[lustre-devel] [PATCH] xattr handlers: fixup generic_listxattr

[James Simmons]

> generic_listxattr() is different from generic_getxattr() /
> generic_setxattr() / generic_removexattr. It makes sense only for
> filesystems that support a fixed set of xattrs, which means that all
> handlers will have handler->name set.
> 
> If any of the handlers has handler->prefix set instead, that handler
> matches a whole set of attributes. Generic_listxattr() would have to
> fill in all of those names matching that handler, but it doesn't know
> which those are.
> 
> It is common for filesystems to have their own listxattr inode
> operation and still use generic_{get,set,remove}xattr.

That clears things up a bit. So that leaves a few questions. First 
question is looking at several of the file system's implementations
I noticed it contains loops such as:

list_for_each_xattr(entry, base_addr) {
	const struct xattr_handler *handler =                
		blah_xattr_handler(entry->e_name_index);
        const char *prefix;
        size_t prefix_len;
        size_t size;

        if (!handler || (handler->list && !handler->list(dentry)))
        	continue;

	...
}

Is the handler->list() test needed for a private listxattr implementation? 
Also I don't see anyone using handler->list() which which brings up the
next question. What is the purpose of list() function?