1 /* buf.c - by Alen Stojanov and David van Moolenbroek, taken from procfs */
2
3 #include "devman.h"
4 #include "proto.h"
5 #include <stdarg.h>
6 #include <assert.h>
7
8 static char *buf;
9 static size_t left, used;
10 static off_t skip;
11
12 /*===========================================================================*
13 * buf_init *
14 *===========================================================================*/
buf_init(char * ptr,size_t len,off_t start)15 void buf_init(char *ptr, size_t len, off_t start)
16 {
17 /* Initialize the buffer for fresh use. The output is to be stored into
18 * 'ptr' which is BUF_SIZE bytes in size, since that is the size we
19 * requested. Due to the way vsnprintf works, we cannot use the last
20 * byte of this buffer. The first 'start' bytes of the produced output
21 * are to be skipped. After that, a total of 'len' bytes are requested.
22 */
23
24 buf = ptr;
25 skip = start;
26 left = MIN(len, BUF_SIZE - 1);
27 used = 0;
28 }
29
30 /*===========================================================================*
31 * buf_printf *
32 *===========================================================================*/
buf_printf(char * fmt,...)33 void buf_printf(char *fmt, ...)
34 {
35 /* Add formatted text to the end of the buffer.
36 */
37 va_list args;
38 ssize_t len, max;
39
40 if (left == 0)
41 return;
42
43 /* There is no way to estimate how much space the result will take, so
44 * we need to produce the string even when skipping part of the start.
45 * The null terminating character is not part of the result, so room
46 * must be given for it to be stored after completely filling up the
47 * requested part of the buffer.
48 */
49 max = MIN(skip + left + 1, BUF_SIZE);
50
51 va_start(args, fmt);
52 len = vsnprintf(&buf[used], max, fmt, args);
53 va_end(args);
54
55 /* The snprintf family returns the number of bytes that would be stored
56 * if the buffer were large enough, excluding the null terminator.
57 */
58 if (len >= BUF_SIZE)
59 len = BUF_SIZE - 1;
60
61 if (skip > 0) {
62 assert(used == 0);
63
64 if (skip >= len) {
65 skip -= len;
66
67 return;
68 }
69
70 memmove(buf, &buf[skip], len - skip);
71
72 len -= skip;
73 skip = 0;
74 }
75
76 assert(skip == 0);
77 assert(len >= 0);
78 assert((ssize_t) left >= 0);
79
80 if (len > (ssize_t) left)
81 len = left;
82
83 used += len;
84 left -= len;
85 }
86
87 /*===========================================================================*
88 * buf_append *
89 *===========================================================================*/
buf_append(char * data,size_t len)90 void buf_append(char *data, size_t len)
91 {
92 /* Add arbitrary data to the end of the buffer.
93 */
94
95 if (left == 0)
96 return;
97
98 if (skip > 0) {
99 if (skip >= (ssize_t) len) {
100 skip -= len;
101
102 return;
103 }
104
105 data += skip;
106 len -= skip;
107 skip = 0;
108 }
109
110 if (len > left)
111 len = left;
112
113 memcpy(&buf[used], data, len);
114
115 used += len;
116 left -= len;
117 }
118
119 /*===========================================================================*
120 * buf_result *
121 *===========================================================================*/
buf_result(void)122 ssize_t buf_result(void)
123 {
124 /* Return the resulting number of bytes produced, not counting the
125 * trailing null character in the buffer.
126 */
127
128 return used;
129 }
130