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Date:   Wed, 26 Feb 2020 16:07:06 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Dave Chinner <david@fromorbit.com>
Cc:     Christoph Hellwig <hch@lst.de>, linux-xfs@vger.kernel.org,
        Chandan Rajendra <chandanrlinux@gmail.com>,
        "Darrick J . Wong" <darrick.wong@oracle.com>
Subject: Re: [PATCH 10/30] xfs: pass an initialized xfs_da_args structure
 to xfs_attr_set
Message-ID: <20200226150706.GA19599@lst.de>
References: <20200225231012.735245-1-hch@lst.de> <20200225231012.735245-11-hch@lst.de> <20200226002109.GS10776@dread.disaster.area>
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On Wed, Feb 26, 2020 at 11:21:09AM +1100, Dave Chinner wrote:
> >  		/* subtract away the unused acl entries */
> > -		len -= sizeof(struct xfs_acl_entry) *
> > +		args.valuelen -= sizeof(struct xfs_acl_entry) *
> >  			 (XFS_ACL_MAX_ENTRIES(ip->i_mount) - acl->a_count);
> 
> why do we allocate a maximally sized buffer for the attribute data
> (64kB for v5 filesystems) when we already know the size of the
> data we are about to format into it? Why isn't this just:
> 
> 	if (acl) {
> 		args.valuelen = sizeof(struct xfs_acl_entry) * acl->a_count;
> 		args.value = kmem_zalloc_large(args.valuelen, 0);
> 		if (!args.value)
> 			return -ENOMEM;
> 
> 		xfs_acl_to_disk(args.value, acl); 
> 	}

We need to also account for the size of the acl header, and have the
XFS_ACL_SIZE macro to do so. But with that it makes sense, and I've
added a patch to do so to the end of the series.