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Rev Author # Line
1 perry 1 fdatasync - synchronize a file's in-core data with that on disk
2 !!SYNOPSIS
3
2 WikiAdmin 4 __#include <unistd.h>__
5 __#ifdef _POSIX_SYNCHRONIZED_IO__
6 __int fdatasync(int__ ''fd''__);__
7 __#endif__
1 perry 8
9 !!DESCRIPTION
2 WikiAdmin 10 fdatasync(2) flushes all data buffers of a file to disk (before the system call returns). It resembles fsync(2) but is not required to update the metadata such as access time.
1 perry 11
2 WikiAdmin 12 Applications that access databases or log files often write a tiny data fragment (e.g., one line in a log file) and then call fsync(2) immediately in order to ensure that the written data is physically stored on the harddisk. Unfortunately, fsync(2) will always initiate two write operations: one for the newly written data and another one in order to update the modification time stored in the inode. If the modification time is not a part of the transaction concept fdatasync(2) can be used to avoid unnecessary inode disk write operations.
1 perry 13
14 !!RETURN VALUE
2 WikiAdmin 15 On success, zero is returned. On error, -1 is returned, and ''errno'' is set appropriately.
1 perry 16
17 !!ERRORS
2 WikiAdmin 18 ;[EBADF]: ''fd'' is not a valid file descriptor open for writing.
19 ;[EROFS], [EINVAL]: ''fd'' is bound to a special file which does not support synchronization.
20 ;[EIO]: An error occurred during synchronization.
1 perry 21
2 WikiAdmin 22 !!BUGS
23 Currently (Linux 2.2) fdatasync(2) is equivalent to fsync(2)
1 perry 24
2 WikiAdmin 25 !!CONFORMING TO
26 POSIX1b (formerly POSIX.4)
1 perry 27
2 WikiAdmin 28 !!EXAMPLES
29 /*
30 * This program demonstrates fdatasync
31 *
32 */
1 perry 33
2 WikiAdmin 34 #include <sys/stat.h> /* for S_* constants */
35 #include <sys/types.h> /* for mode_t for creat() */
36 #include <string.h> /* for strerror() prototype */
37 #include <fcntl.h> /* for creat() prototype */
38 #include <stdio.h> /* for fprintf(),stderr protype */
39 #include <errno.h> /* for errno prototype */
40 #include <unistd.h> /* for write(2), fdatasync(2), close(2) prototypes */
1 perry 41
2 WikiAdmin 42 #define FILENAME "/tmp/fdatasync.example"
43 #define TEXT "blargh!\n"
1 perry 44
2 WikiAdmin 45 int main(int argc,char **argv)
46 {
47 int fd;
48 int err;
1 perry 49
2 WikiAdmin 50 fd = creat(FILENAME,S_IRUSR|S_IWUSR);
51 if (fd==-1) {
52 fprintf(
53 stderr,
54 "creat(\"%s\",S_IRUSR|S_IWUSR): %s (%i)\n",
55 FILENAME,
56 strerror(errno),
57 errno);
58 return 1;
59 }
1 perry 60
2 WikiAdmin 61 err=write(fd,TEXT,strlen(TEXT));
1 perry 62
2 WikiAdmin 63 if (err==-1) {
64 fprintf(
65 stderr,
66 "write(fd,\"%s\",strlen(\"%s\")): %s (%i)\n",
67 TEXT,
68 TEXT,
69 strerror(errno),
70 errno);
71 return 1;
72 }
1 perry 73
2 WikiAdmin 74 if (err!=strlen(TEXT)) {
75 fprintf(stderr,"Failed to write all the data, and I'm lazy and not "
76 "going to retry\n");
77 return 1;
78 }
1 perry 79
2 WikiAdmin 80 /* Flush the data only */
81 if (fdatasync(fd)==-1) {
82 fprintf(
83 stderr,
84 "fdatasync(fd): %s (%i)\n",
85 strerror(errno),
86 errno);
87 return 1;
88 }
1 perry 89
2 WikiAdmin 90 if (close(fd)==-1) {
91 fprintf(
92 stderr,
93 "close(fd): %s (%i)\n",
94 strerror(errno),
95 errno);
96 return 1;
97 }
1 perry 98
2 WikiAdmin 99 printf(
100 "%s successfully written\n",
101 FILENAME);
102 return 0;
103 }
1 perry 104
105
106 !!SEE ALSO
2 WikiAdmin 107 fsync(2), B.O. Gallmeister, POSIX.4, O'Reilly, pp. 220-223 and 343.
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