probes/lttng-probe-user.c

   1 /*
   2  * lttng-probe-user.c
   3  *
   4  * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; only
   9  * version 2.1 of the License.
  10  *
  11  * This library is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with this library; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 #include <linux/uaccess.h>
  22 #include "lttng-probe-user.h"
  23
  24 /*
  25  * Calculate string length. Include final null terminating character if there is
  26  * one, or ends at first fault. Disabling page faults ensures that we can safely
  27  * call this from pretty much any context, including those where the caller
  28  * holds mmap_sem, or any lock which nests in mmap_sem.
  29  */
  30 long lttng_strlen_user_inatomic(const char *addr)
  31 {
  32         long count = 0;
  33         mm_segment_t old_fs = get_fs();
  34
  35         set_fs(KERNEL_DS);
  36         pagefault_disable();
  37         for (;;) {
  38                 char v;
  39                 unsigned long ret;
  40
  41                 if (unlikely(!access_ok(VERIFY_READ,
  42                                 (__force const char __user *) addr,
  43                                 sizeof(v))))
  44                         break;
  45                 ret = __copy_from_user_inatomic(&v,
  46                         (__force const char __user *)(addr),
  47                         sizeof(v));
  48                 if (unlikely(ret > 0))
  49                         break;
  50                 count++;
  51                 if (unlikely(!v))
  52                         break;
  53                 addr++;
  54         }
  55         pagefault_enable();
  56         set_fs(old_fs);
  57         return count;
  58 }
  59 EXPORT_SYMBOL_GPL(lttng_strlen_user_inatomic);