[Libguestfs] [PATCH v3] 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, 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 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>
---
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