1 /* Copyright (c) 2013 Nicira, Inc.
3 * Licensed under the Apache License, Version 2.0 (the "License");
4 * you may not use this file except in compliance with the License.
5 * You may obtain a copy of the License at:
7 * http://www.apache.org/licenses/LICENSE-2.0
9 * Unless required by applicable law or agreed to in writing, software
10 * distributed under the License is distributed on an "AS IS" BASIS,
11 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 * See the License for the specific language governing permissions and
13 * limitations under the License.
16 #ifndef ASYNC_APPEND_H
17 #define ASYNC_APPEND_H 1
21 /* This module defines a simple, abstract interface to asynchronous file I/O.
22 * It is currently used only for logging. Thus, for now the interface only
23 * supports appending to a file. Multiple implementations are possible
24 * depending on the operating system's degree and form of support for
27 * The comments below document the requirements on any implementation.
32 * Only a single thread may use a given 'struct async_append' at one time.
35 /* Enables using asynchronous I/O. Some implementations may treat this as a
38 * Before this function is called, the POSIX aio implementation uses ordinary
39 * synchronous I/O because some POSIX aio libraries actually use threads
40 * internally, which has enough cost and robustness implications that it's
41 * better to use asynchronous I/O only when it has real expected benefits.
43 * Must be called while the process is still single-threaded. May forbid the
44 * process from subsequently forking. */
45 void async_append_enable(void);
47 /* Creates and returns a new asynchronous appender for file descriptor 'fd',
48 * which the caller must have opened in append mode (O_APPEND).
50 * This function must always succeed. If the system is for some reason unable
51 * to support asynchronous I/O on 'fd' then the library must fall back to
53 struct async_append *async_append_create(int fd);
55 /* Destroys 'ap', without closing its underlying file descriptor. */
56 void async_append_destroy(struct async_append *ap);
58 /* Appends the 'size' bytes of 'data' to 'ap', asynchronously if possible. */
59 void async_append_write(struct async_append *ap,
60 const void *data, size_t size);
62 /* Blocks until all data asynchronously written to 'ap' with
63 * async_append_write() has been committed to the point that it will be written
64 * to disk barring an operating system or hardware failure. */
65 void async_append_flush(struct async_append *ap);
67 #endif /* async-append.h */