1  /* An interface to read and write that retries (if necessary) until complete.
       2  
       3     Copyright (C) 1993-1994, 1997-2006, 2009-2023 Free Software Foundation, Inc.
       4  
       5     This file is free software: you can redistribute it and/or modify
       6     it under the terms of the GNU Lesser General Public License as
       7     published by the Free Software Foundation; either version 2.1 of the
       8     License, or (at your option) any later version.
       9  
      10     This file is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      13     GNU Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public License
      16     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      17  
      18  #include <config.h>
      19  
      20  /* Specification.  */
      21  #ifdef FULL_READ
      22  # include "full-read.h"
      23  #else
      24  # include "full-write.h"
      25  #endif
      26  
      27  #include <errno.h>
      28  
      29  #ifdef FULL_READ
      30  # include "safe-read.h"
      31  # define safe_rw safe_read
      32  # define full_rw full_read
      33  # undef const
      34  # define const /* empty */
      35  #else
      36  # include "safe-write.h"
      37  # define safe_rw safe_write
      38  # define full_rw full_write
      39  #endif
      40  
      41  #ifdef FULL_READ
      42  /* Set errno to zero upon EOF.  */
      43  # define ZERO_BYTE_TRANSFER_ERRNO 0
      44  #else
      45  /* Some buggy drivers return 0 when one tries to write beyond
      46     a device's end.  (Example: Linux 1.2.13 on /dev/fd0.)
      47     Set errno to ENOSPC so they get a sensible diagnostic.  */
      48  # define ZERO_BYTE_TRANSFER_ERRNO ENOSPC
      49  #endif
      50  
      51  /* Write(read) COUNT bytes at BUF to(from) descriptor FD, retrying if
      52     interrupted or if a partial write(read) occurs.  Return the number
      53     of bytes transferred.
      54     When writing, set errno if fewer than COUNT bytes are written.
      55     When reading, if fewer than COUNT bytes are read, you must examine
      56     errno to distinguish failure from EOF (errno == 0).  */
      57  size_t
      58  full_rw (int fd, const void *buf, size_t count)
      59  {
      60    size_t total = 0;
      61    const char *ptr = (const char *) buf;
      62  
      63    while (count > 0)
      64      {
      65        size_t n_rw = safe_rw (fd, ptr, count);
      66        if (n_rw == (size_t) -1)
      67          break;
      68        if (n_rw == 0)
      69          {
      70            errno = ZERO_BYTE_TRANSFER_ERRNO;
      71            break;
      72          }
      73        total += n_rw;
      74        ptr += n_rw;
      75        count -= n_rw;
      76      }
      77  
      78    return total;
      79  }