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Re: NVMe ZNS zone append past zone size?

From: Klaus Jensen
Subject: Re: NVMe ZNS zone append past zone size?
Date: Tue, 19 Jan 2021 12:19:01 +0100

On Jan 19 10:38, Niklas Cassel wrote:
> Hello all,
> When testing with the ZNS code that is in nvme-next,
> I can zone append, targeting the first zone by specifying zslba 0,
> and then just put that call it in a while loop, it will
> manage to fill up not just zone0, but the whole drive.
> Since zslba is defined as:
> "Zone Start Logical Block Address (ZSLBA): This field indicates the 64-bit
> address of the lowest logical block of the zone in which the data and
> metadata, if applicable, associated with this command is to be stored."
> Should an append that specifies zslba 0 (== zone 0), be allowed
> to write into zone 1 (and beyond).
> According to "Writing in Sequential Write Required Zones",
> we should get either a "Zone Boundary Error" or "Zone Is Full" error,
> depending on zone 0 write pointer, combined with how many LBAs we try
> to append.
> Looking at the code, I think that this has to be handled in
> either nvme_check_zone_write() or nvme_advance_zone_wp().
> Considering that Dmitry and Klaus were discussing when to advance
> the write pointer, etc, for several of the patch series revisions,
> I think it is better to leave a potential fix to you guys.


The reason we're not getting a zone boundary error is because the
boundary condition is checked before assigning an LBA, so we always
check against ZSLBA.

I can see that in my old branch I'm checking the write *after* assigning
the SLBA, so it didn't exhibity that behavior. I'll draw up a fix based
on that.

Thanks Niklas!

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