pseudofs: add support for export_ops

Pseudo-filesystems might reasonably wish to implement the export ops
(particularly for name_to_handle_at/open_by_handle_at); plumb this
through pseudo_fs_context

Reviewed-by: Amir Goldstein <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Erin Shepherd <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: erincandescent

fs/libfs.c

@@ -673,6 +673,7 @@ static int pseudo_fs_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_blocksize_bits = PAGE_SHIFT;
 	s->s_magic = ctx->magic;
 	s->s_op = ctx->ops ?: &simple_super_operations;
+	s->s_export_op = ctx->eops;
 	s->s_xattr = ctx->xattr;
 	s->s_time_gran = 1;
 	root = new_inode(s);

include/linux/pseudo_fs.h

@@ -5,6 +5,7 @@
 
 struct pseudo_fs_context {
 	const struct super_operations *ops;
+	const struct export_operations *eops;
 	const struct xattr_handler * const *xattr;
 	const struct dentry_operations *dops;
 	unsigned long magic;