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Re: [PATCH RFC] xfs: set block device logical sector size on xfs_buftarg

To: Dave Chinner <david@xxxxxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: [PATCH RFC] xfs: set block device logical sector size on xfs_buftarg
From: Ric Wheeler <rwheeler@xxxxxxxxxx>
Date: Fri, 22 Nov 2013 09:13:56 -0500
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20131114210156.GP6188@dastard>
References: <5283C41D.7070503@xxxxxxxxxx> <20131113185645.GA20869@xxxxxxxxxxxxx> <5283CE2E.2070702@xxxxxxxxxxx> <20131113212658.GJ6188@dastard> <20131114133749.GA26268@xxxxxxxxxxxxx> <5284E484.6090001@xxxxxxxxxxx> <20131114210156.GP6188@dastard>
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On 11/14/2013 04:01 PM, Dave Chinner wrote:
On Thu, Nov 14, 2013 at 08:56:04AM -0600, Eric Sandeen wrote:
On 11/14/13, 7:37 AM, Christoph Hellwig wrote:
On Thu, Nov 14, 2013 at 08:26:58AM +1100, Dave Chinner wrote:
Seems like that's the avenue for improvement here to me. i.e. expose
the correct values to the guest so it's mkfs does the right thing.
Or, alternatively, make qemu buffer non-aligned/sized IOs itself
internally.
I've implemented the support to expose these to the guest in qemu
years ago.  But the problem remains that this is information which
needs to be attached to the image, which can't really work with raw
images, and no one has bother to implement the support to store it
for say qcow2.

Ok but once again - this is not a guest mkfs issue.  The reported
problem is that the guest cannot _boot_ in cache=none mode because
the bios attempts a 512-byte DIO.
A different viewpoint: How can we make sure real 4k sector hardware
works with Linux when it comes along if we can't emulate it via
qemu + virtualisation?

People often use qemu + virutalisation as a method of testing code
for hardware they don't have access to, and this just seems like
another of those things that we should have working in this
environment long before real hardware comes along and requires it...

Cheers,

Dave.

I think you do that by using SCSI debug to get a 4K sector drive - that is how we tested for RHEL6 for example. Layering on restrictions to hardware in the file system seems a bit harsh.

The QEMU crowd will be working to get better support for 4K drives in the future, but I think that we are effectively going to cause a huge field issue here since these 512/4K drives are extremely common..

Given the SCSI debug method for this, does that mean you retract your objections and will support Eric's patch :) ?

Regards,

Ric

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