linux-kernel - Re: [PATCH 1/8] cxl: Add helper function to retrieve a feature entry

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Message-ID: <Z89LcUIWO9m8Vtru@aschofie-mobl2.lan>
Date: Mon, 10 Mar 2025 13:28:33 -0700
From: Alison Schofield <alison.schofield@...el.com>
To: Shiju Jose <shiju.jose@...wei.com>
Cc: "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
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Subject: Re: [PATCH 1/8] cxl: Add helper function to retrieve a feature entry

On Mon, Mar 10, 2025 at 06:15:38PM +0000, Shiju Jose wrote:
> >-----Original Message-----
> >From: Alison Schofield <alison.schofield@...el.com>
> >Sent: 07 March 2025 19:20
> >To: Shiju Jose <shiju.jose@...wei.com>
> [...]
> >> +struct cxl_feat_entry *cxl_get_feature_entry(struct cxl_dev_state *cxlds,
> >> +					     const uuid_t *feat_uuid)
> >> +{
> >> +	struct cxl_features_state *cxlfs = to_cxlfs(cxlds);
> >> +	struct cxl_feat_entry *feat_entry;
> >> +	int count;
> >> +
> >> +	/*
> >> +	 * Retrieve the feature entry from the supported features list,
> >> +	 * if the feature is supported.
> >> +	 */
> >> +	feat_entry = cxlfs->entries->ent;
> >
> >Do we need some NULL checking here on cxlfs, entries
> 
> Hi Alison,
> 
> Thanks for the feedbacks.
> We had check on cxlfs before
> https://lore.kernel.org/all/20250122235159.2716036-5-dave.jiang@intel.com/
> but removed because of the following comment.
> https://lore.kernel.org/all/20250124150150.GZ5556@nvidia.com/

Hi Shiju,

I have not followed all along, so yeah my questions may be a bit pesky
at this point. I did see the comment linked above about how the driver
must be bound at this point. I think my question is a bit different.

Are each of these guaranteed not to be NULL here:

to_cxlfs(cxlds)
cxlfs->entries
cxlfs->entries->ent

If these cannot be NULL, then all good.

--Alison



> >
> >
> >> +	for (count = 0; count < cxlfs->entries->num_features; count++,
> >> +feat_entry++) {
> >
> >Was num_features previously validated?
> Not in the caller. Had check for num_features here before in cxl_get_feature_entry()
> as seen in the above link.
> >
> >> +		if (uuid_equal(&feat_entry->uuid, feat_uuid))
> >> +			return feat_entry;
> >> +	}
> >> +
> >> +	return ERR_PTR(-ENOENT);
> >
> >Why not just return NULL?
> Will do.
> >
> >
> >> +}
> >> +
> >>  size_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
> >>  		       enum cxl_get_feat_selection selection,
> >>  		       void *feat_out, size_t feat_out_size, u16 offset,
> >> --
> >> 2.43.0
> >>
> 
> Thanks,
> Shiju
>