my_pread.cc

/* Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   Without limiting anything contained in the foregoing, this file,
   which is part of C Driver for MySQL (Connector/C), is also subject to the
   Universal FOSS Exception, version 1.0, a copy of which can be found at
   http://oss.oracle.com/licenses/universal-foss-exception.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/**
  @file mysys/my_pread.cc
*/

#include "my_config.h"

#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <stdio.h>
#include <sys/types.h>

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "my_base.h"
#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_io.h"
#include "my_sys.h"
#include "my_thread_local.h"
#include "mysys_err.h"
#if defined(_WIN32)
#include "mysys/mysys_priv.h"
#endif

#ifndef _WIN32
// Mock away pwrite() for unit testing.
ssize_t (*mock_pwrite)(int fd, const void *buf, size_t count,
                       off_t offset) = nullptr;
#endif

/*
  Read a chunk of bytes from a file from a given position

  SYNOPSIOS
    my_pread()
    Filedes	File decsriptor
    Buffer	Buffer to read data into
    Count	Number of bytes to read
    offset	Position to read from
    MyFlags	Flags

  NOTES
    This differs from the normal pread() call in that we don't care
    to set the position in the file back to the original position
    if the system doesn't support pread().

  RETURN
    (size_t) -1   Error
    #             Number of bytes read
*/

size_t my_pread(File Filedes, uchar *Buffer, size_t Count, my_off_t offset,
                myf MyFlags) {
  size_t readbytes;
  int error = 0;
  DBUG_ENTER("my_pread");
  DBUG_PRINT("my", ("fd: %d  Seek: %llu  Buffer: %p  Count: %lu  MyFlags: %d",
                    Filedes, (ulonglong)offset, Buffer, (ulong)Count, MyFlags));
  for (;;) {
    errno = 0; /* Linux, Windows don't reset this on EOF/success */
#if defined(_WIN32)
    readbytes = my_win_pread(Filedes, Buffer, Count, offset);
#else
    readbytes = pread(Filedes, Buffer, Count, offset);
#endif
    error = (readbytes != Count);
    if (error) {
      set_my_errno(errno ? errno : -1);
      if (errno == 0 ||
          (readbytes != (size_t)-1 && (MyFlags & (MY_NABP | MY_FNABP))))
        set_my_errno(HA_ERR_FILE_TOO_SHORT);

      DBUG_PRINT("warning", ("Read only %d bytes off %u from %d, errno: %d",
                             (int)readbytes, (uint)Count, Filedes, my_errno()));

      if ((readbytes == 0 || readbytes == (size_t)-1) && errno == EINTR) {
        DBUG_PRINT("debug", ("my_pread() was interrupted and returned %d",
                             (int)readbytes));
        continue; /* Interrupted */
      }

      if (MyFlags & (MY_WME | MY_FAE | MY_FNABP)) {
        char errbuf[MYSYS_STRERROR_SIZE];
        if (readbytes == (size_t)-1)
          my_error(EE_READ, MYF(0), my_filename(Filedes), my_errno(),
                   my_strerror(errbuf, sizeof(errbuf), my_errno()));
        else if (MyFlags & (MY_NABP | MY_FNABP))
          my_error(EE_EOFERR, MYF(0), my_filename(Filedes), my_errno(),
                   my_strerror(errbuf, sizeof(errbuf), my_errno()));
      }
      if (readbytes == (size_t)-1 || (MyFlags & (MY_FNABP | MY_NABP)))
        DBUG_RETURN(MY_FILE_ERROR); /* Return with error */
    }
    if (MyFlags & (MY_NABP | MY_FNABP))
      DBUG_RETURN(0);       /* Read went ok; Return 0 */
    DBUG_RETURN(readbytes); /* purecov: inspected */
  }
} /* my_pread */

/**
  Write a chunk of bytes to a file at a given position

  SYNOPSIOS
    my_pwrite()
    Filedes	File decsriptor
    Buffer	Buffer to write data from
    Count	Number of bytes to write
    offset	Position to write to
    MyFlags	Flags

  NOTES
    This differs from the normal pwrite() call in that we don't care
    to set the position in the file back to the original position
    if the system doesn't support pwrite()

  if (MyFlags & (MY_NABP | MY_FNABP))
  returns
    0  if Count == 0
    On succes, 0
    On failure, (size_t)-1 == MY_FILE_ERROR

  otherwise
  returns
    0  if Count == 0
    On success, the number of bytes written.
    On partial success (if less than Count bytes could be written),
       the actual number of bytes written.
    On failure, (size_t)-1 == MY_FILE_ERROR
*/

size_t my_pwrite(File Filedes, const uchar *Buffer, size_t Count,
                 my_off_t offset, myf MyFlags) {
  size_t writtenbytes;
  size_t sum_written = 0;
  uint errors = 0;
  const size_t initial_count = Count;

  DBUG_ENTER("my_pwrite");
  DBUG_PRINT("my", ("fd: %d  Seek: %llu  Buffer: %p  Count: %lu  MyFlags: %d",
                    Filedes, offset, Buffer, (ulong)Count, MyFlags));

  for (;;) {
    errno = 0;
#if defined(_WIN32)
    writtenbytes = my_win_pwrite(Filedes, Buffer, Count, offset);
#else
    if (mock_pwrite)
      writtenbytes = mock_pwrite(Filedes, Buffer, Count, offset);
    else
      writtenbytes = pwrite(Filedes, Buffer, Count, offset);
#endif
    if (writtenbytes == Count) {
      sum_written += writtenbytes;
      break;
    }
    set_my_errno(errno);
    if (writtenbytes != (size_t)-1) {
      sum_written += writtenbytes;
      Buffer += writtenbytes;
      Count -= writtenbytes;
      offset += writtenbytes;
    }
    DBUG_PRINT("error", ("Write only %u bytes", (uint)writtenbytes));

    if (is_killed_hook(NULL))
      MyFlags &= ~MY_WAIT_IF_FULL; /* End if aborted by user */

    if ((my_errno() == ENOSPC || my_errno() == EDQUOT) &&
        (MyFlags & MY_WAIT_IF_FULL)) {
      wait_for_free_space(my_filename(Filedes), errors);
      errors++;
      continue;
    }
    if (writtenbytes != 0 && writtenbytes != (size_t)-1)
      continue;
    else if (my_errno() == EINTR) {
      continue;                                /* Retry */
    } else if (writtenbytes == 0 && !errors++) /* Retry once */
    {
      /* We may come here if the file quota is exeeded */
      continue;
    }
    break; /* Return bytes written */
  }
  if (MyFlags & (MY_NABP | MY_FNABP)) {
    if (sum_written == initial_count)
      DBUG_RETURN(0); /* Want only errors, not bytes written */
    if (MyFlags & (MY_WME | MY_FAE | MY_FNABP)) {
      char errbuf[MYSYS_STRERROR_SIZE];
      my_error(EE_WRITE, MYF(0), my_filename(Filedes), my_errno(),
               my_strerror(errbuf, sizeof(errbuf), my_errno()));
    }
    DBUG_RETURN(MY_FILE_ERROR);
  }
  DBUG_EXECUTE_IF("check", my_seek(Filedes, -1, SEEK_SET, MYF(0)););

  if (sum_written == 0) DBUG_RETURN(MY_FILE_ERROR);

  DBUG_RETURN(sum_written);
} /* my_pwrite */