[PATCH v2] copy_file_range.2: Document glibc wrapper instead of kernel syscall

[Alejandro Colomar <alx.manpages@xxxxxxxxx>]

Glibc uses 'off64_t' instead of 'loff_t'.

......

Glibc prototype:

$ syscall='copy_file_range';
$ ret='ssize_t';
$ find glibc/ -type f -name '*.h' \
  |xargs pcregrep -Mn "(?s)^[\w\s]*${ret}\s*${syscall}\s*\(.*?;";
glibc/posix/unistd.h:1121:
ssize_t copy_file_range (int __infd, __off64_t *__pinoff,
			 int __outfd, __off64_t *__poutoff,
			 size_t __length, unsigned int __flags);

......

Testing example:

$ man ./man2/copy_file_range.2 \
  |sed -n '/^EXAMPLES/,/^SEE ALSO/p' \
  |head -n -1 \
  |tail -n +2 \
  >copy_file_range.c
$ gcc -Wall -Wextra -Werror -pedantic
copy_file_range.c -o copy_file_range
$ ./copy_file_range 
Usage: ./copy_file_range <source> <destination>
$ tee a >/dev/null
asdf
$ tee b >/dev/null
qwerty
zxcvbn
$ ./copy_file_range a b
$ cat a
asdf
$ cat b
asdf


Signed-off-by: Alejandro Colomar <alx.manpages@xxxxxxxxx>
---
 man2/copy_file_range.2 | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/man2/copy_file_range.2 b/man2/copy_file_range.2
index 1692aa44a..611a39b80 100644
--- a/man2/copy_file_range.2
+++ b/man2/copy_file_range.2
@@ -30,8 +30,8 @@ copy_file_range \- Copy a range of data from one file to another
 .B #define _GNU_SOURCE
 .B #include <unistd.h>
 .PP
-.BI "ssize_t copy_file_range(int " fd_in ", loff_t *" off_in ,
-.BI "                        int " fd_out ", loff_t *" off_out ,
+.BI "ssize_t copy_file_range(int " fd_in ", off64_t *" off_in ,
+.BI "                        int " fd_out ", off64_t *" off_out ,
 .BI "                        size_t " len ", unsigned int " flags );
 .fi
 .SH DESCRIPTION
@@ -233,26 +233,14 @@ or server-side-copy (in the case of NFS).
 #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;
+    off64_t len, ret;
 
     if (argc != 3) {
         fprintf(stderr, "Usage: %s <source> <destination>\en", argv[0]);
-- 
2.29.2