On Thu, Feb 07, 2013 at 02:09:17PM -0500, Martin K. Petersen wrote:
> >>>>> "Darrick" == Darrick J Wong <darrick.wong@xxxxxxxxxx> writes:
>
> Darrick> and more recently I've theorized that we could add a magic
> Darrick> fcntl/ioctl to make the kernel recognize, say, the first iovec
> Darrick> of a O_DIRECT *{read,write}v call as the PI buffer, which I
> Darrick> think is similar to how DIX gets PI data to a disk. But it's
> Darrick> not like I have any code to show for it.
>
> I don't particularly like the "stick it in the first iovec" magic. Also,
> we need a bit more than this. A handful of knobs need to be present to
> convey how the PI should be sliced and diced. So then we get into the
> territory where the first iovec is a PI descriptor of some sort. And
> then the second entry is the PI buffer.
Hm, well if we're adding another IO_CMD_ anyway, it probably isn't that hard to
find space to stuff in an extra pointer or two to a PI descriptor + buffer.
(or a pointer to a descriptor that itself points to a buffer...)
> Darrick> I /think/ it's fairly straightforward to change the directio
> Darrick> submit code to find the userspace PI buffer and amend the block
> Darrick> integrity code to attach our own PI buffer.
>
> I recommend that you check out how I do this in oracleasm.
Is there a newer one than this?
https://oss.oracle.com/projects/oracleasm/files/sources/
(Nov. 2008?)
>
> Darrick> You'd still have to let the block layer set the sector # field,
> Darrick> but afaik that won't affect the crc or the app tag.
>
> Correct. But the right way would be to pass the ref tag seed in as part
> of the IOCB and let sd or the HBA hardware do the remapping.
<nod>
--D
>
> --
> Martin K. Petersen Oracle Linux Engineering
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