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

Message ID 20181025215147.36248-3-olga.kornievskaia@gmail.com
State New
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  • [1/1] man-page: copy_file_range(2) allow for cross-device copies
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Commit Message

Olga Kornievskaia Oct. 25, 2018, 9:51 p.m.
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.
 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.
 .BR copy_file_range ()