linux-kernel - Re: [RFC PATCH 33/33] Add Xen virtual block device driver.

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Message-Id: <1153218847.3038.52.camel@laptopd505.fenrus.org>
Date:	Tue, 18 Jul 2006 12:34:06 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com,
	Jeremy Fitzhardinge <jeremy@...p.org>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...l.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zachary Amsden <zach@...are.com>,
	Ian Pratt <ian.pratt@...source.com>,
	Christian Limpach <Christian.Limpach@...cam.ac.uk>
Subject: Re: [RFC PATCH 33/33] Add Xen virtual block device driver.

On Tue, 2006-07-18 at 00:00 -0700, Chris Wright wrote:
> plain text document attachment (blkfront)
> The block device frontend driver allows the kernel to access block
> devices exported exported by a virtual machine containing a physical
> block device driver.

Hi,

as first general comment, I think that some of the memory allocation
GFP_ flags are possibly incorrect; I would expect several places to use
GFP_NOIO rather than GFP_KERNEL, to avoid recursion/deadlocks

> +static void blkif_recover(struct blkfront_info *info)
> +{
> +	int i;
> +	struct blkif_request *req;
> +	struct blk_shadow *copy;
> +	int j;
> +
> +	/* Stage 1: Make a safe copy of the shadow state. */
> +	copy = kmalloc(sizeof(info->shadow), GFP_KERNEL | __GFP_NOFAIL);

like here..

> +	memcpy(copy, info->shadow, sizeof(info->shadow));

and __GFP_NOFAIL is usually horrid; is this because error recovery was
an afterthought, or because it's physically impossible? In addition
__GFP_NOFAIL in a block device driver is... an interesting way to add
OOM deadlocks... have the VM guys looked into this yet?

> +#if 1
> +#define IPRINTK(fmt, args...) \
> +    printk(KERN_INFO "xen_blk: " fmt, ##args)
> +#else
> +#define IPRINTK(fmt, args...) ((void)0)
> +#endif

hmm isn't this a duplication of the pr_debug() and dev_dbg()
infrastructure? Please don't reinvent new ones..




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