[PATCH 2/3] fuse2fs: wrap the fuse_set_feature_flag helper for older libfuse

Darrick J. Wong
2025-05-22T00:07:56Z

Create a compatibility wrapper for fuse_set_feature_flag if the libfuse
version is older than the one where that function was introduced (3.17).

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
misc/fuse2fs.c | 32 +++++++++++++++++++++++++++++---
1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 9667f00e366a66..6137fc04198d39 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -932,6 +932,19 @@ static void op_destroy(void *p EXT2FS_ATTR((unused)))
}
}

+#if FUSE_VERSION < FUSE_MAKE_VERSION(3, 17)
+static inline int fuse_set_feature_flag(struct fuse_conn_info *conn,
+ uint64_t flag)
+{
+ if (conn->capable & flag) {
+ conn->want |= flag;
+ return 1;
+ }
+
+ return 0;
+}
+#endif
+
static void *op_init(struct fuse_conn_info *conn
#if FUSE_VERSION >= FUSE_MAKE_VERSION(3, 0)
, struct fuse_config *cfg EXT2FS_ATTR((unused))
@@ -947,14 +960,14 @@ static void *op_init(struct fuse_conn_info *conn
FUSE2FS_CHECK_CONTEXT_NULL(ff);
dbg_printf(ff, "%s: dev=%s\n", __func__, ff->device);
#ifdef FUSE_CAP_IOCTL_DIR
- conn->want |= FUSE_CAP_IOCTL_DIR;
+ fuse_set_feature_flag(conn, FUSE_CAP_IOCTL_DIR);
#endif
#ifdef FUSE_CAP_POSIX_ACL
if (ff->acl)
- conn->want |= FUSE_CAP_POSIX_ACL;
+ fuse_set_feature_flag(conn, FUSE_CAP_POSIX_ACL);
#endif
#ifdef FUSE_CAP_CACHE_SYMLINKS
- conn->want |= FUSE_CAP_CACHE_SYMLINKS;
+ fuse_set_feature_flag(conn, FUSE_CAP_CACHE_SYMLINKS);
#endif
#if FUSE_VERSION >= FUSE_MAKE_VERSION(3, 0)
conn->time_gran = 1;
@@ -1020,6 +1033,19 @@ static void *op_init(struct fuse_conn_info *conn
log_printf(ff, "%s %s.\n", _("mounted filesystem"), uuid);
}
out:
+#if FUSE_VERSION >= FUSE_MAKE_VERSION(3, 17)
+ /*
+ * THIS MUST GO LAST!
+ *
+ * The high-level libfuse code has a strange bug: it sets feature flags
+ * in conn->want_ext, and later copies the lower 32 bits to conn->want.
+ * If we in turn change some bits in want_ext without updating want,
+ * the lower level library to observe that both want and want_ext have
+ * gotten out of sync, and refuses to mount. Therefore, synchronize
+ * the two.
+ */
+ conn->want = conn->want_ext & 0xFFFFFFFF;
+#endif
return ff;
mount_fail:
ff->retcode = 32;