Index: head/lib/libc/sys/copy_file_range.2
===================================================================
--- head/lib/libc/sys/copy_file_range.2	(revision 354564)
+++ head/lib/libc/sys/copy_file_range.2	(revision 354565)
@@ -1,191 +1,192 @@
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 .\" Copyright (c) 2019 Rick Macklem
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 .\" $FreeBSD$
 .\"
-.Dd July 24, 2019
+.Dd November 8, 2019
 .Dt COPY_FILE_RANGE 2
 .Os
 .Sh NAME
 .Nm copy_file_range
 .Nd kernel copy of a byte range from one file to another
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
 .In sys/types.h
 .In unistd.h
 .Ft ssize_t
 .Fo copy_file_range
 .Fa "int infd"
 .Fa "off_t *inoffp"
 .Fa "int outfd"
 .Fa "off_t *outoffp"
 .Fa "size_t len"
 .Fa "unsigned int flags"
 .Fc
 .Sh DESCRIPTION
 The
 .Fn copy_file_range
 system call
 copies up to
 .Fa len
 bytes from
 .Fa infd
 to
 .Fa outfd
 in the kernel.
 It may do this using a file system specific technique if
 .Fa infd
 and
 .Fa outfd
 are on the same file system.
 The
 .Fa infd
 argument must be opened for reading and the
 .Fa outfd
 argument must be opened for writing, but not
 .Dv O_APPEND .
 If
 .Fa inoffp
 or
 .Fa outoffp
 is
 .Dv NULL ,
 the file offset for
 .Fa infd
 or
 .Fa outfd
 respectively will be used and updated by
 the number of bytes copied.
 If
 .Fa inoffp
 or
 .Fa outoffp
 is not
 .Dv NULL ,
 the byte offset pointed to by
 .Fa inoffp
 or
 .Fa outoffp
 respectively will be used/updated and the file offset for
 .Fa infd
 or
 .Fa outfd
 respectively will not be affected.
 The
 .Fa flags
 argument must be 0.
 .Pp
 This system call attempts to maintain holes in the output file for
 the byte range being copied.
 However, this does not always work well.
 It is recommended that sparse files be copied in a loop using
 .Xr lseek 2
 with
 .Dv SEEK_HOLE ,
 .Dv SEEK_DATA
 arguments and this system call for the
 data ranges found.
 .Pp
 .Sh RETURN VALUES
 If it succeeds, the call returns the number of bytes copied, which can be fewer
 than
 .Fa len .
+Returning fewer bytes than
+.Fa len
+does not necessarily indicate that EOF was reached.
+However, a return of zero for a non-zero
+.Fa len
+argument indicates that the offset for
+.Fa infd
+is at or beyond EOF.
 .Fn copy_file_range
 should be used in a loop until copying of the desired byte range has been
 completed.
 If an error has occurred, a \-1 is returned and the error code is placed in
 the global variable
 .Va errno .
 .Sh ERRORS
 The
 .Fn copy_file_range
 system call
 will fail if:
 .Bl -tag -width Er
 .It Bq Er EBADF
 If
 .Fa
 infd
 is not open for reading or
 .Fa
 outfd
 is not open for writing, or opened for writing with
 .Dv O_APPEND ,
 or if
 .Fa infd
 and
 .Fa outfd
 refer to the same file.
 .It Bq Er EFBIG
 If the copy exceeds the process's file size limit or the maximum file size
 for the file system
 .Fa outfd
 resides on.
 .It Bq Er EINTR
 A signal interrupted the system call
 before it could be completed.
 This may happen for files on some NFS mounts.
 When this happens, the values pointed to by
 .Fa inoffp
 and
 .Fa outoffp
 are reset to the initial values for the system call.
 .It Bq Er EINVAL
-If the initial offset for
-.Fa infd
-plus
-.Fa len
-exceeds EOF for
-.Fa infd
-or
 .Fa
 flags
 is not zero.
 .It Bq Er EIO
 An I/O error occurred while reading/writing the files.
 .It Bq Er EISDIR
 If either
 .Fa infd
 or
 .Fa outfd
 refers to a directory.
 .It Bq Er ENOSPC
 File system that stores
 .Fa outfd
 is full.
 .El
 .Sh SEE ALSO
 .Xr lseek 2
 .Sh STANDARDS
 The
 .Fn copy_file_range
 system call is expected to be compatible with the Linux system call of
 the same name.
 .Sh HISTORY
 The
 .Fn copy_file_range
 function appeared in
 .Fx 13.0 .