# Re: \[PATCH RESEND x3 v9 1/9\] iov\_iter: add copy\_struct\_from\_iter()

- From: Matthew Wilcox \<willy@infradead.org\>
- Date: 2021-06-25 03:38:30 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2021/06/208734
- Thread: https://ratatoskr.run/linux-fsdevel/2021/06/208723/t.md

```text
On Thu, Jun 24, 2021 at 06:41:52PM -0400, Martin K. Petersen wrote:
> 
> Linus,
> 
> > I also worry that this "raw compressed data" thing isn't the only
> > thing people will want to do. I could easily see some kind of
> > "end-to-end CRC read/write" where the user passes in not just the
> > data, but also checksums for it to validate it (maybe because you're
> > doing a file copy and had the original checksums, but also maybe
> > because user space simply has a known good copy and doesn't want
> > errors re-introduced due to memory corruption).
> 
> We already support passing CRCs down to be validated by the hardware for
> both NVMe and SCSI. This currently only works from the block layer
> down. When enabled, the checksums are generated by the block layer for
> writes and the data is validated against the checksums sent by the
> storage on reads.
> 
> Over the years various attempts at adding support for passing the
> checksum buffers in from userland have failed for exactly the reasons
> outlined in this thread (Joel, Darrick, Bob). Would love to have a
> generic way of passing this kind of information...

Does it make any kind of sense to talk about doing this for buffered I/O,
given that we can't generate them for (eg) mmaped files?  Or does this
only make sense to pass in for O_DIRECT accesses?
```