linux-log_buf_read.patch

   1 Add two new functions for reading the kernel log buffer.  Their intention
   2 is to be used by recovery/dump/debug code so the kernel log can be easily
   3 retrieved/parsed in a crash scenario, but they are generic enough for other
   4 people to dream up other fun uses.
   5
   6 Signed-off-by: Mike Frysinger <vapier@gentoo.org>
   7 ---
   8 diff --git a/include/linux/kernel.h b/include/linux/kernel.h
   9 index 4300bb4..8d5b6c7 100644
  10 --- a/include/linux/kernel.h
  11 +++ b/include/linux/kernel.h
  12 @@ -156,6 +156,9 @@ asmlinkage int vprintk(const char *fmt, va_list args)
  13         __attribute__ ((format (printf, 1, 0)));
  14  asmlinkage int printk(const char * fmt, ...)
  15         __attribute__ ((format (printf, 1, 2))) __cold;
  16 +extern int log_buf_get_len(void);
  17 +extern int log_buf_read(int idx);
  18 +extern int log_buf_copy(char *dest, int idx, int len);
  19  #else
  20  static inline int vprintk(const char *s, va_list args)
  21         __attribute__ ((format (printf, 1, 0)));
  22 @@ -163,6 +166,9 @@ static inline int vprintk(const char *s, va_list args) { return 0; }
  23  static inline int printk(const char *s, ...)
  24         __attribute__ ((format (printf, 1, 2)));
  25  static inline int __cold printk(const char *s, ...) { return 0; }
  26 +static inline int log_buf_get_len(void) { return 0; }
  27 +static inline int log_buf_read(int idx); { return 0; }
  28 +static inline int log_buf_copy(char *dest, int idx, int len) { return 0; }
  29  #endif
  30
  31  unsigned long int_sqrt(unsigned long);
  32 diff --git a/kernel/printk.c b/kernel/printk.c
  33 index 051d27e..35b231a 100644
  34 --- a/kernel/printk.c
  35 +++ b/kernel/printk.c
  36 @@ -163,6 +163,55 @@ out:
  37  __setup("log_buf_len=", log_buf_len_setup);
  38
  39  /*
  40 + * Return the number of unread characters in the log buffer.
  41 + */
  42 +int log_buf_get_len(void)
  43 +{
  44 +       return log_end - log_start;
  45 +}
  46 +
  47 +/*
  48 + * Copy a range of characters from the log buffer.
  49 + */
  50 +int log_buf_copy(char *dest, int idx, int len)
  51 +{
  52 +       int ret, max;
  53 +
  54 +       if (!oops_in_progress)
  55 +               spin_lock_irq(&logbuf_lock);
  56 +
  57 +       max = log_buf_get_len();
  58 +       if (idx < 0 || idx >= max)
  59 +               ret = -1;
  60 +       else {
  61 +               if (len > max)
  62 +                       len = max;
  63 +               ret = len;
  64 +               while (len-- > 0) {
  65 +                       *dest = LOG_BUF(idx++);
  66 +                       ++dest;
  67 +               }
  68 +       }
  69 +
  70 +       if (!oops_in_progress)
  71 +               spin_unlock_irq(&logbuf_lock);
  72 +
  73 +       return ret;
  74 +}
  75 +
  76 +/*
  77 + * Extract a single character from the log buffer.
  78 + */
  79 +int log_buf_read(int idx)
  80 +{
  81 +       char ret;
  82 +       if (log_buf_copy(&ret, idx, 1) == 1)
  83 +               return ret;
  84 +       else
  85 +               return -1;
  86 +}
  87 +
  88 +/*
  89   * Commands to do_syslog:
  90   *
  91   *     0 -- Close the log.  Currently a NOP.