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Subject: Re: [Xen-devel] [PATCH] xen-blkback: prefer xenbus_write() over
 xenbus_printf() where possible
To: David Vrabel <david.vrabel@citrix.com>, Jan Beulich <JBeulich@suse.com>,
        Roger Pau Monne <roger.pau@citrix.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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 <577E2E3A.60803@citrix.com>
CC: <xen-devel@lists.xenproject.org>, <linux-kernel@vger.kernel.org>
From: David Vrabel <david.vrabel@citrix.com>
Message-ID: <577E324E.9000808@citrix.com>
Date: Thu, 7 Jul 2016 11:43:26 +0100
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On 07/07/16 11:26, David Vrabel wrote:
> On 07/07/16 09:06, Jan Beulich wrote:
>> ... as being the simpler variant.
> [...]
>> --- 4.7-rc6-prefer-xenbus_write.orig/drivers/block/xen-blkback/xenbus.c
>> +++ 4.7-rc6-prefer-xenbus_write/drivers/block/xen-blkback/xenbus.c
>> @@ -617,9 +617,9 @@ static int xen_blkbk_probe(struct xenbus
>>  		goto fail;
>>  	}
>>  
>> -	err = xenbus_printf(XBT_NIL, dev->nodename,
>> -			    "feature-max-indirect-segments", "%u",
>> -			    MAX_INDIRECT_SEGMENTS);
>> +	err = xenbus_write(XBT_NIL, dev->nodename,
>> +			   "feature-max-indirect-segments",
>> +			   __stringify(MAX_INDIRECT_SEGMENTS));
> 
> Yuk :(
> 
> Now someone has to check both __stringify() and MAX_INDIRECT_SEGMENTS to
> work out what this actually looks like.

In particular, if we ended up with

#define MAX_INDIRECT_SEGMENTS 512u

or similar then the code is now wrong.

David