[Libguestfs] [PATCH v2] fuse: Allow fallocate(FALLOC_FL_ZERO_RANGE)
libnbd's nbdfuse utility would like to translate fallocate zero
requests into NBD_CMD_WRITE_ZEROES. Currently the fuse module filters
these out, returning -EOPNOTSUPP. This commit treats these almost the
same way as FALLOC_FL_PUNCH_HOLE except not calling
truncate_pagecache_range.
A way to test this is with the following script:
--------------------
#!/bin/bash
# Requires fuse >= 3, nbdkit >= 1.8, and latest nbdfuse from
# https://gitlab.com/nbdkit/libnbd/-/tree/master/fuse
set -e
set -x
export output=$PWD/output
rm -f test.img $output
# Create an nbdkit instance that prints the NBD requests seen.
nbdkit sh - <<'EOF'
case "$1" in
get_size) echo 1M ;;
can_write|can_trim|can_zero|can_fast_zero) ;;
pread) echo "$@" >>$output; dd if=/dev/zero count=$3 iflag=count_bytes
;;
pwrite) echo "$@" >>$output; cat >/dev/null ;;
trim|zero) echo "$@" >>$output ;;
*) exit 2 ;;
esac
EOF
# Fuse-mount NBD instance as a file.
touch test.img
nbdfuse test.img nbd://localhost & sleep 2
ls -lh test.img
# Run a read, write, trim and zero request.
dd if=test.img of=/dev/null bs=512 skip=1024 count=1
dd if=/dev/zero of=test.img bs=512 skip=2048 count=1
fallocate -p -l 512 -o 4096 test.img
fallocate -z -l 512 -o 8192 test.img
# Print the output from the NBD server.
cat $output
# Clean up.
fusermount3 -u test.img
killall nbdkit
rm test.img $output
--------------------
which will print:
pread 4096 524288 # number depends on readahead
pwrite 512 0
trim 512 4096
zero 512 8192 may_trim
The last line indicates that the FALLOC_FL_ZERO_RANGE request was
successfully passed through by the kernel module to nbdfuse,
translated to NBD_CMD_WRITE_ZEROES and sent through to the server.
Signed-off-by: Richard W.M. Jones <rjones(a)redhat.com>
---
fs/fuse/file.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 09ef2a4d25ed..22e8e88c78d4 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) ||
+ (mode & 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 +2928,8 @@ 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) ||
+ (mode & FALLOC_FL_ZERO_RANGE)) {
loff_t endbyte = offset + length - 1;
err = fuse_writeback_range(inode, offset, endbyte);
--
2.31.1