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 <unistd.h>
  19 #include <errno.h>
  20 #include <assert.h>
  21 #include "readwrite.h"
  22
  23 /*
  24  * lttng_read and lttng_write take care of EINTR and partial read/write.
  25  * Upon success, they return the "count" received as parameter.
  26  * They can return a negative value if an error occurs.
  27  * If a value lower than the requested "count" is returned, it means an
  28  * error occured.
  29  * The error can be checked by querying errno.
  30  */
  31 ssize_t lttng_read(int fd, void *buf, size_t count)
  32 {
  33         size_t i = 0;
  34         ssize_t ret;
  35
  36         do {
  37                 ret = read(fd, buf + i, count - i);
  38                 if (ret < 0) {
  39                         if (errno == EINTR) {
  40                                 continue;       /* retry operation */
  41                         } else {
  42                                 goto error;
  43                         }
  44                 }
  45                 i += ret;
  46                 assert(i <= count);
  47         } while (count - i > 0 && ret > 0);
  48         return i;
  49
  50 error:
  51         if (i == 0) {
  52                 return -1;
  53         } else {
  54                 return i;
  55         }
  56 }
  57
  58 ssize_t lttng_write(int fd, const void *buf, size_t count)
  59 {
  60         size_t i = 0;
  61         ssize_t ret;
  62
  63         do {
  64                 ret = write(fd, buf + i, count - i);
  65                 if (ret < 0) {
  66                         if (errno == EINTR) {
  67                                 continue;       /* retry operation */
  68                         } else {
  69                                 goto error;
  70                         }
  71                 }
  72                 i += ret;
  73                 assert(i <= count);
  74         } while (count - i > 0 && ret > 0);
  75         return i;
  76
  77 error:
  78         if (i == 0) {
  79                 return -1;
  80         } else {
  81                 return i;
  82         }
  83 }