splice.c revision 0aa417a9515f9dc17523c1870f6409370e94ca19 
1/*
2 * splice engine
3 *
4 * IO engine that transfers data by doing splices to/from pipes and
5 * the files.
6 *
7 */
8#include <stdio.h>
9#include <stdlib.h>
10#include <unistd.h>
11#include <errno.h>
12#include <assert.h>
13#include <sys/poll.h>
14#include <sys/mman.h>
15
16#include "../fio.h"
17
18#ifdef FIO_HAVE_SPLICE
19
20struct spliceio_data {
21	int pipe[2];
22	int vmsplice_to_user;
23	int vmsplice_to_user_map;
24};
25
26/*
27 * vmsplice didn't use to support splicing to user space, this is the old
28 * variant of getting that job done. Doesn't make a lot of sense, but it
29 * uses splices to move data from the source into a pipe.
30 */
31static int fio_splice_read_old(struct thread_data *td, struct io_u *io_u)
32{
33	struct spliceio_data *sd = td->io_ops->data;
34	struct fio_file *f = io_u->file;
35	int ret, ret2, buflen;
36	off_t offset;
37	void *p;
38
39	offset = io_u->offset;
40	buflen = io_u->xfer_buflen;
41	p = io_u->xfer_buf;
42	while (buflen) {
43		int this_len = buflen;
44
45		if (this_len > SPLICE_DEF_SIZE)
46			this_len = SPLICE_DEF_SIZE;
47
48		ret = splice(f->fd, &offset, sd->pipe[1], NULL, this_len, SPLICE_F_MORE);
49		if (ret < 0) {
50			if (errno == ENODATA || errno == EAGAIN)
51				continue;
52
53			return -errno;
54		}
55
56		buflen -= ret;
57
58		while (ret) {
59			ret2 = read(sd->pipe[0], p, ret);
60			if (ret2 < 0)
61				return -errno;
62
63			ret -= ret2;
64			p += ret2;
65		}
66	}
67
68	return io_u->xfer_buflen;
69}
70
71/*
72 * We can now vmsplice into userspace, so do the transfer by splicing into
73 * a pipe and vmsplicing that into userspace.
74 */
75static int fio_splice_read(struct thread_data *td, struct io_u *io_u)
76{
77	struct spliceio_data *sd = td->io_ops->data;
78	struct fio_file *f = io_u->file;
79	struct iovec iov;
80	int ret , buflen, mmap_len;
81	off_t offset;
82	void *p, *map;
83
84restart:
85	ret = 0;
86	offset = io_u->offset;
87	mmap_len = buflen = io_u->xfer_buflen;
88
89	if (sd->vmsplice_to_user_map) {
90		map = mmap(io_u->xfer_buf, buflen, PROT_READ, MAP_PRIVATE|OS_MAP_ANON, 0, 0);
91		if (map == MAP_FAILED) {
92			td_verror(td, errno, "mmap io_u");
93			return -1;
94		}
95
96		p = map;
97	} else {
98		map = NULL;
99		p = io_u->xfer_buf;
100	}
101
102	while (buflen) {
103		int this_len = buflen;
104		int flags = 0;
105
106		if (this_len > SPLICE_DEF_SIZE) {
107			this_len = SPLICE_DEF_SIZE;
108			flags = SPLICE_F_MORE;
109		}
110
111		ret = splice(f->fd, &offset, sd->pipe[1], NULL, this_len,flags);
112		if (ret < 0) {
113			if (errno == ENODATA || errno == EAGAIN)
114				continue;
115
116			td_verror(td, errno, "splice-from-fd");
117			break;
118		}
119
120		buflen -= ret;
121		iov.iov_base = p;
122		iov.iov_len = ret;
123		p += ret;
124
125		while (iov.iov_len) {
126			ret = vmsplice(sd->pipe[0], &iov, 1, SPLICE_F_MOVE);
127			if (ret < 0) {
128				if (errno == EFAULT && sd->vmsplice_to_user_map) {
129					sd->vmsplice_to_user_map = 0;
130					munmap(map, mmap_len);
131					goto restart;
132				}
133				if (errno == EBADF) {
134					ret = -EBADF;
135					break;
136				}
137				td_verror(td, errno, "vmsplice");
138				break;
139			} else if (!ret) {
140				td_verror(td, ENODATA, "vmsplice");
141				ret = -1;
142				break;
143			}
144
145			iov.iov_len -= ret;
146			iov.iov_base += ret;
147		}
148		if (ret < 0)
149			break;
150	}
151
152	if (sd->vmsplice_to_user_map && munmap(map, mmap_len) < 0) {
153		td_verror(td, errno, "munnap io_u");
154		return -1;
155	}
156	if (ret < 0)
157		return ret;
158
159	return io_u->xfer_buflen;
160}
161
162/*
163 * For splice writing, we can vmsplice our data buffer directly into a
164 * pipe and then splice that to a file.
165 */
166static int fio_splice_write(struct thread_data *td, struct io_u *io_u)
167{
168	struct spliceio_data *sd = td->io_ops->data;
169	struct iovec iov = {
170		.iov_base = io_u->xfer_buf,
171		.iov_len = io_u->xfer_buflen,
172	};
173	struct pollfd pfd = { .fd = sd->pipe[1], .events = POLLOUT, };
174	struct fio_file *f = io_u->file;
175	off_t off = io_u->offset;
176	int ret, ret2;
177
178	while (iov.iov_len) {
179		if (poll(&pfd, 1, -1) < 0)
180			return errno;
181
182		ret = vmsplice(sd->pipe[1], &iov, 1, SPLICE_F_NONBLOCK);
183		if (ret < 0)
184			return -errno;
185
186		iov.iov_len -= ret;
187		iov.iov_base += ret;
188
189		while (ret) {
190			ret2 = splice(sd->pipe[0], NULL, f->fd, &off, ret, 0);
191			if (ret2 < 0)
192				return -errno;
193
194			ret -= ret2;
195		}
196	}
197
198	return io_u->xfer_buflen;
199}
200
201static int fio_spliceio_queue(struct thread_data *td, struct io_u *io_u)
202{
203	struct spliceio_data *sd = td->io_ops->data;
204	int ret;
205
206	fio_ro_check(td, io_u);
207
208	if (io_u->ddir == DDIR_READ) {
209		if (sd->vmsplice_to_user) {
210			ret = fio_splice_read(td, io_u);
211			/*
212			 * This kernel doesn't support vmsplice to user
213			 * space. Reset the vmsplice_to_user flag, so that
214			 * we retry below and don't hit this path again.
215			 */
216			if (ret == -EBADF)
217				sd->vmsplice_to_user = 0;
218		}
219		if (!sd->vmsplice_to_user)
220			ret = fio_splice_read_old(td, io_u);
221	} else if (io_u->ddir == DDIR_WRITE)
222		ret = fio_splice_write(td, io_u);
223	else
224		ret = fsync(io_u->file->fd);
225
226	if (ret != (int) io_u->xfer_buflen) {
227		if (ret >= 0) {
228			io_u->resid = io_u->xfer_buflen - ret;
229			io_u->error = 0;
230			return FIO_Q_COMPLETED;
231		} else
232			io_u->error = errno;
233	}
234
235	if (io_u->error) {
236		td_verror(td, io_u->error, "xfer");
237		if (io_u->error == EINVAL)
238			log_err("fio: looks like splice doesn't work on this"
239					" file system\n");
240	}
241
242	return FIO_Q_COMPLETED;
243}
244
245static void fio_spliceio_cleanup(struct thread_data *td)
246{
247	struct spliceio_data *sd = td->io_ops->data;
248
249	if (sd) {
250		close(sd->pipe[0]);
251		close(sd->pipe[1]);
252		free(sd);
253	}
254}
255
256static int fio_spliceio_init(struct thread_data *td)
257{
258	struct spliceio_data *sd = malloc(sizeof(*sd));
259
260	if (pipe(sd->pipe) < 0) {
261		td_verror(td, errno, "pipe");
262		free(sd);
263		return 1;
264	}
265
266	/*
267	 * Assume this work, we'll reset this if it doesn't
268	 */
269	sd->vmsplice_to_user = 1;
270
271	/*
272	 * Works with "real" vmsplice to user, eg mapping pages directly.
273	 * Reset if we fail.
274	 */
275	sd->vmsplice_to_user_map = 1;
276
277	/*
278	 * And if vmsplice_to_user works, we definitely need aligned
279	 * buffers. Just set ->odirect to force that.
280	 */
281	if (td_read(td))
282		td->o.odirect = 1;
283
284	td->io_ops->data = sd;
285	return 0;
286}
287
288static struct ioengine_ops ioengine = {
289	.name		= "splice",
290	.version	= FIO_IOOPS_VERSION,
291	.init		= fio_spliceio_init,
292	.queue		= fio_spliceio_queue,
293	.cleanup	= fio_spliceio_cleanup,
294	.open_file	= generic_open_file,
295	.close_file	= generic_close_file,
296	.flags		= FIO_SYNCIO,
297};
298
299#else /* FIO_HAVE_SPLICE */
300
301/*
302 * When we have a proper configure system in place, we simply wont build
303 * and install this io engine. For now install a crippled version that
304 * just complains and fails to load.
305 */
306static int fio_spliceio_init(struct thread_data fio_unused *td)
307{
308	fprintf(stderr, "fio: splice not available\n");
309	return 1;
310}
311
312static struct ioengine_ops ioengine = {
313	.name		= "splice",
314	.version	= FIO_IOOPS_VERSION,
315	.init		= fio_spliceio_init,
316};
317
318#endif
319
320static void fio_init fio_spliceio_register(void)
321{
322	register_ioengine(&ioengine);
323}
324
325static void fio_exit fio_spliceio_unregister(void)
326{
327	unregister_ioengine(&ioengine);
328}
329