ANDROID: fuse-bpf: Add /sys/fs flags for fuse-bpf version

Note that this is specific for the non-upstreamed version

Bug: 202785178
Test: cat /sys/fs/fuse/fuse_bpf_major_version
Change-Id: I68f9ca56778874975428839dfc1fd8f48b11bd75
Signed-off-by: Paul Lawrence <paullawrence@google.com>

Documentation/ABI/testing/sysfs-fs-fuse

@@ -0,0 +1,19 @@
+What:		/sys/fs/fuse/features/fuse_bpf
+Date:		December 2022
+Contact:	Paul Lawrence <paullawrence@google.com>
+Description:
+		Read-only file that contains the word 'supported' if fuse-bpf is
+		supported, does not exist otherwise
+
+What:		/sys/fs/fuse/bpf_prog_type_fuse
+Date:		December 2022
+Contact:	Paul Lawrence <paullawrence@google.com>
+Description:
+		bpf_prog_type_fuse defines the program type of bpf programs that
+		may be passed to fuse-bpf. For upstream bpf program types, this
+		is a constant defined in a contiguous array of constants.
+		bpf_prog_type_fuse is appended to the end of the list, so it may
+		change and therefore its value must be read from this file.
+
+		Contents is ASCII decimal representation of bpf_prog_type_fuse
+

fs/fuse/inode.c

@@ -2027,7 +2027,31 @@ static void fuse_fs_cleanup(void)
 
 static struct kobject *fuse_kobj;
 
-/* TODO Remove this once BPF_PROG_TYPE_FUSE is upstreamed */
+static ssize_t fuse_bpf_show(struct kobject *kobj,
+				       struct kobj_attribute *attr, char *buff)
+{
+	return sysfs_emit(buff, "supported\n");
+}
+
+static struct kobj_attribute fuse_bpf_attr =
+		__ATTR_RO(fuse_bpf);
+
+static struct attribute *bpf_features[] = {
+	&fuse_bpf_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group bpf_features_group = {
+	.name = "features",
+	.attrs = bpf_features,
+};
+
+/*
+ * TODO Remove this once fuse-bpf is upstreamed
+ *
+ * bpf_prog_type_fuse exports the bpf_prog_type_fuse 'constant', which cannot be
+ * constant until the code is upstreamed
+ */
 static ssize_t bpf_prog_type_fuse_show(struct kobject *kobj,
 				       struct kobj_attribute *attr, char *buff)
 {
@@ -2045,6 +2069,13 @@ static struct attribute *bpf_attributes[] = {
 static const struct attribute_group bpf_attr_group = {
 	.attrs = bpf_attributes,
 };
+
+static const struct attribute_group *attribute_groups[] = {
+	&bpf_features_group,
+	&bpf_attr_group,
+	NULL
+};
+
 /* TODO remove to here */
 
 static int fuse_sysfs_init(void)
@@ -2062,7 +2093,7 @@ static int fuse_sysfs_init(void)
 		goto out_fuse_unregister;
 
 	/* TODO Remove when BPF_PROG_TYPE_FUSE is upstreamed */
-	err = sysfs_create_group(fuse_kobj, &bpf_attr_group);
+	err = sysfs_create_groups(fuse_kobj, attribute_groups);
 	if (err)
 		goto out_fuse_remove_mount_point;
 
@@ -2078,6 +2109,7 @@ static int fuse_sysfs_init(void)
 
 static void fuse_sysfs_cleanup(void)
 {
+	sysfs_remove_groups(fuse_kobj, attribute_groups);
 	sysfs_remove_mount_point(fuse_kobj, "connections");
 	kobject_put(fuse_kobj);
 }