linux-kernel - Re: [Xen-devel] [PATCH v2] xen-blkfront: remove type check from blkfront_setup

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Message-Id: <52D3DAEE0200007800112FD4@nat28.tlf.novell.com>
Date:	Mon, 13 Jan 2014 11:24:14 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Olaf Hering" <olaf@...fle.de>
Cc:	<david.vrabel@...rix.com>, <xen-devel@...ts.xen.org>,
	<boris.ostrovsky@...cle.com>, <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH v2] xen-blkfront: remove type check
 from blkfront_setup_discard

>>> On 13.01.14 at 11:14, Olaf Hering <olaf@...fle.de> wrote:
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -1634,37 +1634,22 @@ blkfront_closing(struct blkfront_info *info)
>  
>  static void blkfront_setup_discard(struct blkfront_info *info)
>  {
> -	int err;
> -	char *type;
>  	unsigned int discard_granularity;
>  	unsigned int discard_alignment;
>  	unsigned int discard_secure;
>  
> -	type = xenbus_read(XBT_NIL, info->xbdev->otherend, "type", NULL);
> -	if (IS_ERR(type))
> +	if (xenbus_gather(XBT_NIL, info->xbdev->otherend,
> +		"discard-granularity", "%u", &discard_granularity,
> +		"discard-alignment", "%u", &discard_alignment,
> +		"discard-secure", "%u", &discard_secure,
> +		NULL))
>  		return;

You can't do this in one go - the first two and the last one may be
set independently (and are independent in their meaning), and
hence need to be queried independently (xenbus_gather() fails
on the first absent value).

Jan

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