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 <linux/module.h>
  23 #include "lttng-probe-user.h"
  24
  25 /*
  26  * Calculate string length. Include final null terminating character if there is
  27  * one, or ends at first fault. Disabling page faults ensures that we can safely
  28  * call this from pretty much any context, including those where the caller
  29  * holds mmap_sem, or any lock which nests in mmap_sem.
  30  */
  31 long lttng_strlen_user_inatomic(const char *addr)
  32 {
  33         long count = 0;
  34         mm_segment_t old_fs = get_fs();
  35
  36         set_fs(KERNEL_DS);
  37         pagefault_disable();
  38         for (;;) {
  39                 char v;
  40                 unsigned long ret;
  41
  42                 if (unlikely(!access_ok(VERIFY_READ,
  43                                 (__force const char __user *) addr,
  44                                 sizeof(v))))
  45                         break;
  46                 ret = __copy_from_user_inatomic(&v,
  47                         (__force const char __user *)(addr),
  48                         sizeof(v));
  49                 if (unlikely(ret > 0))
  50                         break;
  51                 count++;
  52                 if (unlikely(!v))
  53                         break;
  54                 addr++;
  55         }
  56         pagefault_enable();
  57         set_fs(old_fs);
  58         return count;
  59 }
  60 EXPORT_SYMBOL_GPL(lttng_strlen_user_inatomic);