src/common/readwrite.cpp

   1 /*
   2  * Copyright (C) 2013 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   3  *
   4  * SPDX-License-Identifier: LGPL-2.1-only
   5  *
   6  */
   7
   8 #define _LGPL_SOURCE
   9 #include <limits.h>
  10 #include <unistd.h>
  11
  12 #include <common/compat/errno.hpp>
  13
  14 #include "readwrite.hpp"
  15
  16 /*
  17  * lttng_read and lttng_write take care of EINTR and partial read/write.
  18  * Upon success, they return the "count" received as parameter.
  19  * They can return a negative value if an error occurs.
  20  * If a value lower than the requested "count" is returned, it means an
  21  * error occurred.
  22  * The error can be checked by querying errno.
  23  */
  24 ssize_t lttng_read(int fd, void *buf, size_t count)
  25 {
  26         size_t i = 0;
  27         ssize_t ret;
  28
  29         LTTNG_ASSERT(buf);
  30
  31         /*
  32          * Deny a read count that can be bigger then the returned value max size.
  33          * This makes the function to never return an overflow value.
  34          */
  35         if (count > SSIZE_MAX) {
  36                 return -EINVAL;
  37         }
  38
  39         do {
  40                 ret = read(fd, (char *) buf + i, count - i);
  41                 if (ret < 0) {
  42                         if (errno == EINTR) {
  43                                 continue;       /* retry operation */
  44                         } else {
  45                                 goto error;
  46                         }
  47                 }
  48                 i += ret;
  49                 LTTNG_ASSERT(i <= count);
  50         } while (count - i > 0 && ret > 0);
  51         return i;
  52
  53 error:
  54         if (i == 0) {
  55                 return -1;
  56         } else {
  57                 return i;
  58         }
  59 }
  60
  61 ssize_t lttng_write(int fd, const void *buf, size_t count)
  62 {
  63         size_t i = 0;
  64         ssize_t ret;
  65
  66         LTTNG_ASSERT(buf);
  67
  68         /*
  69          * Deny a write count that can be bigger then the returned value max size.
  70          * This makes the function to never return an overflow value.
  71          */
  72         if (count > SSIZE_MAX) {
  73                 return -EINVAL;
  74         }
  75
  76         do {
  77                 ret = write(fd, (char *) buf + i, count - i);
  78                 if (ret < 0) {
  79                         if (errno == EINTR) {
  80                                 continue;       /* retry operation */
  81                         } else {
  82                                 goto error;
  83                         }
  84                 }
  85                 i += ret;
  86                 LTTNG_ASSERT(i <= count);
  87         } while (count - i > 0 && ret > 0);
  88         return i;
  89
  90 error:
  91         if (i == 0) {
  92                 return -1;
  93         } else {
  94                 return i;
  95         }
  96 }