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