linux-kernel - Re: [PATCH] SCSI: Add SG_GET_SG_MAX_SEGMENT

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Date:	Tue, 03 Jul 2012 15:53:23 +0800
From:	Cong Meng <mc@...ux.vnet.ibm.com>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	stefanha@...ux.vnet.ibm.com, linuxram@...ibm.com,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	senwang@...ux.vnet.ibm.com
Subject: Re: [PATCH] SCSI: Add SG_GET_SG_MAX_SEGMENT_SIZE ioctl to sg device

On Mon, 2012-07-02 at 12:18 +0100, James Bottomley wrote:
> On Mon, 2012-07-02 at 17:20 +0800, Cong Meng wrote:
> > Add a new ioctl cmd to get the max segment size. It's useful in
> > virtualization environment for guest to know the queue limits, so
> > that the guest kicks off legal scsi command to a sg device.
> 
> What's wrong with simply looking in the /sys for this? Plus, if you can

Adding this ioctl is a big convenience for the programs, qemu 
in my case, to which parameter that likes '/dev/sgX' is given. 
With this ioctl, those programs only need to issue an ioctl to 
get the queue limit. Otherwise, 'dev/sgX' is needed to convert 
to /sys path, then open and read it. 
In addition, the potential variation and exceptional situation 
of sys FS, EX mount path, are needed to consider as well.
Is my justification acceptable? 

> come up with a justifiable reason, this needs to be in block as well so
> we can send it to all SCSI devices regardless of what ULD people use.
I can do it.

Thanks.
Cong.
> 
> James
> 
> 


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