K 10
svn:author
V 8
rmacklem
K 8
svn:date
V 27
2019-08-15T23:21:41.294462Z
K 7
svn:log
V 796
Fix copy_file_range(2) so that unneeded blocks are not allocated to the output file.

When the byte range for copy_file_range(2) doesn't go to EOF on the
output file and there is a hole in the input file, a hole must be
"punched" in the output file. This is done by writing a block of bytes
all set to 0.
Without this patch, the write is done unconditionally which means that,
if the output file already has a hole in that byte range, a unneeded data block
of all 0 bytes would be allocated.
This patch adds code to check for a hole in the output file, so that it can
skip doing the write if there is already a hole in that byte range of
the output file. This avoids unnecessary allocation of blocks to the
output file.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D21155

END