Add link SQE support

Just a basic test case that does various forms of linked nops, and
a sample bare bones copy program using linked reads and writes.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

examples/Makefile

@@ -1,10 +1,10 @@
 CFLAGS ?= -g -O2 -Wall -D_GNU_SOURCE -L../src/
 
-all_targets += io_uring-test io_uring-cp
+all_targets += io_uring-test io_uring-cp link-cp
 
 all: $(all_targets)
 
-test_srcs := io_uring-test.c io_uring-cp.c
+test_srcs := io_uring-test.c io_uring-cp.c link-cp.c
 
 test_objs := $(patsubst %.c,%.ol,$(test_srcs))
 
@@ -12,6 +12,8 @@ io_uring-test: io_uring-test.c
 	$(CC) $(CFLAGS) -o $@ io_uring-test.c -luring
 io_uring-cp: io_uring-cp.c
 	$(CC) $(CFLAGS) -o $@ io_uring-cp.c -luring
+link-cp: link-cp.c
+	$(CC) $(CFLAGS) -o $@ link-cp.c -luring
 
 clean:
 	rm -f $(all_targets) $(test_objs)

examples/link-cp.c

@@ -0,0 +1,163 @@
+/*
+ * Very basic proof-of-concept for doing a copy with linked SQEs. Needs a
+ * bit of error handling and short read love.
+ */
+#include <stdio.h>
+#include <fcntl.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <assert.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/ioctl.h>
+#include "../src/liburing.h"
+
+#define QD	64
+#define BS	(32*1024)
+
+struct io_data {
+	struct iovec iov;
+};
+
+static int infd, outfd;
+
+static int setup_context(unsigned entries, struct io_uring *ring)
+{
+	int ret;
+
+	ret = io_uring_queue_init(entries, ring, 0);
+	if (ret < 0) {
+		fprintf(stderr, "queue_init: %s\n", strerror(-ret));
+		return -1;
+	}
+
+	return 0;
+}
+
+static int get_file_size(int fd, off_t *size)
+{
+	struct stat st;
+
+	if (fstat(fd, &st) < 0)
+		return -1;
+	if (S_ISREG(st.st_mode)) {
+		*size = st.st_size;
+		return 0;
+	} else if (S_ISBLK(st.st_mode)) {
+		unsigned long long bytes;
+
+		if (ioctl(fd, BLKGETSIZE64, &bytes) != 0)
+			return -1;
+
+		*size = bytes;
+		return 0;
+	}
+
+	return -1;
+}
+
+static int queue_rw_pair(struct io_uring *ring, off_t size, off_t offset)
+{
+	struct io_uring_sqe *sqe;
+	struct io_data *data;
+
+	data = malloc(size + sizeof(*data));
+	data->iov.iov_base = data + 1;
+	data->iov.iov_len = size;
+
+	sqe = io_uring_get_sqe(ring);
+	io_uring_prep_readv(sqe, infd, &data->iov, 1, offset);
+	sqe->flags |= IOSQE_IO_LINK;
+
+	sqe = io_uring_get_sqe(ring);
+	io_uring_prep_writev(sqe, outfd, &data->iov, 1, offset);
+	io_uring_sqe_set_data(sqe, data);
+	return 0;
+}
+
+static void handle_cqe(struct io_uring_cqe *cqe)
+{
+	struct io_data *data;
+
+	data = io_uring_cqe_get_data(cqe);
+	if (!data)
+		return;
+
+	free(data);
+}
+
+static int copy_file(struct io_uring *ring, off_t insize)
+{
+	struct io_uring_cqe *cqe;
+	size_t this_size;
+	off_t offset;
+	int inflight;
+
+	offset = 0;
+	inflight = 0;
+	while (insize) {
+		int has_inflight = inflight;
+
+		while (inflight < QD) {
+			this_size = BS;
+			if (this_size > insize)
+				this_size = insize;
+			queue_rw_pair(ring, this_size, offset);
+			offset += this_size;
+			insize -= this_size;
+			inflight += 2;
+		}
+
+		if (has_inflight != inflight)
+			io_uring_submit(ring);
+
+		while (inflight >= QD) {
+			int ret;
+
+			ret = io_uring_wait_cqe(ring, &cqe);
+			assert(ret >= 0);
+			handle_cqe(cqe);
+			inflight--;
+		}
+	}
+
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	struct io_uring ring;
+	off_t insize;
+	int ret;
+
+	if (argc < 3) {
+		printf("%s: infile outfile\n", argv[0]);
+		return 1;
+	}
+
+	infd = open(argv[1], O_RDONLY);
+	if (infd < 0) {
+		perror("open infile");
+		return 1;
+	}
+	outfd = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0644);
+	if (outfd < 0) {
+		perror("open outfile");
+		return 1;
+	}
+
+	if (setup_context(QD, &ring))
+		return 1;
+	if (get_file_size(infd, &insize))
+		return 1;
+
+	ret = copy_file(&ring, insize);
+
+	close(infd);
+	close(outfd);
+	io_uring_queue_exit(&ring);
+	return ret;
+}