xref: /openbmc/linux/tools/lib/api/io.h (revision 82df5b73)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * Lightweight buffered reading library.
4  *
5  * Copyright 2019 Google LLC.
6  */
7 #ifndef __API_IO__
8 #define __API_IO__
9 
10 #include <stdlib.h>
11 #include <unistd.h>
12 
13 struct io {
14 	/* File descriptor being read/ */
15 	int fd;
16 	/* Size of the read buffer. */
17 	unsigned int buf_len;
18 	/* Pointer to storage for buffering read. */
19 	char *buf;
20 	/* End of the storage. */
21 	char *end;
22 	/* Currently accessed data pointer. */
23 	char *data;
24 	/* Set true on when the end of file on read error. */
25 	bool eof;
26 };
27 
28 static inline void io__init(struct io *io, int fd,
29 			    char *buf, unsigned int buf_len)
30 {
31 	io->fd = fd;
32 	io->buf_len = buf_len;
33 	io->buf = buf;
34 	io->end = buf;
35 	io->data = buf;
36 	io->eof = false;
37 }
38 
39 /* Reads one character from the "io" file with similar semantics to fgetc. */
40 static inline int io__get_char(struct io *io)
41 {
42 	char *ptr = io->data;
43 
44 	if (io->eof)
45 		return -1;
46 
47 	if (ptr == io->end) {
48 		ssize_t n = read(io->fd, io->buf, io->buf_len);
49 
50 		if (n <= 0) {
51 			io->eof = true;
52 			return -1;
53 		}
54 		ptr = &io->buf[0];
55 		io->end = &io->buf[n];
56 	}
57 	io->data = ptr + 1;
58 	return *ptr;
59 }
60 
61 /* Read a hexadecimal value with no 0x prefix into the out argument hex. If the
62  * first character isn't hexadecimal returns -2, io->eof returns -1, otherwise
63  * returns the character after the hexadecimal value which may be -1 for eof.
64  * If the read value is larger than a u64 the high-order bits will be dropped.
65  */
66 static inline int io__get_hex(struct io *io, __u64 *hex)
67 {
68 	bool first_read = true;
69 
70 	*hex = 0;
71 	while (true) {
72 		int ch = io__get_char(io);
73 
74 		if (ch < 0)
75 			return ch;
76 		if (ch >= '0' && ch <= '9')
77 			*hex = (*hex << 4) | (ch - '0');
78 		else if (ch >= 'a' && ch <= 'f')
79 			*hex = (*hex << 4) | (ch - 'a' + 10);
80 		else if (ch >= 'A' && ch <= 'F')
81 			*hex = (*hex << 4) | (ch - 'A' + 10);
82 		else if (first_read)
83 			return -2;
84 		else
85 			return ch;
86 		first_read = false;
87 	}
88 }
89 
90 /* Read a positive decimal value with out argument dec. If the first character
91  * isn't a decimal returns -2, io->eof returns -1, otherwise returns the
92  * character after the decimal value which may be -1 for eof. If the read value
93  * is larger than a u64 the high-order bits will be dropped.
94  */
95 static inline int io__get_dec(struct io *io, __u64 *dec)
96 {
97 	bool first_read = true;
98 
99 	*dec = 0;
100 	while (true) {
101 		int ch = io__get_char(io);
102 
103 		if (ch < 0)
104 			return ch;
105 		if (ch >= '0' && ch <= '9')
106 			*dec = (*dec * 10) + ch - '0';
107 		else if (first_read)
108 			return -2;
109 		else
110 			return ch;
111 		first_read = false;
112 	}
113 }
114 
115 #endif /* __API_IO__ */
116