2 * Copyright 2013 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef FOLLY_FILEUTIL_H_
18 #define FOLLY_FILEUTIL_H_
20 #include "folly/Portability.h"
28 * Convenience wrappers around some commonly used system calls. The *NoInt
29 * wrappers retry on EINTR. The *Full wrappers retry on EINTR and also loop
30 * until all data is written. Note that *Full wrappers weaken the thread
31 * semantics of underlying system calls.
33 int closeNoInt(int fd);
34 int fsyncNoInt(int fd);
35 int fdatasyncNoInt(int fd);
37 ssize_t readNoInt(int fd, void* buf, size_t n);
38 ssize_t preadNoInt(int fd, void* buf, size_t n, off_t offset);
39 ssize_t readvNoInt(int fd, const iovec* iov, int count);
41 ssize_t writeNoInt(int fd, const void* buf, size_t n);
42 ssize_t pwriteNoInt(int fd, const void* buf, size_t n, off_t offset);
43 ssize_t writevNoInt(int fd, const iovec* iov, int count);
46 * Wrapper around read() (and pread()) that, in addition to retrying on
47 * EINTR, will loop until all data is read.
49 * This wrapper is only useful for blocking file descriptors (for non-blocking
50 * file descriptors, you have to be prepared to deal with incomplete reads
51 * anyway), and only exists because POSIX allows read() to return an incomplete
52 * read if interrupted by a signal (instead of returning -1 and setting errno
55 * Note that this wrapper weakens the thread safety of read(): the file pointer
56 * is shared between threads, but the system call is atomic. If multiple
57 * threads are reading from a file at the same time, you don't know where your
58 * data came from in the file, but you do know that the returned bytes were
59 * contiguous. You can no longer make this assumption if using readFull().
60 * You should probably use pread() when reading from the same file descriptor
61 * from multiple threads simultaneously, anyway.
63 * Note that readvFull and preadvFull require iov to be non-const, unlike
64 * readv and preadv. The contents of iov after these functions return
67 ssize_t readFull(int fd, void* buf, size_t n);
68 ssize_t preadFull(int fd, void* buf, size_t n, off_t offset);
69 ssize_t readvFull(int fd, iovec* iov, int count);
70 #ifdef FOLLY_HAVE_PREADV
71 ssize_t preadvFull(int fd, iovec* iov, int count, off_t offset);
75 * Similar to readFull and preadFull above, wrappers around write() and
76 * pwrite() that loop until all data is written.
78 * Generally, the write() / pwrite() system call may always write fewer bytes
79 * than requested, just like read(). In certain cases (such as when writing to
80 * a pipe), POSIX provides stronger guarantees, but not in the general case.
81 * For example, Linux (even on a 64-bit platform) won't write more than 2GB in
82 * one write() system call.
84 * Note that writevFull and pwritevFull require iov to be non-const, unlike
85 * writev and pwritev. The contents of iov after these functions return
88 ssize_t writeFull(int fd, const void* buf, size_t n);
89 ssize_t pwriteFull(int fd, const void* buf, size_t n, off_t offset);
90 ssize_t writevFull(int fd, iovec* iov, int count);
91 #ifdef FOLLY_HAVE_PWRITEV
92 ssize_t pwritevFull(int fd, iovec* iov, int count, off_t offset);
97 #endif /* FOLLY_FILEUTIL_H_ */