[PATCH 1/1] man-page: copy_file_range(2) allow for cross-device copies

[Olga Kornievskaia <olga.kornievskaia@gmail.com>]

From: Olga Kornievskaia <kolga@netapp.com>

A proposed VFS change removes the check for the files to reside
under the same file system. Instead, a file system driver implementation
is allowed to perform a cross-device copy_file_range() and if
the file system fails to support it instead fallback to doing
a do_splice copy. Therefore, EXDEV error code only applies to
kernel version prior to such support.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
---
 man2/copy_file_range.2 | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/man2/copy_file_range.2 b/man2/copy_file_range.2
index 20374ab..2cd9fae 100644
--- a/man2/copy_file_range.2
+++ b/man2/copy_file_range.2
@@ -39,7 +39,8 @@ The
 .BR 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.
+and then back into the kernel. Since kernel version 4.21(???) passed in
+file descriptors are not required to be under the same mounted file system.
 It copies up to
 .I len
 bytes of data from file descriptor
@@ -131,7 +132,8 @@ There is not enough space on the target filesystem to complete the copy.
 .B EXDEV
 The files referred to by
 .IR file_in " and " file_out
-are not on the same mounted filesystem.
+are not on the same mounted filesystem when the kernel does not support
+cross device file copy.
 .SH VERSIONS
 The
 .BR copy_file_range ()
-- 
1.8.3.1