*cqe_ptr = NULL;
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head = *cq->khead;
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do {
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/*
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* It's necessary to use a read_barrier() before reading
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* the CQ tail, since the kernel updates it locklessly. The
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* kernel has the matching store barrier for the update. The
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* kernel also ensures that previous stores to CQEs are ordered
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* with the tail update.
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*/
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read_barrier();
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if (head != *cq->ktail) {
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*cqe_ptr = &cq->cqes[head & mask];
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break;
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}
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if (!wait)
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break;
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ret = io_uring_enter(ring->ring_fd, 0, 1,
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IORING_ENTER_GETEVENTS, NULL);
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if (ret < 0)
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return -errno;
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} while (1);
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return 0;
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}
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/*
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* Return an IO completion, if one is readily available. Returns 0 with
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* cqe_ptr filled in on success, -errno on failure.
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*/
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int io_uring_peek_cqe(struct io_uring *ring, struct io_uring_cqe **cqe_ptr)
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{
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return __io_uring_get_cqe(ring, cqe_ptr, 0);
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}
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/*
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* Return an IO completion, waiting for it if necessary. Returns 0 with
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* cqe_ptr filled in on success, -errno on failure.
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*/
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int io_uring_wait_cqe(struct io_uring *ring, struct io_uring_cqe **cqe_ptr)
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{
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return __io_uring_get_cqe(ring, cqe_ptr, 1);
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}
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/*
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* Submit sqes acquired from io_uring_get_sqe() to the kernel.
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*
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* Returns number of sqes submitted
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*/
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int io_uring_submit(struct io_uring *ring)
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{
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struct io_uring_sq *sq = &ring->sq;
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const unsigned mask = *sq->kring_mask;
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unsigned ktail, ktail_next, submitted, to_submit;
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int ret;
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/*
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* If we have pending IO in the kring, submit it first. We need a
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* read barrier here to match the kernels store barrier when updating
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* the SQ head.
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*/
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read_barrier();
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if (*sq->khead != *sq->ktail) {
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submitted = *sq->kring_entries;
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goto submit;
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}
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if (sq->sqe_head == sq->sqe_tail)
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return 0;
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/*
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* Fill in sqes that we have queued up, adding them to the kernel ring
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*/
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submitted = 0;
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ktail = ktail_next = *sq->ktail;
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to_submit = sq->sqe_tail - sq->sqe_head;
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while (to_submit--) {
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ktail_next++;
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read_barrier();
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sq->array[ktail & mask] = sq->sqe_head & mask;
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ktail = ktail_next;
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sq->sqe_head++;
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submitted++;
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}
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if (!submitted)
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return 0;
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if (*sq->ktail != ktail) {
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/*
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* First write barrier ensures that the SQE stores are updated
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* with the tail update. This is needed so that the kernel
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* will never see a tail update without the preceeding sQE
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* stores being done.
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*/
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write_barrier();
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*sq->ktail = ktail;
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/*
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* The kernel has the matching read barrier for reading the
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* SQ tail.
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*/
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write_barrier();
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}
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submit:
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ret = io_uring_enter(ring->ring_fd, submitted, 0,
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IORING_ENTER_GETEVENTS, NULL);
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if (ret < 0)
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return -errno;
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return ret;
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}
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/*
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* Return an sqe to fill. Application must later call io_uring_submit()
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* when it's ready to tell the kernel about it. The caller may call this
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* function multiple times before calling io_uring_submit().
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*
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* Returns a vacant sqe, or NULL if we're full.
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*/
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struct io_uring_sqe *io_uring_get_sqe(struct io_uring *ring)
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{
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struct io_uring_sq *sq = &ring->sq;
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unsigned next = sq->sqe_tail + 1;
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struct io_uring_sqe *sqe;
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/*
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* All sqes are used
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*/
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if (next - sq->sqe_head > *sq->kring_entries)
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return NULL;
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sqe = &sq->sqes[sq->sqe_tail & *sq->kring_mask];
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sq->sqe_tail = next;
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return sqe;
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}
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