1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 *
4 * Misc librarized functions for cmdline poking.
5 */
6 #include <linux/kernel.h>
7 #include <linux/string.h>
8 #include <linux/ctype.h>
9 #include <asm/setup.h>
10
11 static inline int myisspace(u8 c)
12 {
13 return c <= ' '; /* Close enough approximation */
14 }
15
16 /**
17 * Find a boolean option (like quiet,noapic,nosmp....)
18 *
19 * @cmdline: the cmdline string
20 * @option: option string to look for
21 *
22 * Returns the position of that @option (starts counting with 1)
23 * or 0 on not found. @option will only be found if it is found
24 * as an entire word in @cmdline. For instance, if @option="car"
25 * then a cmdline which contains "cart" will not match.
26 */
27 static int
28 __cmdline_find_option_bool(const char *cmdline, int max_cmdline_size,
29 const char *option)
30 {
31 char c;
32 int pos = 0, wstart = 0;
33 const char *opptr = NULL;
34 enum {
35 st_wordstart = 0, /* Start of word/after whitespace */
36 st_wordcmp, /* Comparing this word */
37 st_wordskip, /* Miscompare, skip */
38 } state = st_wordstart;
39
40 if (!cmdline)
41 return -1; /* No command line */
42
43 /*
44 * This 'pos' check ensures we do not overrun
45 * a non-NULL-terminated 'cmdline'
46 */
47 while (pos < max_cmdline_size) {
48 c = *(char *)cmdline++;
49 pos++;
50
51 switch (state) {
52 case st_wordstart:
53 if (!c)
54 return 0;
55 else if (myisspace(c))
56 break;
57
58 state = st_wordcmp;
59 opptr = option;
60 wstart = pos;
61 /* fall through */
62
63 case st_wordcmp:
64 if (!*opptr) {
65 /*
66 * We matched all the way to the end of the
67 * option we were looking for. If the
68 * command-line has a space _or_ ends, then
69 * we matched!
70 */
71 if (!c || myisspace(c))
72 return wstart;
73 /*
74 * We hit the end of the option, but _not_
75 * the end of a word on the cmdline. Not
76 * a match.
77 */
78 } else if (!c) {
79 /*
80 * Hit the NULL terminator on the end of
81 * cmdline.
82 */
83 return 0;
84 } else if (c == *opptr++) {
85 /*
86 * We are currently matching, so continue
87 * to the next character on the cmdline.
88 */
89 break;
90 }
91 state = st_wordskip;
92 /* fall through */
93
94 case st_wordskip:
95 if (!c)
96 return 0;
97 else if (myisspace(c))
98 state = st_wordstart;
99 break;
100 }
101 }
102
103 return 0; /* Buffer overrun */
104 }
105
106 /*
107 * Find a non-boolean option (i.e. option=argument). In accordance with
108 * standard Linux practice, if this option is repeated, this returns the
109 * last instance on the command line.
110 *
111 * @cmdline: the cmdline string
112 * @max_cmdline_size: the maximum size of cmdline
113 * @option: option string to look for
114 * @buffer: memory buffer to return the option argument
115 * @bufsize: size of the supplied memory buffer
116 *
117 * Returns the length of the argument (regardless of if it was
118 * truncated to fit in the buffer), or -1 on not found.
119 */
120 static int
121 __cmdline_find_option(const char *cmdline, int max_cmdline_size,
122 const char *option, char *buffer, int bufsize)
123 {
124 char c;
125 int pos = 0, len = -1;
126 const char *opptr = NULL;
127 char *bufptr = buffer;
128 enum {
129 st_wordstart = 0, /* Start of word/after whitespace */
130 st_wordcmp, /* Comparing this word */
131 st_wordskip, /* Miscompare, skip */
132 st_bufcpy, /* Copying this to buffer */
133 } state = st_wordstart;
134
135 if (!cmdline)
136 return -1; /* No command line */
137
138 /*
139 * This 'pos' check ensures we do not overrun
140 * a non-NULL-terminated 'cmdline'
141 */
142 while (pos++ < max_cmdline_size) {
143 c = *(char *)cmdline++;
144 if (!c)
145 break;
146
147 switch (state) {
148 case st_wordstart:
149 if (myisspace(c))
150 break;
151
152 state = st_wordcmp;
153 opptr = option;
154 /* fall through */
155
156 case st_wordcmp:
157 if ((c == '=') && !*opptr) {
158 /*
159 * We matched all the way to the end of the
160 * option we were looking for, prepare to
161 * copy the argument.
162 */
163 len = 0;
164 bufptr = buffer;
165 state = st_bufcpy;
166 break;
167 } else if (c == *opptr++) {
168 /*
169 * We are currently matching, so continue
170 * to the next character on the cmdline.
171 */
172 break;
173 }
174 state = st_wordskip;
175 /* fall through */
176
177 case st_wordskip:
178 if (myisspace(c))
179 state = st_wordstart;
180 break;
181
182 case st_bufcpy:
183 if (myisspace(c)) {
184 state = st_wordstart;
185 } else {
186 /*
187 * Increment len, but don't overrun the
188 * supplied buffer and leave room for the
189 * NULL terminator.
190 */
191 if (++len < bufsize)
192 *bufptr++ = c;
193 }
194 break;
195 }
196 }
197
198 if (bufsize)
199 *bufptr = '\0';
200
201 return len;
202 }
203
204 int cmdline_find_option_bool(const char *cmdline, const char *option)
205 {
206 return __cmdline_find_option_bool(cmdline, COMMAND_LINE_SIZE, option);
207 }
208
209 int cmdline_find_option(const char *cmdline, const char *option, char *buffer,
210 int bufsize)
211 {
212 return __cmdline_find_option(cmdline, COMMAND_LINE_SIZE, option,
213 buffer, bufsize);
214 }