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, 29 insertions, 4 deletions

diff --git a/lib/fuse.c b/lib/fuse.c
index 9335429..136f0c2 100644
--- a/lib/fuse.c
+++ b/lib/fuse.c
@@ -10,6 +10,8 @@
 */
 
 #define _GNU_SOURCE
+#include "fuse.h"
+#include <pthread.h>
 
 #include "fuse_config.h"
 #include "fuse_i.h"
@@ -17,7 +19,9 @@
 #include "fuse_opt.h"
 #include "fuse_misc.h"
 #include "fuse_kernel.h"
+#include "util.h"
 
+#include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -2606,13 +2610,34 @@ void fuse_fs_init(struct fuse_fs *fs, struct fuse_conn_info *conn,
 {
 	fuse_get_context()->private_data = fs->user_data;
 	if (!fs->op.write_buf)
-		conn->want &= ~FUSE_CAP_SPLICE_READ;
+		fuse_unset_feature_flag(conn, FUSE_CAP_SPLICE_READ);
 	if (!fs->op.lock)
-		conn->want &= ~FUSE_CAP_POSIX_LOCKS;
+		fuse_unset_feature_flag(conn, FUSE_CAP_POSIX_LOCKS);
 	if (!fs->op.flock)
-		conn->want &= ~FUSE_CAP_FLOCK_LOCKS;
-	if (fs->op.init)
+		fuse_unset_feature_flag(conn, FUSE_CAP_FLOCK_LOCKS);
+	if (fs->op.init) {
+		uint64_t want_ext_default = conn->want_ext;
+		uint32_t want_default = fuse_lower_32_bits(conn->want_ext);
+		int rc;
+
+		conn->want = want_default;
 		fs->user_data = fs->op.init(conn, cfg);
+
+		rc = convert_to_conn_want_ext(conn, want_ext_default,
+					      want_default);
+
+		if (rc != 0) {
+			/*
+			 * This is a grave developer error, but
+			 * we cannot return an error here, as the function
+			 * signature does not allow it.
+			 */
+			fuse_log(
+				FUSE_LOG_ERR,
+				"fuse: Aborting due to invalid conn want flags.\n");
+			_exit(EXIT_FAILURE);
+		}
+	}
 }
 
 static int fuse_init_intr_signal(int signum, int *installed);