1RFIO_PRESEEK(3) Rfio Library Functions RFIO_PRESEEK(3)
2
6 rfio_preseek - prefetch chunks of data from a file
7
9 #include <sys/types.h>
10 #include "rfio_api.h"
11 int rfio_preseek (int s, const struct iovec *iov, int iovnb);
13 Under Linux, for large files:
15 #define _LARGEFILE64_SOURCE
16 #include <sys/types.h>
17 #include "rfio_api.h"
18 int rfio_preseek64 (int s, const struct iovec64 *iov, int iovnb);
20 For large files, under other systems:
22 #include <sys/types.h>
23 #include "rfio_api.h"
24 int rfio_preseek64 (int s, const struct iovec64 *iov, int iovnb);
26
28 rfio_preseek prefetches chunks of data at given offsets into an inter‐
29 nal buffer (on the client side), using the descriptor s generated by a
30 previous rfio_open. The actual offset values and the lengths are given
31 in the array of structures iov. The number of chunks is specified by
32 iovnb.
33 rfio_preseek64 does the prefetch for large files, using an array of
35 structures of type iovec64 rather than an array of iovec.
36 RFIO_READOPT must be set to RFIO_READBUF, which is the default. The
38 default internal buffer size is 128 kB, but the buffer size can be set
39 with an entry RFIO IOBUFSIZE in shift.conf. Then rfio_read gets the
40 data from that buffer.
41
43 /* tpreseek - write NBRECORDS_TOWRITE records and
44 read back NBRECORDS_TOREAD using the rfio_preseek function */
45 #include <fcntl.h>
47 #include <stdio.h>
48 #if defined(_WIN32)
49 #include <winsock2.h>
50 #endif
51 #include "rfio_api.h"
52 #define NBRECORDS_TOREAD 5
53 #define NBRECORDS_TOWRITE 10
54 main(argc, argv)
56 int argc;
57 char **argv;
58 {
59 char buf[65536];
60 int errflg = 0;
61 int fd;
62 int i;
63 struct iovec iov[NBRECORDS_TOREAD];
64 int iovnb = NBRECORDS_TOREAD;
65 int j;
66 static int lengths[NBRECORDS_TOWRITE] = {4096, 32768, 16384, 8192,
67 65536, 32768, 16384, 4096, 65536, 8192};
68 static int records_toread[NBRECORDS_TOREAD] = {2, 4, 5, 8, 9};
69 #if defined(_WIN32)
70 WSADATA wsadata;
71 #endif
72 if (argc != 2) {
74 fprintf (stderr, "usage: tpreseek pathname\n");
75 exit (1);
76 }
77 #if defined(_WIN32)
78 if (WSAStartup (MAKEWORD (2, 0), &wsadata)) {
79 fprintf (stderr, "WSAStartup unsuccessful\n");
80 exit (2);
81 }
82 #endif
83 while (! errflg) {
84 /* Write variable length records.
86 * Each record is filled with the record index
87 */
88 if ((fd = rfio_open (argv[1],
90 O_WRONLY|O_CREAT|O_TRUNC, 0644)) < 0) {
91 rfio_perror ("rfio_open");
92 errflg++;
93 break;
94 }
95 for (j = 0; j < NBRECORDS_TOWRITE; j++) {
96 for (i = 0; i < lengths[j]; i++)
97 buf[i] = j;
98 if (rfio_write (fd, buf, lengths[j]) < 0) {
99 rfio_perror ("rfio_write");
100 errflg++;
101 break;
102 }
103 }
104 (void)rfio_close (fd);
105 if (errflg) break;
106 /* Prefetch a few records: the actual offsets and lengths
108 * of the records is set in the array of iov structures
109 */
110 if ((fd = rfio_open (argv[1], O_RDONLY)) < 0) {
112 rfio_perror ("rfio_open");
113 errflg++;
114 break;
115 }
116 for (j = 0; j < NBRECORDS_TOREAD; j++) {
117 /* compute record offset */
118 iov[j].iov_base = 0;
119 for (i = 0; i < records_toread[j]; i++)
120 iov[j].iov_base = (char *) iov[j].iov_base +
121 lengths[i];
122 /* set length */
123 iov[j].iov_len = lengths[records_toread[j]];
124 }
125 if (rfio_preseek (fd, iov, iovnb) < 0) {
126 rfio_perror ("rfio_preseek");
127 errflg++;
128 break;
129 }
130 /* Read back the records and check their cpntents */
132 for (j = 0; j < NBRECORDS_TOREAD; j++) {
134 if (rfio_lseek (fd, (off_t) iov[j].iov_base,
135 SEEK_SET) < 0) {
136 rfio_perror ("rfio_lseek");
137 errflg++;
138 break;
139 }
140 if (rfio_read (fd, buf, iov[j].iov_len) < 0) {
141 rfio_perror ("rfio_read");
142 errflg++;
143 break;
144 }
145 for (i = 0; i < iov[j].iov_len; i++) {
146 if (buf[i] != records_toread[j]) {
147 fprintf (stderr,
148 "incorrect data read, record %d\n",
149 records_toread[j]);
150 errflg++;
151 break;
152 }
153 }
154 if (errflg) break;
155 }
156 (void) rfio_close (fd);
157 break;
158 }
159 if (rfio_unlink (argv[1]) < 0) {
160 rfio_perror ("rfio_unlink");
161 errflg++;
162 }
163 #if defined(_WIN32)
164 WSACleanup();
165 #endif
166 exit (errflg ? 1 : 0);
167 }
168
170 This routine returns 0 if the operation was successful or -1 if the
171 operation failed. In the latter case, serrno is set appropriately.
172
174 EBADF s is not a valid descriptor.
175 EINVAL RFIO_READOPT is not set to RFIO_READBUF.
177 SENOSHOST Host unknown.
179 SENOSSERV Service unknown.
181 SETIMEDOUT Timed out.
183 SEBADVERSION Version ID mismatch.
185 SECONNDROP Connection closed by remote end.
187 SECOMERR Communication error.
189 SENORCODE Host did not return error number.
191
193 rfio_lseek(3), rfio_open(3), rfio_read(3)
194
196 LCG Grid Deployment Team
197LCG $Date: 2005/03/31 13:13:03 $ RFIO_PRESEEK(3)