btrfs: retrieve more info from FS_INFO ioctl

Provide the basic information about filesystem through the ioctl:
* b-tree node size (same as leaf size)
* sector size
* expected alignment of CLONE_RANGE and EXTENT_SAME ioctl arguments

Backward compatibility: if the values are 0, kernel does not provide
this information, the applications should ignore them.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ioctl.c

@@ -2574,6 +2574,10 @@ static long btrfs_ioctl_fs_info(struct btrfs_root *root, void __user *arg)
 	}
 	mutex_unlock(&fs_devices->device_list_mutex);
 
+	fi_args->nodesize = root->fs_info->super_copy->nodesize;
+	fi_args->sectorsize = root->fs_info->super_copy->sectorsize;
+	fi_args->clone_alignment = root->fs_info->super_copy->sectorsize;
+
 	if (copy_to_user(arg, fi_args, sizeof(*fi_args)))
 		ret = -EFAULT;
 

include/uapi/linux/btrfs.h

@@ -181,7 +181,11 @@ struct btrfs_ioctl_fs_info_args {
 	__u64 max_id;				/* out */
 	__u64 num_devices;			/* out */
 	__u8 fsid[BTRFS_FSID_SIZE];		/* out */
-	__u64 reserved[124];			/* pad to 1k */
+	__u32 nodesize;				/* out */
+	__u32 sectorsize;			/* out */
+	__u32 clone_alignment;			/* out */
+	__u32 reserved32;
+	__u64 reserved[122];			/* pad to 1k */
 };
 
 struct btrfs_ioctl_feature_flags {