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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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COPY_FILE_RANGE(2) Linux Programmer's Manual COPY_FILE_RANGE(2)
copy_file_range - Copy a range of data from one file to another
#define _GNU_SOURCE
#include <unistd.h>
ssize_t copy_file_range(int fd_in, loff_t *off_in,
int fd_out, loff_t *off_out,
size_t len, unsigned int flags);
The copy_file_range() system call performs an in-kernel copy between
two file descriptors without the additional cost of transferring data
from the kernel to user space and then back into the kernel. It
copies up to len bytes of data from the source file descriptor fd_in
to the target file descriptor fd_out, overwriting any data that
exists within the requested range of the target file.
The following semantics apply for off_in, and similar statements
apply to off_out:
* If off_in is NULL, then bytes are read from fd_in starting from
the file offset, and the file offset is adjusted by the number of
bytes copied.
* If off_in is not NULL, then off_in must point to a buffer that
specifies the starting offset where bytes from fd_in will be read.
The file offset of fd_in is not changed, but off_in is adjusted
appropriately.
fd_in and fd_out can refer to the same file. If they refer to the
same file, then the source and target ranges are not allowed to
overlap.
The flags argument is provided to allow for future extensions and
currently must be set to 0.
Upon successful completion, copy_file_range() will return the number
of bytes copied between files. This could be less than the length
originally requested. If the file offset of fd_in is at or past the
end of file, no bytes are copied, and copy_file_range() returns zero.
On error, copy_file_range() returns -1 and errno is set to indicate
the error.
EBADF One or more file descriptors are not valid.
EBADF fd_in is not open for reading; or fd_out is not open for
writing.
EBADF The O_APPEND flag is set for the open file description (see
open(2)) referred to by the file descriptor fd_out.
EFBIG An attempt was made to write at a position past the maximum
file offset the kernel supports.
EFBIG An attempt was made to write a range that exceeds the allowed
maximum file size. The maximum file size differs between
filesystem implementations and can be different from the
maximum allowed file offset.
EFBIG An attempt was made to write beyond the process's file size
resource limit. This may also result in the process receiving
a SIGXFSZ signal.
EINVAL The flags argument is not 0.
EINVAL fd_in and fd_out refer to the same file and the source and
target ranges overlap.
EINVAL Either fd_in or fd_out is not a regular file.
EIO A low-level I/O error occurred while copying.
EISDIR Either fd_in or fd_out refers to a directory.
ENOMEM Out of memory.
ENOSPC There is not enough space on the target filesystem to complete
the copy.
EOVERFLOW
The requested source or destination range is too large to
represent in the specified data types.
EPERM fd_out refers to an immutable file.
ETXTBSY
Either fd_in or fd_out refers to an active swap file.
EXDEV The files referred to by fd_in and fd_out are not on the same
mounted filesystem (pre Linux 5.3).
The copy_file_range() system call first appeared in Linux 4.5, but
glibc 2.27 provides a user-space emulation when it is not available.
A major rework of the kernel implementation occurred in 5.3. Areas
of the API that weren't clearly defined were clarified and the API
bounds are much more strictly checked than on earlier kernels.
Applications should target the behaviour and requirements of 5.3
kernels.
First support for cross-filesystem copies was introduced in Linux
5.3. Older kernels will return -EXDEV when cross-filesystem copies
are attempted.
The copy_file_range() system call is a nonstandard Linux and GNU
extension.
If fd_in is a sparse file, then copy_file_range() may expand any
holes existing in the requested range. Users may benefit from
calling copy_file_range() in a loop, and using the lseek(2) SEEK_DATA
and SEEK_HOLE operations to find the locations of data segments.
copy_file_range() gives filesystems an opportunity to implement "copy
acceleration" techniques, such as the use of reflinks (i.e., two or
more inodes that share pointers to the same copy-on-write disk
blocks) or server-side-copy (in the case of NFS).
#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <unistd.h>
/* On versions of glibc before 2.27, we must invoke copy_file_range()
using syscall(2) */
static loff_t
copy_file_range(int fd_in, loff_t *off_in, int fd_out,
loff_t *off_out, size_t len, unsigned int flags)
{
return syscall(__NR_copy_file_range, fd_in, off_in, fd_out,
off_out, len, flags);
}
int
main(int argc, char **argv)
{
int fd_in, fd_out;
struct stat stat;
loff_t len, ret;
if (argc != 3) {
fprintf(stderr, "Usage: %s <source> <destination>\n", argv[0]);
exit(EXIT_FAILURE);
}
fd_in = open(argv[1], O_RDONLY);
if (fd_in == -1) {
perror("open (argv[1])");
exit(EXIT_FAILURE);
}
if (fstat(fd_in, &stat) == -1) {
perror("fstat");
exit(EXIT_FAILURE);
}
len = stat.st_size;
fd_out = open(argv[2], O_CREAT | O_WRONLY | O_TRUNC, 0644);
if (fd_out == -1) {
perror("open (argv[2])");
exit(EXIT_FAILURE);
}
do {
ret = copy_file_range(fd_in, NULL, fd_out, NULL, len, 0);
if (ret == -1) {
perror("copy_file_range");
exit(EXIT_FAILURE);
}
len -= ret;
} while (len > 0 && ret > 0);
close(fd_in);
close(fd_out);
exit(EXIT_SUCCESS);
}
lseek(2), sendfile(2), splice(2)
This page is part of release 5.07 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2020-06-09 COPY_FILE_RANGE(2)
Pages that refer to this page: sendfile(2), sendfile64(2), splice(2), syscalls(2), xfs_io(8)
Copyright and license for this manual page
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