Re: [PATCH 7/7] xfs: implement block-metadata based data checksums

[Christoph Hellwig <hch@lst.de>]

On Mon, Feb 03, 2025 at 02:20:31PM -0800, Darrick J. Wong wrote:
> On Mon, Feb 03, 2025 at 10:43:11AM +0100, Christoph Hellwig wrote:
> > This is a quick hack to demonstrate how data checksumming can be
> > implemented when it can be stored in the out of line metadata for each
> > logical block.  It builds on top of the previous PI infrastructure
> > and instead of generating/verifying protection information it simply
> > generates and verifies a crc32c checksum and stores it in the non-PI
> 
> PI can do crc32c now?  I thought it could only do that old crc16 from
> like 15 years ago and crc64?

NVMe has a protection information format with a crc32c, but it's not
supported by Linux yet.

> If we try to throw crc32c at a device,
> won't it then reject the "incorrect" checksums?  Or is there some other
> magic in here where it works and I'm just too out of date to know?

This patch implements XFS-level data checksums on devices that implement
non-PI metadata, that is the device allows to store extra data with the
LBA, but doesn't actually interpret and verify it іn any way.

> The crc32c generation and validation looks decent though we're
> definitely going to want an inode flag so that we're not stuck with
> stable page writes.

Yeah, support the NOCOW flag, have a sb flag to enable the checksums,
maybe even a field about what checksum to use, yodda, yodda.