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1.1 root 1:
2:
3: canon.h Header file canon.h
4:
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7:
8: Portable layout of binary data
9:
10: #include <canon.h>
11: #include <sys/types.h>
12:
13: The layout of binary data varies among machines. For example,
14: the byte order of a 16-bit word on the PDP-11 is low-byte.high-
15: byte, whereas on the Z8000 it is high-byte.low-byte.
16:
17: To ensure that file systems can be ported among machines with
18: differing byte orders, COHERENT uses a canonical layout of binary
19: data. (The word ``canonical'' in this context means, ``of or
20: conforming to a general rule''.) Data not in primary memory
21: (e.g., on disk or communications line) must conform to COHERENT's
22: canonical layout.
23:
24: To insulate programs from the details of the difference between
25: the `natural' and canonical layouts, the COHERENT system provides
26: a set of procedures to convert from one layout to another. They
27: are as follows:
28:
29:
30: ccaannsshhoorrtt()Convert a sshhoorrtt
31: ccaanniinntt() Convert an iinntt
32: ccaannlloonngg() Convert a lloonngg
33: ccaannvvaaddddrr()Convert vvaaddddrr_tt
34: ccaannssiizzee() Convert ffssiizzee_tt
35: ccaannddaaddddrr()Convert ddaaddddrr_tt
36: ccaannttiimmee() Convert ttiimmee_tt
37: ccaannddeevv() Convert ddeevv_tt
38: ccaanniinnoo() Convert iinnoo_tt
39:
40:
41: Each procedure takes an lvalue of the indicated type, converts it
42: in place, and returns nothing. The argument should not have
43: side-effects. Each procedure is its own inverse. Several proce-
44: dures are designed for elements of file systems.
45:
46: The file formats that contain canonical binary data and the com-
47: mands that deal with them are as follows:
48:
49:
50: _F_o_r_m_a_t _C_o_m_m_a_n_d_s
51:
52: ar.h ar, ld, ranlib
53: dir.h ls, tar
54: l.out.h as, cc, db, ld, nm, size, strip
55:
56:
57: Any program that manipulates binary data within files must per-
58: form canonical conversion immediately upon input and immediately
59: before output. The following fragment of the source code to the
60: command df should be instructive:
61:
62:
63:
64: COHERENT Lexicon Page 1
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67:
68:
69: canon.h Header file canon.h
70:
71:
72:
73:
74: #include <stdio.h>
75: #include <canon.h>
76: #include <filsys.h>
77: char superb[BSIZE];
78:
79:
80:
81: .
82: .
83: .
84:
85:
86:
87: df(fs)
88: char *fs;
89: {
90: register struct filsys *sbp = &superb;
91: FILE *fp;
92: daddr_t nfree;
93:
94:
95:
96: if ((fp = fopen(fs, "r")) == NULL) {
97: perror(fs);
98: return (1);
99: }
100:
101:
102:
103: fseek(fp, (long)BSIZE, 0);
104: if (fread(superb, sizeof superb, 1, fp) != 1) {
105: fprintf(stderr, "%s: read error\n", fs);
106: return (1);
107: }
108:
109:
110:
111: candaddr(sbp->s_tfree);
112: candaddr(sbp->s_fsize);
113: canshort(sbp->s_isize);
114: nfree = sbp->s_tfree;
115:
116:
117:
118: if (nfree > sbp->s_fsize-sbp->s_isize || nfree < 0) {
119: fprintf(stderr, "%s: bad free count\n", fs);
120: return (1);
121: }
122:
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129:
130: COHERENT Lexicon Page 2
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134:
135: canon.h Header file canon.h
136:
137:
138:
139: printf("%s: %ld\n", fs, nfree);
140: fclose(fp);
141: return (0);
142: }
143:
144:
145: ***** Files *****
146:
147: <canon.h>
148:
149: ***** See Also *****
150:
151: ar.h, byte ordering, candaddr(), candev(), canino(), canint(),
152: canlong(), canshort(), cansize(), cantime(), canvaddr(), dir.h,
153: l.out.h, header files
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196: COHERENT Lexicon Page 3
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