kernel/trace/trace_printk.c

   1 /*
   2  * trace binary printk
   3  *
   4  * Copyright (C) 2008 Lai Jiangshan <laijs@cn.fujitsu.com>
   5  *
   6  */
   7 #include <linux/seq_file.h>
   8 #include <linux/uaccess.h>
   9 #include <linux/kernel.h>
  10 #include <linux/ftrace.h>
  11 #include <linux/string.h>
  12 #include <linux/module.h>
  13 #include <linux/mutex.h>
  14 #include <linux/ctype.h>
  15 #include <linux/list.h>
  16 #include <linux/slab.h>
  17
  18 #include "trace.h"
  19
  20 #ifdef CONFIG_MODULES
  21
  22 /*
  23  * modules trace_printk()'s formats are autosaved in struct trace_bprintk_fmt
  24  * which are queued on trace_bprintk_fmt_list.
  25  */
  26 static LIST_HEAD(trace_bprintk_fmt_list);
  27
  28 /* serialize accesses to trace_bprintk_fmt_list */
  29 static DEFINE_MUTEX(btrace_mutex);
  30
  31 struct trace_bprintk_fmt {
  32         struct list_head list;
  33         const char *fmt;
  34 };
  35
  36 static inline struct trace_bprintk_fmt *lookup_format(const char *fmt)
  37 {
  38         struct trace_bprintk_fmt *pos;
  39         list_for_each_entry(pos, &trace_bprintk_fmt_list, list) {
  40                 if (!strcmp(pos->fmt, fmt))
  41                         return pos;
  42         }
  43         return NULL;
  44 }
  45
  46 static
  47 void hold_module_trace_bprintk_format(const char **start, const char **end)
  48 {
  49         const char **iter;
  50         char *fmt;
  51
  52         /* allocate the trace_printk per cpu buffers */
  53         if (start != end)
  54                 trace_printk_init_buffers();
  55
  56         mutex_lock(&btrace_mutex);
  57         for (iter = start; iter < end; iter++) {
  58                 struct trace_bprintk_fmt *tb_fmt = lookup_format(*iter);
  59                 if (tb_fmt) {
  60                         *iter = tb_fmt->fmt;
  61                         continue;
  62                 }
  63
  64                 fmt = NULL;
  65                 tb_fmt = kmalloc(sizeof(*tb_fmt), GFP_KERNEL);
  66                 if (tb_fmt) {
  67                         fmt = kmalloc(strlen(*iter) + 1, GFP_KERNEL);
  68                         if (fmt) {
  69                                 list_add_tail(&tb_fmt->list, &trace_bprintk_fmt_list);
  70                                 strcpy(fmt, *iter);
  71                                 tb_fmt->fmt = fmt;
  72                         } else
  73                                 kfree(tb_fmt);
  74                 }
  75                 *iter = fmt;
  76
  77         }
  78         mutex_unlock(&btrace_mutex);
  79 }
  80
  81 static int module_trace_bprintk_format_notify(struct notifier_block *self,
  82                 unsigned long val, void *data)
  83 {
  84         struct module *mod = data;
  85         if (mod->num_trace_bprintk_fmt) {
  86                 const char **start = mod->trace_bprintk_fmt_start;
  87                 const char **end = start + mod->num_trace_bprintk_fmt;
  88
  89                 if (val == MODULE_STATE_COMING)
  90                         hold_module_trace_bprintk_format(start, end);
  91         }
  92         return 0;
  93 }
  94
  95 /*
  96  * The debugfs/tracing/printk_formats file maps the addresses with
  97  * the ASCII formats that are used in the bprintk events in the
  98  * buffer. For userspace tools to be able to decode the events from
  99  * the buffer, they need to be able to map the address with the format.
 100  *
 101  * The addresses of the bprintk formats are in their own section
 102  * __trace_printk_fmt. But for modules we copy them into a link list.
 103  * The code to print the formats and their addresses passes around the
 104  * address of the fmt string. If the fmt address passed into the seq
 105  * functions is within the kernel core __trace_printk_fmt section, then
 106  * it simply uses the next pointer in the list.
 107  *
 108  * When the fmt pointer is outside the kernel core __trace_printk_fmt
 109  * section, then we need to read the link list pointers. The trick is
 110  * we pass the address of the string to the seq function just like
 111  * we do for the kernel core formats. To get back the structure that
 112  * holds the format, we simply use containerof() and then go to the
 113  * next format in the list.
 114  */
 115 static const char **
 116 find_next_mod_format(int start_index, void *v, const char **fmt, loff_t *pos)
 117 {
 118         struct trace_bprintk_fmt *mod_fmt;
 119
 120         if (list_empty(&trace_bprintk_fmt_list))
 121                 return NULL;
 122
 123         /*
 124          * v will point to the address of the fmt record from t_next
 125          * v will be NULL from t_start.
 126          * If this is the first pointer or called from start
 127          * then we need to walk the list.
 128          */
 129         if (!v || start_index == *pos) {
 130                 struct trace_bprintk_fmt *p;
 131
 132                 /* search the module list */
 133                 list_for_each_entry(p, &trace_bprintk_fmt_list, list) {
 134                         if (start_index == *pos)
 135                                 return &p->fmt;
 136                         start_index++;
 137                 }
 138                 /* pos > index */
 139                 return NULL;
 140         }
 141
 142         /*
 143          * v points to the address of the fmt field in the mod list
 144          * structure that holds the module print format.
 145          */
 146         mod_fmt = container_of(v, typeof(*mod_fmt), fmt);
 147         if (mod_fmt->list.next == &trace_bprintk_fmt_list)
 148                 return NULL;
 149
 150         mod_fmt = container_of(mod_fmt->list.next, typeof(*mod_fmt), list);
 151
 152         return &mod_fmt->fmt;
 153 }
 154
 155 static void format_mod_start(void)
 156 {
 157         mutex_lock(&btrace_mutex);
 158 }
 159
 160 static void format_mod_stop(void)
 161 {
 162         mutex_unlock(&btrace_mutex);
 163 }
 164
 165 #else /* !CONFIG_MODULES */
 166 __init static int
 167 module_trace_bprintk_format_notify(struct notifier_block *self,
 168                 unsigned long val, void *data)
 169 {
 170         return 0;
 171 }
 172 static inline const char **
 173 find_next_mod_format(int start_index, void *v, const char **fmt, loff_t *pos)
 174 {
 175         return NULL;
 176 }
 177 static inline void format_mod_start(void) { }
 178 static inline void format_mod_stop(void) { }
 179 #endif /* CONFIG_MODULES */
 180
 181 static bool __read_mostly trace_printk_enabled = true;
 182
 183 void trace_printk_control(bool enabled)
 184 {
 185         trace_printk_enabled = enabled;
 186 }
 187
 188 __initdata_or_module static
 189 struct notifier_block module_trace_bprintk_format_nb = {
 190         .notifier_call = module_trace_bprintk_format_notify,
 191 };
 192
 193 int __trace_bprintk(unsigned long ip, const char *fmt, ...)
 194  {
 195         int ret;
 196         va_list ap;
 197
 198         if (unlikely(!fmt))
 199                 return 0;
 200
 201         if (!trace_printk_enabled)
 202                 return 0;
 203
 204         va_start(ap, fmt);
 205         ret = trace_vbprintk(ip, fmt, ap);
 206         va_end(ap);
 207         return ret;
 208 }
 209 EXPORT_SYMBOL_GPL(__trace_bprintk);
 210
 211 int __ftrace_vbprintk(unsigned long ip, const char *fmt, va_list ap)
 212  {
 213         if (unlikely(!fmt))
 214                 return 0;
 215
 216         if (!trace_printk_enabled)
 217                 return 0;
 218
 219         return trace_vbprintk(ip, fmt, ap);
 220 }
 221 EXPORT_SYMBOL_GPL(__ftrace_vbprintk);
 222
 223 int __trace_printk(unsigned long ip, const char *fmt, ...)
 224 {
 225         int ret;
 226         va_list ap;
 227
 228         if (!trace_printk_enabled)
 229                 return 0;
 230
 231         va_start(ap, fmt);
 232         ret = trace_vprintk(ip, fmt, ap);
 233         va_end(ap);
 234         return ret;
 235 }
 236 EXPORT_SYMBOL_GPL(__trace_printk);
 237
 238 int __ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap)
 239 {
 240         if (!trace_printk_enabled)
 241                 return 0;
 242
 243         return trace_vprintk(ip, fmt, ap);
 244 }
 245 EXPORT_SYMBOL_GPL(__ftrace_vprintk);
 246
 247 static const char **find_next(void *v, loff_t *pos)
 248 {
 249         const char **fmt = v;
 250         int start_index;
 251         int last_index;
 252
 253         start_index = __stop___trace_bprintk_fmt - __start___trace_bprintk_fmt;
 254
 255         if (*pos < start_index)
 256                 return __start___trace_bprintk_fmt + *pos;
 257
 258         /*
 259          * The __tracepoint_str section is treated the same as the
 260          * __trace_printk_fmt section. The difference is that the
 261          * __trace_printk_fmt section should only be used by trace_printk()
 262          * in a debugging environment, as if anything exists in that section
 263          * the trace_prink() helper buffers are allocated, which would just
 264          * waste space in a production environment.
 265          *
 266          * The __tracepoint_str sections on the other hand are used by
 267          * tracepoints which need to map pointers to their strings to
 268          * the ASCII text for userspace.
 269          */
 270         last_index = start_index;
 271         start_index = __stop___tracepoint_str - __start___tracepoint_str;
 272
 273         if (*pos < last_index + start_index)
 274                 return __start___tracepoint_str + (*pos - last_index);
 275
 276         start_index += last_index;
 277         return find_next_mod_format(start_index, v, fmt, pos);
 278 }
 279
 280 static void *
 281 t_start(struct seq_file *m, loff_t *pos)
 282 {
 283         format_mod_start();
 284         return find_next(NULL, pos);
 285 }
 286
 287 static void *t_next(struct seq_file *m, void * v, loff_t *pos)
 288 {
 289         (*pos)++;
 290         return find_next(v, pos);
 291 }
 292
 293 static int t_show(struct seq_file *m, void *v)
 294 {
 295         const char **fmt = v;
 296         const char *str = *fmt;
 297         int i;
 298
 299         if (!*fmt)
 300                 return 0;
 301
 302         seq_printf(m, "0x%lx : \"", *(unsigned long *)fmt);
 303
 304         /*
 305          * Tabs and new lines need to be converted.
 306          */
 307         for (i = 0; str[i]; i++) {
 308                 switch (str[i]) {
 309                 case '\n':
 310                         seq_puts(m, "\\n");
 311                         break;
 312                 case '\t':
 313                         seq_puts(m, "\\t");
 314                         break;
 315                 case '\\':
 316                         seq_putc(m, '\\');
 317                         break;
 318                 case '"':
 319                         seq_puts(m, "\\\"");
 320                         break;
 321                 default:
 322                         seq_putc(m, str[i]);
 323                 }
 324         }
 325         seq_puts(m, "\"\n");
 326
 327         return 0;
 328 }
 329
 330 static void t_stop(struct seq_file *m, void *p)
 331 {
 332         format_mod_stop();
 333 }
 334
 335 static const struct seq_operations show_format_seq_ops = {
 336         .start = t_start,
 337         .next = t_next,
 338         .show = t_show,
 339         .stop = t_stop,
 340 };
 341
 342 static int
 343 ftrace_formats_open(struct inode *inode, struct file *file)
 344 {
 345         return seq_open(file, &show_format_seq_ops);
 346 }
 347
 348 static const struct file_operations ftrace_formats_fops = {
 349         .open = ftrace_formats_open,
 350         .read = seq_read,
 351         .llseek = seq_lseek,
 352         .release = seq_release,
 353 };
 354
 355 static __init int init_trace_printk_function_export(void)
 356 {
 357         struct dentry *d_tracer;
 358
 359         d_tracer = tracing_init_dentry();
 360         if (IS_ERR(d_tracer))
 361                 return 0;
 362
 363         trace_create_file("printk_formats", 0444, d_tracer,
 364                                     NULL, &ftrace_formats_fops);
 365
 366         return 0;
 367 }
 368
 369 fs_initcall(init_trace_printk_function_export);
 370
 371 static __init int init_trace_printk(void)
 372 {
 373         return register_module_notifier(&module_trace_bprintk_format_nb);
 374 }
 375
 376 early_initcall(init_trace_printk);