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https://github.com/openvswitch/ovs
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68 lines
2.6 KiB
C
68 lines
2.6 KiB
C
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/* Copyright (c) 2013 Nicira, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef ASYNC_APPEND_H
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#define ASYNC_APPEND_H 1
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#include <stddef.h>
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/* This module defines a simple, abstract interface to asynchronous file I/O.
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* It is currently used only for logging. Thus, for now the interface only
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* supports appending to a file. Multiple implementations are possible
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* depending on the operating system's degree and form of support for
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* asynchronous I/O.
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*
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* The comments below document the requirements on any implementation.
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*
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* Thread-safety
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* =============
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*
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* Only a single thread may use a given 'struct async_append' at one time.
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*/
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/* Enables using asynchronous I/O. Some implementations may treat this as a
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* no-op.
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*
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* Before this function is called, the POSIX aio implementation uses ordinary
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* synchronous I/O because some POSIX aio libraries actually use threads
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* internally, which has enough cost and robustness implications that it's
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* better to use asynchronous I/O only when it has real expected benefits.
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*
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* Must be called while the process is still single-threaded. May forbid the
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* process from subsequently forking. */
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void async_append_enable(void);
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/* Creates and returns a new asynchronous appender for file descriptor 'fd',
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* which the caller must have opened in append mode (O_APPEND).
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*
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* This function must always succeed. If the system is for some reason unable
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* to support asynchronous I/O on 'fd' then the library must fall back to
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* syncrhonous I/O. */
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struct async_append *async_append_create(int fd);
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/* Destroys 'ap', without closing its underlying file descriptor. */
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void async_append_destroy(struct async_append *ap);
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/* Appends the 'size' bytes of 'data' to 'ap', asynchronously if possible. */
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void async_append_write(struct async_append *ap,
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const void *data, size_t size);
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/* Blocks until all data asynchronously written to 'ap' with
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* async_append_write() has been committed to the point that it will be written
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* to disk barring an operating system or hardware failure. */
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void async_append_flush(struct async_append *ap);
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#endif /* async-append.h */
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