src/common/readwrite.c

   1 /*
   2  * Copyright (C) 2013 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   3  *
   4  * This library is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU Lesser General Public License, version 2.1 only,
   6  * as published by the Free Software Foundation.
   7  *
   8  * This library is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
  11  * for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public License
  14  * along with this library; if not, write to the Free Software Foundation,
  15  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  16  */
  17
  18 #include <assert.h>
  19 #include <errno.h>
  20 #include <limits.h>
  21 #include <unistd.h>
  22
  23 #include "readwrite.h"
  24
  25 /*
  26  * lttng_read and lttng_write take care of EINTR and partial read/write.
  27  * Upon success, they return the "count" received as parameter.
  28  * They can return a negative value if an error occurs.
  29  * If a value lower than the requested "count" is returned, it means an
  30  * error occured.
  31  * The error can be checked by querying errno.
  32  */
  33 ssize_t lttng_read(int fd, void *buf, size_t count)
  34 {
  35         size_t i = 0;
  36         ssize_t ret;
  37
  38         assert(buf);
  39
  40         /*
  41          * Deny a read count that can be bigger then the returned value max size.
  42          * This makes the function to never return an overflow value.
  43          */
  44         if (count > SSIZE_MAX) {
  45                 return -EINVAL;
  46         }
  47
  48         do {
  49                 ret = read(fd, buf + i, count - i);
  50                 if (ret < 0) {
  51                         if (errno == EINTR) {
  52                                 continue;       /* retry operation */
  53                         } else {
  54                                 goto error;
  55                         }
  56                 }
  57                 i += ret;
  58                 assert(i <= count);
  59         } while (count - i > 0 && ret > 0);
  60         return i;
  61
  62 error:
  63         if (i == 0) {
  64                 return -1;
  65         } else {
  66                 return i;
  67         }
  68 }
  69
  70 ssize_t lttng_write(int fd, const void *buf, size_t count)
  71 {
  72         size_t i = 0;
  73         ssize_t ret;
  74
  75         assert(buf);
  76
  77         /*
  78          * Deny a write count that can be bigger then the returned value max size.
  79          * This makes the function to never return an overflow value.
  80          */
  81         if (count > SSIZE_MAX) {
  82                 return -EINVAL;
  83         }
  84
  85         do {
  86                 ret = write(fd, buf + i, count - i);
  87                 if (ret < 0) {
  88                         if (errno == EINTR) {
  89                                 continue;       /* retry operation */
  90                         } else {
  91                                 goto error;
  92                         }
  93                 }
  94                 i += ret;
  95                 assert(i <= count);
  96         } while (count - i > 0 && ret > 0);
  97         return i;
  98
  99 error:
 100         if (i == 0) {
 101                 return -1;
 102         } else {
 103                 return i;
 104         }
 105 }