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6b1bdb56b1
The current fuse module filters out fallocate(FALLOC_FL_ZERO_RANGE) returning -EOPNOTSUPP. libnbd's nbdfuse would like to translate FALLOC_FL_ZERO_RANGE requests into the NBD command NBD_CMD_WRITE_ZEROES which allows NBD servers that support it to do zeroing efficiently. This commit treats this flag exactly like FALLOC_FL_PUNCH_HOLE. A way to test this, requiring fuse >= 3, nbdkit >= 1.8 and the latest nbdfuse from https://gitlab.com/nbdkit/libnbd/-/tree/master/fuse is to create a file containing some data and "mirror" it to a fuse file: $ dd if=/dev/urandom of=disk.img bs=1M count=1 $ nbdkit file disk.img $ touch mirror.img $ nbdfuse mirror.img nbd://localhost & (mirror.img -> nbdfuse -> NBD over loopback -> nbdkit -> disk.img) You can then run commands such as: $ fallocate -z -o 1024 -l 1024 mirror.img and check that the content of the original file ("disk.img") stays synchronized. To show NBD commands, export LIBNBD_DEBUG=1 before running nbdfuse. To clean up: $ fusermount3 -u mirror.img $ killall nbdkit Signed-off-by: Richard W.M. Jones <rjones@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>