Re: [PATCH 1/2] nvme: make independent ns identify default

[Matias Bjørling]

On 09-10-2024 08:16, Hannes Reinecke wrote:
> On 10/8/24 16:55, Matias Bjørling wrote:
> > From: Matias Bjørling <matias.bjorling@xxxxxxx>
> >
> > The NVMe 2.0 specification adds an independent identify namespace
> > data structure that contains generic attributes that apply to all
> > namespace types. Some attributes carry over from the NVM command set
> > identify namespace data structure, and others are new.
> >
> > Currently, the data structure only considered when CRIMS is enabled or
> > when the namespace type is key-value.
> >
> > However, the independent namespace data structure
> > is mandatory for devices that implement features from the 2.0+
> > specification. Therefore, we can check this data structure first. If
> > unavailable, retrieve the generic attributes from the NVM command set
> > identify namespace data structure.
> >
> > Signed-off-by: Matias Bjørling <matias.bjorling@xxxxxxx>
> > ---
> >   drivers/nvme/host/core.c | 7 +++----
> >   1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> > index 0dc8bcc664f2..9cbef6342c39 100644
> > --- a/drivers/nvme/host/core.c
> > +++ b/drivers/nvme/host/core.c
> > @@ -3999,7 +3999,7 @@ static void nvme_scan_ns(struct nvme_ctrl *ctrl, 
> > unsigned nsid)
> >   {
> >       struct nvme_ns_info info = { .nsid = nsid };
> >       struct nvme_ns *ns;
> > -    int ret;
> > +    int ret = 1;
> >       if (nvme_identify_ns_descs(ctrl, &info))
> >           return;
> > @@ -4015,10 +4015,9 @@ static void nvme_scan_ns(struct nvme_ctrl 
> > *ctrl, unsigned nsid)
> >        * data structure to find all the generic information that is 
> > needed to
> >        * set up a namespace.  If not fall back to the legacy version.
> >        */
> > -    if ((ctrl->cap & NVME_CAP_CRMS_CRIMS) ||
> > -        (info.ids.csi != NVME_CSI_NVM && info.ids.csi != NVME_CSI_ZNS))
> > +    if (!nvme_ctrl_limited_cns(ctrl))
> >           ret = nvme_ns_info_from_id_cs_indep(ctrl, &info);
> > -    else
> > +    if (ret > 0)
> >           ret = nvme_ns_info_from_identify(ctrl, &info);
> >       if (info.is_removed)
>
> That is a very odd coding. 'info' will only be filled out for a non-zero
> return value of nvme_ns_info_from_cs_indep().

I may have misunderstood. Only if nvme_ns_info_from_cs_indep() return 0 
will the information be filled. Otherwise, if it is an NVMe error, 
nvme_ns_info_from_identify() is tried, otherwise it's a hard error, and 
it errors out completely.

> So why not check for that?
> But if we get an NVME status back there is a fair chance that something 
> else than 'invalid field' (or whatever indicated that the command is not 
> supported). That then would cause the device to be misdetected without 
> the admin knowning.
> Shouldn't we add a message if we fall back to nvme_ns_info_from_identify()?

Hmm, we could. Buuuut, at this point, there's more devices falling back 
to nvme_ns_info_from_identify(), than devices that implements the 
independent ns identify data structure. So I wouldn't mind it being 
silent. If we want to debug a potential misdetection, tracing could be 
enabled to track down what's happening.

> Cheers,
>
> Hannes