linux-kernel - Re: [RFC v3] qemu: Add virtio pmem device

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Message-ID: <783786ae-2e85-2376-448c-1e362c3d4d48@redhat.com>
Date:   Tue, 24 Jul 2018 11:13:07 -0500
From:   Eric Blake <eblake@...hat.com>
To:     Pankaj Gupta <pagupta@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, qemu-devel@...gnu.org,
        linux-nvdimm@...1.01.org
Cc:     jack@...e.cz, stefanha@...hat.com, dan.j.williams@...el.com,
        riel@...riel.com, haozhong.zhang@...el.com, nilal@...hat.com,
        kwolf@...hat.com, pbonzini@...hat.com, ross.zwisler@...el.com,
        david@...hat.com, xiaoguangrong.eric@...il.com, hch@...radead.org,
        mst@...hat.com, niteshnarayanlal@...mail.com,
        lcapitulino@...hat.com, imammedo@...hat.com
Subject: Re: [RFC v3] qemu: Add virtio pmem device

On 07/13/2018 02:52 AM, Pankaj Gupta wrote:
>   This patch adds virtio-pmem Qemu device.
> 
>   This device presents memory address range information to guest
>   which is backed by file backend type. It acts like persistent
>   memory device for KVM guest. Guest can perform read and persistent
>   write operations on this memory range with the help of DAX capable
>   filesystem.
> 
>   Persistent guest writes are assured with the help of virtio based
>   flushing interface. When guest userspace space performs fsync on
>   file fd on pmem device, a flush command is send to Qemu over VIRTIO
>   and host side flush/sync is done on backing image file.
> 
> Changes from RFC v2:

This patch has no n/M in the subject line; but is included in a thread 
that also has a 0/2 cover letter, as well as 1/2 and 2/2 patches in 
separate mails.  Is that intentional?

When sending revision notes on a specific patch, it's best to place them...

> - Use aio_worker() to avoid Qemu from hanging with blocking fsync
>    call - Stefan
> - Use virtio_st*_p() for endianess - Stefan
> - Correct indentation in qapi/misc.json - Eric
> 
> Signed-off-by: Pankaj Gupta <pagupta@...hat.com>
> ---

...here, after the --- separator. They are useful to reviewers on the 
list, but are stripped by 'git am' as they don't need to be part of the 
git history (a year from now, we won't care how many iterations the 
patch went through during review, only what actually landed).


> +++ b/qapi/misc.json
> @@ -2907,6 +2907,29 @@
>             }
>   }
>   
> +##
> +# @VirtioPMemDeviceInfo:
> +#
> +# VirtioPMem state information
> +#
> +# @id: device's ID
> +#
> +# @start: physical address, where device is mapped
> +#
> +# @size: size of memory that the device provides
> +#
> +# @memdev: memory backend linked with device
> +#
> +# Since: 2.13

There is no 2.13 release, and you've missed the 3.0 window.  Please 
update this and any other version reference to 3.1.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org