/* Simplified copy_file_range with cross-device copy.

   Copyright (C) 2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <errno.h>

#include <fcntl.h>

#include <inttypes.h>

#include <limits.h>

#include <sys/stat.h>

#include <sys/types.h>

#include <unistd.h>

#include <support/support.h>

ssize_t

support_copy_file_range (int infd, __off64_t *pinoff,

			 int outfd, __off64_t *poutoff,

			 size_t length, unsigned int flags)

{

  if (flags != 0)

    {

      errno = EINVAL;

      return -1;

    }

  struct stat64 instat;

  struct stat64 outstat;

  if (fstat64 (infd, &instat) != 0 || fstat64 (outfd, &outstat) != 0)

    return -1;

  if (S_ISDIR (instat.st_mode) || S_ISDIR (outstat.st_mode))

    {

      errno = EISDIR;

      return -1;

    }

  if (!S_ISREG (instat.st_mode) || !S_ISREG (outstat.st_mode))

    {

      /* We need a regular input file so that the we can seek

	 backwards in case of a write failure.  */

      errno = EINVAL;

      return -1;

    }

  /* The output descriptor must not have O_APPEND set.  */

  if (fcntl (outfd, F_GETFL) & O_APPEND)

    {

      errno = EBADF;

      return -1;

    }

  /* Avoid an overflow in the result.  */

  if (length > SSIZE_MAX)

    length = SSIZE_MAX;

  /* Main copying loop.  The buffer size is arbitrary and is a

     trade-off between stack size consumption, cache usage, and

     amortization of system call overhead.  */

  size_t copied = 0;

  char buf[8192];

  while (length > 0)

    {

      size_t to_read = length;

      if (to_read > sizeof (buf))

	to_read = sizeof (buf);

      /* Fill the buffer.  */

      ssize_t read_count;

      if (pinoff == NULL)

	read_count = read (infd, buf, to_read);

      else

	read_count = pread64 (infd, buf, to_read, *pinoff);

      if (read_count == 0)

	/* End of file reached prematurely.  */

	return copied;

      if (read_count < 0)

	{

	  if (copied > 0)

	    /* Report the number of bytes copied so far.  */

	    return copied;

	  return -1;

	}

      if (pinoff != NULL)

	*pinoff += read_count;

      /* Write the buffer part which was read to the destination.  */

      char *end = buf + read_count;

      for (char *p = buf; p < end; )

	{

	  ssize_t write_count;

	  if (poutoff == NULL)

	    write_count = write (outfd, p, end - p);

	  else

	    write_count = pwrite64 (outfd, p, end - p, *poutoff);

	  if (write_count < 0)

	    {

	      /* Adjust the input read position to match what we have

		 written, so that the caller can pick up after the

		 error.  */

	      size_t written = p - buf;

	      /* NB: This needs to be signed so that we can form the

		 negative value below.  */

	      ssize_t overread = read_count - written;

	      if (pinoff == NULL)

		{

		  if (overread > 0)

		    {

		      /* We are on an error recovery path, so we

			 cannot deal with failure here.  */

		      int save_errno = errno;

		      (void) lseek64 (infd, -overread, SEEK_CUR);

		      errno = save_errno;

		    }

		}

	      else /* pinoff != NULL */

		*pinoff -= overread;

	      if (copied + written > 0)

		/* Report the number of bytes copied so far.  */

		return copied + written;

	      return -1;

	    }

	  p += write_count;

	  if (poutoff != NULL)

	    *poutoff += write_count;

	} /* Write loop.  */

      copied += read_count;

      length -= read_count;

    }

  return copied;

}