From: Darrick J. Wong <djwong@xxxxxxxxxx>
XXX see the comment for why we have to do this bellicosely stupid thing.
Signed-off-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
---
misc/fuse2fs.c | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 82b59c1ac89774..e281b5fc589d82 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -261,6 +261,7 @@ struct fuse2fs {
uint8_t dirsync;
uint8_t unmount_in_destroy;
uint8_t noblkdev;
+ uint8_t can_hardlink;
enum fuse2fs_opstate opstate;
int blocklog;
@@ -1382,9 +1383,31 @@ static void *op_init(struct fuse_conn_info *conn
/*
* If we're mounting in iomap mode, we need to unmount in op_destroy
* so that the block device will be released before umount(2) returns.
+ *
+ * XXX: It turns out that fuse2fs creates internal node ids that have
+ * nothing to do with the ext2_ino_t that we give it. These internal
+ * node ids are what actually gets igetted in the kernel, which means
+ * that there can be multiple fuse_inode objects for the same fuse2fs
+ * inode.
+ *
+ * What this means, horrifyingly, is that on a fuse filesystem that
+ * supports hard links, the in-kernel i_rwsem does not protect against
+ * concurrent writes between files that point to the same inode. That
+ * in turn means that the file mode and size can get desynchronized
+ * between the multiple fuse_inode objects. This also means that we
+ * cannot cache iomaps in the kernel AT ALL because the caches will
+ * get out of sync, leading to WARN_ONs from the iomap zeroing code and
+ * probably data corruption after that.
+ *
+ * So for now we just disable hardlinking on iomap to see if the weird
+ * fstests failures (particularly g/476) go away. Long term it means
+ * we probably have to find a way around this, like porting fuse2fs
+ * to be a low level fuse driver.
*/
- if (fuse2fs_iomap_enabled(ff))
+ if (fuse2fs_iomap_enabled(ff)) {
ff->unmount_in_destroy = 1;
+ ff->can_hardlink = 0;
+ }
/* Clear the valid flag so that an unclean shutdown forces a fsck */
if (ff->opstate == F2OP_WRITABLE) {
@@ -2751,6 +2774,10 @@ static int op_link(const char *src, const char *dest)
int ret = 0;
FUSE2FS_CHECK_CONTEXT(ff);
+
+ if (!ff->can_hardlink)
+ return -ENOSYS;
+
dbg_printf(ff, "%s: src=%s dest=%s\n", __func__, src, dest);
temp_path = strdup(dest);
if (!temp_path) {
@@ -6380,6 +6407,7 @@ int main(int argc, char *argv[])
.iomap_state = IOMAP_UNKNOWN,
.iomap_dev = FUSE_IOMAP_DEV_NULL,
#endif
+ .can_hardlink = 1,
};
errcode_t err;
FILE *orig_stderr = stderr;
