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(a)redhat.com&gt; --- fs/fuse/file.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 09ef2a4d25ed..ec20a1801c1b 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -2907,11 +2907,13 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset, }; int err; bool lock_inode = !(mode & FALLOC_FL_KEEP_SIZE) || - (mode & FALLOC_FL_PUNCH_HOLE); + (mode & (FALLOC_FL_PUNCH_HOLE | + FALLOC_FL_ZERO_RANGE)); bool block_faults = FUSE_IS_DAX(inode) && lock_inode; - if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)) + if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE | + FALLOC_FL_ZERO_RANGE)) return -EOPNOTSUPP; if (fm->fc->no_fallocate) @@ -2926,7 +2928,7 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset, goto out; } - if (mode & FALLOC_FL_PUNCH_HOLE) { + if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) { loff_t endbyte = offset + length - 1; err = fuse_writeback_range(inode, offset, endbyte); @@ -2966,7 +2968,7 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset, file_update_time(file); } - if (mode & FALLOC_FL_PUNCH_HOLE) + if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) truncate_pagecache_range(inode, offset, offset + length - 1); fuse_invalidate_attr(inode); -- 2.31.1