|
HTML rendering created 2023-06-24 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | NOTES | BUGS | EXAMPLES | SEE ALSO |
|
|
|
copy_file_range(2) System Calls Manual copy_file_range(2)
copy_file_range - Copy a range of data from one file to another
Standard C library (libc, -lc)
#define _GNU_SOURCE
#include <unistd.h>
ssize_t copy_file_range(int fd_in, off64_t *_Nullable off_in,
int fd_out, off64_t *_Nullable 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.
EOPNOTSUPP (since Linux 5.19)
The filesystem does not support this operation.
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 (before Linux 5.3)
The files referred to by fd_in and fd_out are not on the
same filesystem.
EXDEV (since Linux 5.19)
The files referred to by fd_in and fd_out are not on the
same filesystem, and the source and target filesystems are
not of the same type, or do not support cross-filesystem
copy.
A major rework of the kernel implementation occurred in Linux
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.
Since Linux 5.19, cross-filesystem copies can be achieved when
both filesystems are of the same type, and that filesystem
implements support for it. See BUGS for behavior prior to Linux
5.19.
Applications should target the behaviour and requirements of
Linux 5.19, that was also backported to earlier stable kernels.
Linux, GNU.
Linux 4.5, but glibc 2.27 provides a user-space emulation when it
is not available.
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).
In Linux 5.3 to Linux 5.18, cross-filesystem copies were
implemented by the kernel, if the operation was not supported by
individual filesystems. However, on some virtual filesystems,
the call failed to copy, while still reporting success.
#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
int fd_in, fd_out;
off64_t len, ret;
struct stat stat;
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)
Linux man-pages 6.04 2023-03-30 copy_file_range(2)
Pages that refer to this page: sendfile(2), splice(2), syscalls(2), off_t(3type), xfs_io(8)
|
HTML rendering created 2023-06-24 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|