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Date: Wed, 23 Apr 2025 09:05:48 -0600
From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Leon Romanovsky <leon@kernel.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Jens Axboe <axboe@kernel.dk>, Jake Edge <jake@lwn.net>,
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	Zhu Yanjun <zyjzyj2000@gmail.com>,
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	Will Deacon <will@kernel.org>, Sagi Grimberg <sagi@grimberg.me>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Logan Gunthorpe <logang@deltatee.com>,
	Yishai Hadas <yishaih@nvidia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	=?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
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	Chaitanya Kulkarni <kch@nvidia.com>,
	Nitesh Shetty <nj.shetty@samsung.com>,
	Leon Romanovsky <leonro@nvidia.com>
Subject: Re: [PATCH v9 23/24] nvme-pci: convert to blk_rq_dma_map
Message-ID: <aAkBzDgjiWkbeP8P@kbusch-mbp.dhcp.thefacebook.com>
References: <cover.1745394536.git.leon@kernel.org>
 <7c5c5267cba2c03f6650444d4879ba0d13004584.1745394536.git.leon@kernel.org>
 <20250423092437.GA1895@lst.de>
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In-Reply-To: <20250423092437.GA1895@lst.de>

On Wed, Apr 23, 2025 at 11:24:37AM +0200, Christoph Hellwig wrote:
> Right now I don't have a test setup for metasgl, though.  Keith,
> do you have a good qemu config for that?  Or anyone else?

QEMU does support it, and reports support for it by default (you may
need to upgrade qemu if yours is more than a year old). You just need to
format your namespace with metadata then you can send commands with
either SGL or MPTR.

QEMU supports 0, 8, 16, and 64 metadata bytes on either 512b or 4k block
sizes.

If you want 8 bytes for metadata on start up, attach parameter "ms=8" to
the '-device nvme-ns' qemu setup.

Alternatively, you can use the 'nvme format' command after booting to
change it whenever you want.