ANDROID: fs/fuse: Use extended init flags for FUSE_PASSTHROUGH

Starting with FUSE 7.36, all the fields for the 32-bit FUSE init flags
have been allocated, so commit 53db28933e ("fuse: extend init flags")
introduces the new 32-bit flags2 field in fuse_init_in and
fuse_init_out. That change also adds the FUSE_INIT_RESERVED flag that
doesn't have any specific purpose yet, is just reserved and should not
be used, and (un)fortunately collides with FUSE_PASSTHROUGH.

This change fixes the conflict by simply setting the FUSE_PASSTHROUGH
value to the next, latest unused fuse2 bit.
Although this is not the best design choice, userspace will know what
FUSE_PASSTHROUGH bit to choose based on the FUSE major and minor version
for FUSE version:
- < 7.36:    FUSE_PASSTHROUGH is the 31st bit of flags;
- otherwise: FUSE_PASSTHROUGH is the 31st bit of flags2.

Test: launch_cvd (both android-mainline and android13-5.10) \
  `logcat FuseDaemon:V \*:S` shows no FUSE passthrough errors
Bug: 215310351
Signed-off-by: Alessio Balsini <balsini@google.com>
Change-Id: I85d7582008b8c093b3172b3f41c6cdf09863dd45

fs/fuse/inode.c

@@ -1227,7 +1227,6 @@ void fuse_send_init(struct fuse_mount *fm)
 		FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL |
 		FUSE_ABORT_ERROR | FUSE_MAX_PAGES | FUSE_CACHE_SYMLINKS |
 		FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA |
-		FUSE_PASSTHROUGH |
 		FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_EXT;
 #ifdef CONFIG_FUSE_DAX
 	if (fm->fc->dax)
@@ -1236,6 +1235,8 @@ void fuse_send_init(struct fuse_mount *fm)
 	if (fm->fc->auto_submounts)
 		ia->in.flags |= FUSE_SUBMOUNTS;
 
+	ia->in.flags |= FUSE_PASSTHROUGH;
+
 	ia->args.opcode = FUSE_INIT;
 	ia->args.in_numargs = 1;
 	ia->args.in_args[0].size = sizeof(ia->in);

include/uapi/linux/fuse.h

@@ -372,7 +372,18 @@ struct fuse_file_lock {
 #define FUSE_SUBMOUNTS		(1 << 27)
 #define FUSE_HANDLE_KILLPRIV_V2	(1 << 28)
 #define FUSE_SETXATTR_EXT	(1 << 29)
-#define FUSE_PASSTHROUGH	(1 << 31)
+
+/*
+ * For FUSE < 7.36 FUSE_PASSTHROUGH has value (1 << 31).
+ * This condition check is not really required, but would prevent having a
+ * broken commit in the tree.
+ */
+#if FUSE_KERNEL_VERSION > 7 ||                                                 \
+	(FUSE_KERNEL_VERSION == 7 && FUSE_KERNEL_MINOR_VERSION >= 36)
+#define FUSE_PASSTHROUGH (1ULL << 63)
+#else
+#define FUSE_PASSTHROUGH (1 << 31)
+#endif
 
 /**
  * CUSE INIT request/reply flags