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Date: Tue, 14 Jul 2015 00:15:37 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Kinglong Mee <kinglongmee@gmail.com>
Cc: Steve Dickson <SteveD@redhat.com>, Christoph Hellwig <hch@infradead.org>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v3] blkmapd: Skip the SCSI ID if data length is zero
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> +		/* Needs an SCSI ID with unique date not zero length */
> +		if (!dev_id->len)
> +			continue;

That explains what the code does, not why it does so.

How about:

		/*
		 * Some buggy targets (e.g. VMWare) export zero length
		 * EVPD pages, skip them to not confuse the device id
		 * cache.
		 */