fuse: Fix want flag conversion

32-bit conn->want flags been left to be ABI compatible to 3.10,
even though the so version was changed.
The more recent way is to use fuse_set_feature_flag(),
which will use conn->want_ext.

Given that we now have two flags (want and want_ext), we need
to convert and that brought several issues
- If the application sets conn->want, that needs to be set into
  the lower 32 bit of  conn->want_ext. As the application might
  actually unset values, it really has to be a copy and not
  just 'or' - fixed now.
- convert_to_conn_want_ext() actually needs to check for
  _modified_ conn->want and conn->want_ext
- convert_to_conn_want_ext() must consider being called from
  high and lowlevel interfact, with different want_ext_default
  and want_default values. It is only a failure, if the application
  changed both, conn->want and conn->want_ext. This function
  was failing in issue #1171, because high level fuse_fs_init()
  was changing values and then lowlevel do_init() was incorrectly
  failing on that.

This also adds a new test (test_want_conversion) and sets
values into example/{hello.c,hello_ll.c}

Also some more internal users of conn->want are converted to
fuse_{set,unset}_feature_flag().

Closes: https://github.com/libfuse/libfuse/issues/1171
Signed-off-by: Bernd Schubert <bernd@bsbernd.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/example/hello.c b/example/hello.c
index 6df8173..90919f4 100644
--- a/example/hello.c
+++ b/example/hello.c
@@ -57,6 +57,11 @@ static void *hello_init(struct fuse_conn_info *conn,
 {
 	(void) conn;
 	cfg->kernel_cache = 1;
+
+	/* Test setting flags the old way */
+	conn->want = FUSE_CAP_ASYNC_READ;
+	conn->want &= ~FUSE_CAP_ASYNC_READ;
+
 	return NULL;
 }