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/* Emulation of copy_file_range.
Copyright (C) 2017 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/>. */
/* The following macros should be defined before including this
file:
COPY_FILE_RANGE_DECL Declaration specifiers for the function below.
COPY_FILE_RANGE Name of the function to define. */
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <limits.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
COPY_FILE_RANGE_DECL
ssize_t
COPY_FILE_RANGE (int infd, __off64_t *pinoff,
int outfd, __off64_t *poutoff,
size_t length, unsigned int flags)
{
if (flags != 0)
{
__set_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))
{
__set_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. */
__set_errno (EINVAL);
return -1;
}
if (instat.st_dev != outstat.st_dev)
{
/* Cross-device copies are not supported. */
__set_errno (EXDEV);
return -1;
}
}
/* The output descriptor must not have O_APPEND set. */
{
int flags = __fcntl (outfd, F_GETFL);
if (flags & O_APPEND)
{
__set_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 = __libc_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 = __libc_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) __libc_lseek64 (infd, -overread, SEEK_CUR);
__set_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;
}
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