sysdeps/posix/writev.c

   1 /* Copyright (C) 1991-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <stdlib.h>
  19 #include <unistd.h>
  20 #include <string.h>
  21 #include <limits.h>
  22 #include <scratch_buffer.h>
  23 #include <stdbool.h>
  24 #include <sys/param.h>
  25 #include <sys/uio.h>
  26 #include <errno.h>
  27
  28
  29 static void
  30 ifree (struct scratch_buffer *sbuf)
  31 {
  32    scratch_buffer_free (sbuf);
  33 }
  34
  35 /* Write data pointed by the buffers described by VECTOR, which
  36    is a vector of COUNT 'struct iovec's, to file descriptor FD.
  37    The data is written in the order specified.
  38    Operates just like 'write' (see <unistd.h>) except that the data
  39    are taken from VECTOR instead of a contiguous buffer.  */
  40 ssize_t
  41 __writev (int fd, const struct iovec *vector, int count)
  42 {
  43   /* Find the total number of bytes to be written.  */
  44   size_t bytes = 0;
  45   for (int i = 0; i < count; ++i)
  46     {
  47       /* Check for ssize_t overflow.  */
  48       if (SSIZE_MAX - bytes < vector[i].iov_len)
  49         {
  50           __set_errno (EINVAL);
  51           return -1;
  52         }
  53       bytes += vector[i].iov_len;
  54     }
  55
  56   /* Allocate a temporary buffer to hold the data.  Use a scratch_buffer
  57      since it's faster for small buffer sizes but can handle larger
  58      allocations as well.  */
  59
  60   struct scratch_buffer __attribute__ ((__cleanup__ (ifree))) buf;
  61   scratch_buffer_init (&buf);
  62   if (!scratch_buffer_set_array_size (&buf, 1, bytes))
  63     /* XXX I don't know whether it is acceptable to try writing
  64        the data in chunks.  Probably not so we just fail here.  */
  65     return -1;
  66   char *buffer = buf.data;
  67
  68   /* Copy the data into BUFFER.  */
  69   size_t to_copy = bytes;
  70   char *bp = buffer;
  71   for (int i = 0; i < count; ++i)
  72     {
  73       size_t copy = MIN (vector[i].iov_len, to_copy);
  74
  75       bp = __mempcpy ((void *) bp, (void *) vector[i].iov_base, copy);
  76
  77       to_copy -= copy;
  78       if (to_copy == 0)
  79         break;
  80     }
  81
  82   ssize_t bytes_written = __write (fd, buffer, bytes);
  83
  84   return bytes_written;
  85 }
  86 libc_hidden_def (__writev)
  87 #ifndef __writev
  88 weak_alias (__writev, writev)
  89 #endif