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Linux/kernel/trace/trace_seq.c

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

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