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, 34 insertions, 0 deletions

diff --git a/lib/fuse_i.h b/lib/fuse_i.h
index bf8410f..23fcaa6 100644
--- a/lib/fuse_i.h
+++ b/lib/fuse_i.h
@@ -8,8 +8,11 @@
 
 #include "fuse.h"
 #include "fuse_lowlevel.h"
+#include "util.h"
 
+#include <stdint.h>
 #include <stdbool.h>
+#include <errno.h>
 
 #define MIN(a, b) \
 ({									\
@@ -224,3 +227,34 @@ int fuse_loop_cfg_verify(struct fuse_loop_config *config);
 /* room needed in buffer to accommodate header */
 #define FUSE_BUFFER_HEADER_SIZE 0x1000
 
+/**
+ * Get the wanted capability flags, converting from old format if necessary
+ */
+static inline int convert_to_conn_want_ext(struct fuse_conn_info *conn,
+					   uint64_t want_ext_default,
+					   uint32_t want_default)
+{
+	/*
+	 * Convert want to want_ext if necessary.
+	 * For the high level interface this function might be called
+	 * twice, once from the high level interface and once from the
+	 * low level interface. Both, with different want_ext_default and
+	 * want_default values. In order to suppress a failure for the
+	 * second call, we check if the lower 32 bits of want_ext are
+	 * already set to the value of want.
+	 */
+	if (conn->want != want_default &&
+	    fuse_lower_32_bits(conn->want_ext) != conn->want) {
+		if (conn->want_ext != want_ext_default) {
+			fuse_log(FUSE_LOG_ERR,
+				 "fuse: both 'want' and 'want_ext' are set\n");
+			return -EINVAL;
+		}
+
+		/* high bits from want_ext, low bits from want */
+		conn->want_ext = fuse_higher_32_bits(conn->want_ext) |
+				 conn->want;
+	}
+
+	return 0;
+}