userlandfs: implement get_fs_info using ioctl

This avoids introducing an entirely custom hook in FUSE.
It uses the ioctl hook in an unconventional way (calling it with no
valid fuse_file_info) but this can be fixed if a filesystem requires it
(by opening a file handle on /, doing the ioctl, then closing again).

An updated version of fusesmb-haiku is available and confirmed working:
https://github.com/haikuarchives/fusesmb-haiku

Change-Id: If1268113874363fa035e5340be75e9f5198216d6
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5199
Reviewed-by: Adrien Destugues <[email protected]>
Reviewed-by: waddlesplash <[email protected]>
Tested-by: Commit checker robot <[email protected]>

headers/private/userlandfs/fuse/fuse.h

@@ -37,11 +37,6 @@
 extern "C" {
 #endif
 
-#ifdef HAS_FUSE_HAIKU_EXTENSIONS
-struct fs_info;
-extern int gHasHaikuFuseExtensions;
-#endif
-
 
 /* ----------------------------------------------------------- *
  * Basic FUSE API					       *
@@ -459,10 +454,6 @@ struct fuse_operations {
 	 */
 	int (*bmap) (const char *, size_t blocksize, uint64_t *idx);
 
-#ifdef HAS_FUSE_HAIKU_EXTENSIONS
-	int (*get_fs_info) (struct fs_info*);
-#endif
-
 	/**
 	 * Flag indicating that the filesystem can accept a NULL path
 	 * as the first argument for the following operations:
@@ -903,10 +894,6 @@ void fuse_fs_destroy(struct fuse_fs *fs);
 
 int fuse_notify_poll(struct fuse_pollhandle *ph);
 
-#ifdef HAS_FUSE_HAIKU_EXTENSIONS
-int fuse_fs_get_fs_info(struct fuse_fs* fs, struct fs_info* info);
-#endif
-
 /**
  * Create a new fuse filesystem object
  *

headers/private/userlandfs/fuse/fuse_common.h

@@ -113,6 +113,12 @@ struct fuse_file_info {
 #define FUSE_CAP_FLOCK_LOCKS	(1 << 10)
 #define FUSE_CAP_IOCTL_DIR	(1 << 11)
 
+/* Indicate support for Haiku-specific extensions in struct fuse_operations and fuse_ll_ops */
+#define FUSE_CAP_HAIKU_FUSE_EXTENSIONS	(1 << 31)
+
+#define FUSE_HAIKU_GET_DRIVE_INFO (((uint32_t)'H' << 24) | ((uint32_t)'G' << 16) \
+	| ((uint32_t)'D' << 8) | (uint32_t)'I')
+
 /**
  * Ioctl flags
  *