linux-kernel - Re: Generic infrastructure for acls

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Message-Id: <200609020032.02595.agruen@suse.de>
Date:	Sat, 2 Sep 2006 00:32:02 +0200
From:	Andreas Gruenbacher <agruen@...e.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel@...r.kernel.org, James Morris <jmorris@...ei.org>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: Generic infrastructure for acls

On Friday, 01 September 2006 23:44, Andrew Morton wrote:
> On Sat, 02 Sep 2006 00:14:22 +0200
>
> Andreas Gruenbacher <agruen@...e.de> wrote:
> > +generic_acl_list(struct inode *inode, struct generic_acl_operations
> > *ops, +		 int type, char *list, size_t list_size)
> > +{
> > +	struct posix_acl *acl;
> > +	const char *name;
> > +	size_t size;
> > +
> > +	acl = ops->getacl(inode, type);
> > +	if (!acl)
> > +		return 0;
> > +	posix_acl_release(acl);
> > +
> > +	switch(type) {
> > +		case ACL_TYPE_ACCESS:
> > +			name = POSIX_ACL_XATTR_ACCESS;
> > +			break;
> > +
> > +		case ACL_TYPE_DEFAULT:
> > +			name = POSIX_ACL_XATTR_DEFAULT;
> > +			break;
> > +
> > +		default:
> > +			return 0;
> > +	}
> > +	size = strlen(name) + 1;
> > +	if (list && size <= list_size)
> > +		memcpy(list, name, size);
> > +	return size;
> > +}
>
> That's a clumsy-looking interface.

We could get rid of the switch by passing in the type and the name, but 
otherwise that's pretty exactly what's needed, no matter if done in a 
fs-dependent or independent way.

> How is the caller to know that *list got filled in? By checking the 
generic_acl_list() return value against `list_size'?

The return value determines how many bytes have been used or would be needed 
in the buffer -- generic_listxattr() in fs/xattr.c has this code:

> for_each_xattr_handler(handlers, handler) {
>     size = handler->list(inode, buf, buffer_size, NULL, 0);
>     if (size > buffer_size) 
>         return -ERANGE;
>     buf += size;
>     buffer_size -= size;
> }

Andreas

-- 
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