src/port/pwritev.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * pwritev.c
   4  *        Implementation of pwritev(2) for platforms that lack one.
   5  *
   6  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   7  *
   8  * IDENTIFICATION
   9  *        src/port/pwritev.c
  10  *
  11  * Note that this implementation changes the current file position, unlike
  12  * the POSIX-like function, so we use the name pg_pwritev().
  13  *
  14  *-------------------------------------------------------------------------
  15  */
  16
  17
  18 #include "postgres.h"
  19
  20 #ifdef WIN32
  21 #include <windows.h>
  22 #else
  23 #include <unistd.h>
  24 #endif
  25
  26 #include "port/pg_iovec.h"
  27
  28 ssize_t
  29 pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset)
  30 {
  31 #ifdef HAVE_WRITEV
  32         if (iovcnt == 1)
  33                 return pg_pwrite(fd, iov[0].iov_base, iov[0].iov_len, offset);
  34         if (lseek(fd, offset, SEEK_SET) < 0)
  35                 return -1;
  36         return writev(fd, iov, iovcnt);
  37 #else
  38         ssize_t         sum = 0;
  39         ssize_t         part;
  40
  41         for (int i = 0; i < iovcnt; ++i)
  42         {
  43                 part = pg_pwrite(fd, iov[i].iov_base, iov[i].iov_len, offset);
  44                 if (part < 0)
  45                 {
  46                         if (i == 0)
  47                                 return -1;
  48                         else
  49                                 return sum;
  50                 }
  51                 sum += part;
  52                 offset += part;
  53                 if (part < iov[i].iov_len)
  54                         return sum;
  55         }
  56         return sum;
  57 #endif
  58 }