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Linux/kernel/trace/trace_seq.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * trace_seq.c
  4  *
  5  * Copyright (C) 2008-2014 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
  6  *
  7  * The trace_seq is a handy tool that allows you to pass a descriptor around
  8  * to a buffer that other functions can write to. It is similar to the
  9  * seq_file functionality but has some differences.
 10  *
 11  * To use it, the trace_seq must be initialized with trace_seq_init().
 12  * This will set up the counters within the descriptor. You can call
 13  * trace_seq_init() more than once to reset the trace_seq to start
 14  * from scratch.
 15  * 
 16  * The buffer size is currently PAGE_SIZE, although it may become dynamic
 17  * in the future.
 18  *
 19  * A write to the buffer will either succed or fail. That is, unlike
 20  * sprintf() there will not be a partial write (well it may write into
 21  * the buffer but it wont update the pointers). This allows users to
 22  * try to write something into the trace_seq buffer and if it fails
 23  * they can flush it and try again.
 24  *
 25  */
 26 #include <linux/uaccess.h>
 27 #include <linux/seq_file.h>
 28 #include <linux/trace_seq.h>
 29 
 30 /* How much buffer is left on the trace_seq? */
 31 #define TRACE_SEQ_BUF_LEFT(s) seq_buf_buffer_left(&(s)->seq)
 32 
 33 /* How much buffer is written? */
 34 #define TRACE_SEQ_BUF_USED(s) seq_buf_used(&(s)->seq)
 35 
 36 /*
 37  * trace_seq should work with being initialized with 0s.
 38  */
 39 static inline void __trace_seq_init(struct trace_seq *s)
 40 {
 41         if (unlikely(!s->seq.size))
 42                 trace_seq_init(s);
 43 }
 44 
 45 /**
 46  * trace_print_seq - move the contents of trace_seq into a seq_file
 47  * @m: the seq_file descriptor that is the destination
 48  * @s: the trace_seq descriptor that is the source.
 49  *
 50  * Returns 0 on success and non zero on error. If it succeeds to
 51  * write to the seq_file it will reset the trace_seq, otherwise
 52  * it does not modify the trace_seq to let the caller try again.
 53  */
 54 int trace_print_seq(struct seq_file *m, struct trace_seq *s)
 55 {
 56         int ret;
 57 
 58         __trace_seq_init(s);
 59 
 60         ret = seq_buf_print_seq(m, &s->seq);
 61 
 62         /*
 63          * Only reset this buffer if we successfully wrote to the
 64          * seq_file buffer. This lets the caller try again or
 65          * do something else with the contents.
 66          */
 67         if (!ret)
 68                 trace_seq_init(s);
 69 
 70         return ret;
 71 }
 72 
 73 /**
 74  * trace_seq_printf - sequence printing of trace information
 75  * @s: trace sequence descriptor
 76  * @fmt: printf format string
 77  *
 78  * The tracer may use either sequence operations or its own
 79  * copy to user routines. To simplify formating of a trace
 80  * trace_seq_printf() is used to store strings into a special
 81  * buffer (@s). Then the output may be either used by
 82  * the sequencer or pulled into another buffer.
 83  */
 84 void trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
 85 {
 86         unsigned int save_len = s->seq.len;
 87         va_list ap;
 88 
 89         if (s->full)
 90                 return;
 91 
 92         __trace_seq_init(s);
 93 
 94         va_start(ap, fmt);
 95         seq_buf_vprintf(&s->seq, fmt, ap);
 96         va_end(ap);
 97 
 98         /* If we can't write it all, don't bother writing anything */
 99         if (unlikely(seq_buf_has_overflowed(&s->seq))) {
100                 s->seq.len = save_len;
101                 s->full = 1;
102         }
103 }
104 EXPORT_SYMBOL_GPL(trace_seq_printf);
105 
106 /**
107  * trace_seq_bitmask - write a bitmask array in its ASCII representation
108  * @s:          trace sequence descriptor
109  * @maskp:      points to an array of unsigned longs that represent a bitmask
110  * @nmaskbits:  The number of bits that are valid in @maskp
111  *
112  * Writes a ASCII representation of a bitmask string into @s.
113  */
114 void trace_seq_bitmask(struct trace_seq *s, const unsigned long *maskp,
115                       int nmaskbits)
116 {
117         unsigned int save_len = s->seq.len;
118 
119         if (s->full)
120                 return;
121 
122         __trace_seq_init(s);
123 
124         seq_buf_printf(&s->seq, "%*pb", nmaskbits, maskp);
125 
126         if (unlikely(seq_buf_has_overflowed(&s->seq))) {
127                 s->seq.len = save_len;
128                 s->full = 1;
129         }
130 }
131 EXPORT_SYMBOL_GPL(trace_seq_bitmask);
132 
133 /**
134  * trace_seq_vprintf - sequence printing of trace information
135  * @s: trace sequence descriptor
136  * @fmt: printf format string
137  *
138  * The tracer may use either sequence operations or its own
139  * copy to user routines. To simplify formating of a trace
140  * trace_seq_printf is used to store strings into a special
141  * buffer (@s). Then the output may be either used by
142  * the sequencer or pulled into another buffer.
143  */
144 void trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args)
145 {
146         unsigned int save_len = s->seq.len;
147 
148         if (s->full)
149                 return;
150 
151         __trace_seq_init(s);
152 
153         seq_buf_vprintf(&s->seq, fmt, args);
154 
155         /* If we can't write it all, don't bother writing anything */
156         if (unlikely(seq_buf_has_overflowed(&s->seq))) {
157                 s->seq.len = save_len;
158                 s->full = 1;
159         }
160 }
161 EXPORT_SYMBOL_GPL(trace_seq_vprintf);
162 
163 /**
164  * trace_seq_bprintf - Write the printf string from binary arguments
165  * @s: trace sequence descriptor
166  * @fmt: The format string for the @binary arguments
167  * @binary: The binary arguments for @fmt.
168  *
169  * When recording in a fast path, a printf may be recorded with just
170  * saving the format and the arguments as they were passed to the
171  * function, instead of wasting cycles converting the arguments into
172  * ASCII characters. Instead, the arguments are saved in a 32 bit
173  * word array that is defined by the format string constraints.
174  *
175  * This function will take the format and the binary array and finish
176  * the conversion into the ASCII string within the buffer.
177  */
178 void trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary)
179 {
180         unsigned int save_len = s->seq.len;
181 
182         if (s->full)
183                 return;
184 
185         __trace_seq_init(s);
186 
187         seq_buf_bprintf(&s->seq, fmt, binary);
188 
189         /* If we can't write it all, don't bother writing anything */
190         if (unlikely(seq_buf_has_overflowed(&s->seq))) {
191                 s->seq.len = save_len;
192                 s->full = 1;
193                 return;
194         }
195 }
196 EXPORT_SYMBOL_GPL(trace_seq_bprintf);
197 
198 /**
199  * trace_seq_puts - trace sequence printing of simple string
200  * @s: trace sequence descriptor
201  * @str: simple string to record
202  *
203  * The tracer may use either the sequence operations or its own
204  * copy to user routines. This function records a simple string
205  * into a special buffer (@s) for later retrieval by a sequencer
206  * or other mechanism.
207  */
208 void trace_seq_puts(struct trace_seq *s, const char *str)
209 {
210         unsigned int len = strlen(str);
211 
212         if (s->full)
213                 return;
214 
215         __trace_seq_init(s);
216 
217         if (len > TRACE_SEQ_BUF_LEFT(s)) {
218                 s->full = 1;
219                 return;
220         }
221 
222         seq_buf_putmem(&s->seq, str, len);
223 }
224 EXPORT_SYMBOL_GPL(trace_seq_puts);
225 
226 /**
227  * trace_seq_putc - trace sequence printing of simple character
228  * @s: trace sequence descriptor
229  * @c: simple character to record
230  *
231  * The tracer may use either the sequence operations or its own
232  * copy to user routines. This function records a simple charater
233  * into a special buffer (@s) for later retrieval by a sequencer
234  * or other mechanism.
235  */
236 void trace_seq_putc(struct trace_seq *s, unsigned char c)
237 {
238         if (s->full)
239                 return;
240 
241         __trace_seq_init(s);
242 
243         if (TRACE_SEQ_BUF_LEFT(s) < 1) {
244                 s->full = 1;
245                 return;
246         }
247 
248         seq_buf_putc(&s->seq, c);
249 }
250 EXPORT_SYMBOL_GPL(trace_seq_putc);
251 
252 /**
253  * trace_seq_putmem - write raw data into the trace_seq buffer
254  * @s: trace sequence descriptor
255  * @mem: The raw memory to copy into the buffer
256  * @len: The length of the raw memory to copy (in bytes)
257  *
258  * There may be cases where raw memory needs to be written into the
259  * buffer and a strcpy() would not work. Using this function allows
260  * for such cases.
261  */
262 void trace_seq_putmem(struct trace_seq *s, const void *mem, unsigned int len)
263 {
264         if (s->full)
265                 return;
266 
267         __trace_seq_init(s);
268 
269         if (len > TRACE_SEQ_BUF_LEFT(s)) {
270                 s->full = 1;
271                 return;
272         }
273 
274         seq_buf_putmem(&s->seq, mem, len);
275 }
276 EXPORT_SYMBOL_GPL(trace_seq_putmem);
277 
278 /**
279  * trace_seq_putmem_hex - write raw memory into the buffer in ASCII hex
280  * @s: trace sequence descriptor
281  * @mem: The raw memory to write its hex ASCII representation of
282  * @len: The length of the raw memory to copy (in bytes)
283  *
284  * This is similar to trace_seq_putmem() except instead of just copying the
285  * raw memory into the buffer it writes its ASCII representation of it
286  * in hex characters.
287  */
288 void trace_seq_putmem_hex(struct trace_seq *s, const void *mem,
289                          unsigned int len)
290 {
291         unsigned int save_len = s->seq.len;
292 
293         if (s->full)
294                 return;
295 
296         __trace_seq_init(s);
297 
298         /* Each byte is represented by two chars */
299         if (len * 2 > TRACE_SEQ_BUF_LEFT(s)) {
300                 s->full = 1;
301                 return;
302         }
303 
304         /* The added spaces can still cause an overflow */
305         seq_buf_putmem_hex(&s->seq, mem, len);
306 
307         if (unlikely(seq_buf_has_overflowed(&s->seq))) {
308                 s->seq.len = save_len;
309                 s->full = 1;
310                 return;
311         }
312 }
313 EXPORT_SYMBOL_GPL(trace_seq_putmem_hex);
314 
315 /**
316  * trace_seq_path - copy a path into the sequence buffer
317  * @s: trace sequence descriptor
318  * @path: path to write into the sequence buffer.
319  *
320  * Write a path name into the sequence buffer.
321  *
322  * Returns 1 if we successfully written all the contents to
323  *   the buffer.
324  * Returns 0 if we the length to write is bigger than the
325  *   reserved buffer space. In this case, nothing gets written.
326  */
327 int trace_seq_path(struct trace_seq *s, const struct path *path)
328 {
329         unsigned int save_len = s->seq.len;
330 
331         if (s->full)
332                 return 0;
333 
334         __trace_seq_init(s);
335 
336         if (TRACE_SEQ_BUF_LEFT(s) < 1) {
337                 s->full = 1;
338                 return 0;
339         }
340 
341         seq_buf_path(&s->seq, path, "\n");
342 
343         if (unlikely(seq_buf_has_overflowed(&s->seq))) {
344                 s->seq.len = save_len;
345                 s->full = 1;
346                 return 0;
347         }
348 
349         return 1;
350 }
351 EXPORT_SYMBOL_GPL(trace_seq_path);
352 
353 /**
354  * trace_seq_to_user - copy the squence buffer to user space
355  * @s: trace sequence descriptor
356  * @ubuf: The userspace memory location to copy to
357  * @cnt: The amount to copy
358  *
359  * Copies the sequence buffer into the userspace memory pointed to
360  * by @ubuf. It starts from the last read position (@s->readpos)
361  * and writes up to @cnt characters or till it reaches the end of
362  * the content in the buffer (@s->len), which ever comes first.
363  *
364  * On success, it returns a positive number of the number of bytes
365  * it copied.
366  *
367  * On failure it returns -EBUSY if all of the content in the
368  * sequence has been already read, which includes nothing in the
369  * sequenc (@s->len == @s->readpos).
370  *
371  * Returns -EFAULT if the copy to userspace fails.
372  */
373 int trace_seq_to_user(struct trace_seq *s, char __user *ubuf, int cnt)
374 {
375         __trace_seq_init(s);
376         return seq_buf_to_user(&s->seq, ubuf, cnt);
377 }
378 EXPORT_SYMBOL_GPL(trace_seq_to_user);
379 

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