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man:copy_file_range

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

NAME

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

SYNOPSIS

     #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);

DESCRIPTION

     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 file descriptor fd_in to  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 spec-

ifies 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 appro-
        priately.
     The flags argument is provided to allow for future extensions and  cur-
     rently must be to 0.

RETURN VALUE

     Upon successful completion, copy_file_range() will return the number of
     bytes copied between files.  This could be less than the length  origi-
     nally requested.
     On error, copy_file_range() returns -1 and errno is set to indicate the
     error.

ERRORS

     EBADF  One or more file descriptors are not valid; or fd_in is not open
            for  reading; or fd_out is not open for writing; or the O_APPEND
            flag is set for the open file description referred to by fd_out.
     EFBIG  An attempt was made to write a file that exceeds the implementa-
            tion-defined maximum file size or the process's file size limit,
            or to write at a position past the maximum allowed offset.
     EINVAL Requested  range  extends  beyond the end of the source file; or
            the flags argument is not 0.
     EIO    A low-level I/O error occurred while copying.
     EISDIR 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.
     EXDEV  The  files  referred  to  by file_in and file_out are not on the
            same mounted filesystem.

VERSIONS

     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.

CONFORMING TO

     The copy_file_range() system call is a nonstandard Linux and GNU exten-
     sion.

NOTES

     If file_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).

EXAMPLE

     #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);
         close(fd_in);
         close(fd_out);
         exit(EXIT_SUCCESS); }

SEE ALSO

     lseek(2), sendfile(2), splice(2)

COLOPHON

     This  page  is  part of release 4.16 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 2018-02-02 COPY_FILE_RANGE(2)

/data/webs/external/dokuwiki/data/pages/man/copy_file_range.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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