1COPY_FILE_RANGE(2)         Linux Programmer's Manual        COPY_FILE_RANGE(2)
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NAME

6       copy_file_range - Copy a range of data from one file to another
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SYNOPSIS

9       #define _GNU_SOURCE
10       #include <unistd.h>
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12       ssize_t copy_file_range(int fd_in, off64_t *off_in,
13                               int fd_out, off64_t *off_out,
14                               size_t len, unsigned int flags);
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DESCRIPTION

17       The  copy_file_range()  system  call performs an in-kernel copy between
18       two file descriptors without the additional cost of  transferring  data
19       from the kernel to user space and then back into the kernel.  It copies
20       up to len bytes of data from the source file descriptor  fd_in  to  the
21       target  file descriptor fd_out, overwriting any data that exists within
22       the requested range of the target file.
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24       The following semantics apply for off_in, and similar statements  apply
25       to off_out:
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27       *  If  off_in is NULL, then bytes are read from fd_in starting from the
28          file offset, and the file offset is adjusted by the number of  bytes
29          copied.
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31       *  If off_in is not NULL, then off_in must point to a buffer that spec‐
32          ifies the starting offset where bytes from fd_in will be read.   The
33          file  offset  of fd_in is not changed, but off_in is adjusted appro‐
34          priately.
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36       fd_in and fd_out can refer to the same file.  If they refer to the same
37       file, then the source and target ranges are not allowed to overlap.
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39       The  flags argument is provided to allow for future extensions and cur‐
40       rently must be set to 0.
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RETURN VALUE

43       Upon successful completion, copy_file_range() will return the number of
44       bytes  copied between files.  This could be less than the length origi‐
45       nally requested.  If the file offset of fd_in is at or past the end  of
46       file, no bytes are copied, and copy_file_range() returns zero.
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48       On error, copy_file_range() returns -1 and errno is set to indicate the
49       error.
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ERRORS

52       EBADF  One or more file descriptors are not valid.
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54       EBADF  fd_in is not open for reading; or fd_out is not open  for  writ‐
55              ing.
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57       EBADF  The  O_APPEND  flag  is  set  for the open file description (see
58              open(2)) referred to by the file descriptor fd_out.
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60       EFBIG  An attempt was made to write at a position past the maximum file
61              offset the kernel supports.
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63       EFBIG  An  attempt  was  made to write a range that exceeds the allowed
64              maximum file  size.   The  maximum  file  size  differs  between
65              filesystem implementations and can be different from the maximum
66              allowed file offset.
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68       EFBIG  An attempt was made to write beyond the process's file size  re‐
69              source  limit.   This may also result in the process receiving a
70              SIGXFSZ signal.
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72       EINVAL The flags argument is not 0.
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74       EINVAL fd_in and fd_out refer to the same file and the source and  tar‐