lib/sh/zread.c

   1 /* zread - read data from file descriptor into buffer with retries */
   2
   3 /* Copyright (C) 1999-2002 Free Software Foundation, Inc.
   4
   5    This file is part of GNU Bash, the Bourne Again SHell.
   6
   7    Bash is free software: you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation, either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    Bash is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with Bash.  If not, see <http://www.gnu.org/licenses/>.
  19 */
  20
  21 #include <config.h>
  22
  23 #include <sys/types.h>
  24
  25 #if defined (HAVE_UNISTD_H)
  26 #  include <unistd.h>
  27 #endif
  28
  29 #include <errno.h>
  30
  31 #if !defined (errno)
  32 extern int errno;
  33 #endif
  34
  35 #ifndef SEEK_CUR
  36 #  define SEEK_CUR 1
  37 #endif
  38
  39 /* Read LEN bytes from FD into BUF.  Retry the read on EINTR.  Any other
  40    error causes the loop to break. */
  41 ssize_t
  42 zread (fd, buf, len)
  43      int fd;
  44      char *buf;
  45      size_t len;
  46 {
  47   ssize_t r;
  48
  49   while ((r = read (fd, buf, len)) < 0 && errno == EINTR)
  50     ;
  51   return r;
  52 }
  53
  54 /* Read LEN bytes from FD into BUF.  Retry the read on EINTR, up to three
  55    interrupts.  Any other error causes the loop to break. */
  56
  57 #ifdef NUM_INTR
  58 #  undef NUM_INTR
  59 #endif
  60 #define NUM_INTR 3
  61
  62 ssize_t
  63 zreadintr (fd, buf, len)
  64      int fd;
  65      char *buf;
  66      size_t len;
  67 {
  68   ssize_t r;
  69   int nintr;
  70
  71   for (nintr = 0; ; )
  72     {
  73       r = read (fd, buf, len);
  74       if (r >= 0)
  75         return r;
  76       if (r == -1 && errno == EINTR)
  77         {
  78           if (++nintr > NUM_INTR)
  79             return -1;
  80           continue;
  81         }
  82       return r;
  83     }
  84 }
  85
  86 /* Read one character from FD and return it in CP.  Return values are as
  87    in read(2).  This does some local buffering to avoid many one-character
  88    calls to read(2), like those the `read' builtin performs. */
  89
  90 static char lbuf[128];
  91 static size_t lind, lused;
  92
  93 ssize_t
  94 zreadc (fd, cp)
  95      int fd;
  96      char *cp;
  97 {
  98   ssize_t nr;
  99
 100   if (lind == lused || lused == 0)
 101     {
 102       nr = zread (fd, lbuf, sizeof (lbuf));
 103       lind = 0;
 104       if (nr <= 0)
 105         {
 106           lused = 0;
 107           return nr;
 108         }
 109       lused = nr;
 110     }
 111   if (cp)
 112     *cp = lbuf[lind++];
 113   return 1;
 114 }
 115
 116 void
 117 zreset ()
 118 {
 119   lind = lused = 0;
 120 }
 121
 122 /* Sync the seek pointer for FD so that the kernel's idea of the last char
 123    read is the last char returned by zreadc. */
 124 void
 125 zsyncfd (fd)
 126      int fd;
 127 {
 128   off_t off;
 129   int r;
 130
 131   off = lused - lind;
 132   r = 0;
 133   if (off > 0)
 134     r = lseek (fd, -off, SEEK_CUR);
 135
 136   if (r >= 0)
 137     lused = lind = 0;
 138 }