freevxfs: derive f_fsid from bdev->bd_dev

The majority of blockdev filesystems, which do not have a UUID in their
on-disk format, derive f_fsid of statfs(2) from bdev->bd_dev.

Use the same practice for freevxfs.

This will allow reporting fanotify events with fanotify_event_info_fid.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20231024121457.3014063-1-amir73il@gmail.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/freevxfs/vxfs_super.c

@@ -76,6 +76,7 @@ vxfs_statfs(struct dentry *dentry, struct kstatfs *bufp)
 {
 	struct vxfs_sb_info		*infp = VXFS_SBI(dentry->d_sb);
 	struct vxfs_sb *raw_sb = infp->vsi_raw;
+	u64 id = huge_encode_dev(dentry->d_sb->s_bdev->bd_dev);
 
 	bufp->f_type = VXFS_SUPER_MAGIC;
 	bufp->f_bsize = dentry->d_sb->s_blocksize;
@@ -84,6 +85,7 @@ vxfs_statfs(struct dentry *dentry, struct kstatfs *bufp)
 	bufp->f_bavail = 0;
 	bufp->f_files = 0;
 	bufp->f_ffree = fs32_to_cpu(infp, raw_sb->vs_ifree);
+	bufp->f_fsid = u64_to_fsid(id);
 	bufp->f_namelen = VXFS_NAMELEN;
 
 	return 0;