linux-kernel - Re: [PATCH 3/4] block: add IOC_PR_READ

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Message-ID: <20251201183621.GA919572@fedora>
Date: Mon, 1 Dec 2025 13:36:21 -0500
From: Stefan Hajnoczi <stefanha@...hat.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Hannes Reinecke <hare@...e.de>, linux-block@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-kernel@...r.kernel.org,
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
	Mike Christie <michael.christie@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, linux-nvme@...ts.infradead.org,
	Keith Busch <kbusch@...nel.org>, Sagi Grimberg <sagi@...mberg.me>,
	linux-scsi@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 3/4] block: add IOC_PR_READ_KEYS ioctl

On Mon, Dec 01, 2025 at 05:26:27PM +0100, Krzysztof Kozlowski wrote:
> On 01/12/2025 16:06, Stefan Hajnoczi wrote:
> > On Sat, Nov 29, 2025 at 03:32:35PM +0100, Krzysztof Kozlowski wrote:
> >> On 27/11/2025 08:07, Hannes Reinecke wrote:
> >>>
> >>>> +	size_t keys_info_len = struct_size(keys_info, keys, inout.num_keys);
> >>>> +
> >>>> +	keys_info = kzalloc(keys_info_len, GFP_KERNEL);
> >>>> +	if (!keys_info)
> >>>> +		return -ENOMEM;
> >>>> +
> >>>> +	keys_info->num_keys = inout.num_keys;
> >>>> +
> >>>> +	ret = ops->pr_read_keys(bdev, keys_info);
> >>>> +	if (ret)
> >>>> +		return ret;
> >>>> +
> >>>> +	/* Copy out individual keys */
> >>>> +	u64 __user *keys_ptr = u64_to_user_ptr(inout.keys_ptr);
> >>>> +	u32 num_copy_keys = min(inout.num_keys, keys_info->num_keys);
> >>>> +	size_t keys_copy_len = num_copy_keys * sizeof(keys_info->keys[0]);
> >>>
> >>> We just had the discussion about variable declarations on the ksummit 
> >>> lists; I really would prefer to have all declarations at the start of 
> >>> the scope (read: at the start of the function here).
> >>
> >> Then also cleanup.h should not be used here.
> > 
> > Hi Krzysztof,
> > The documentation in cleanup.h says:
> > 
> >  * Given that the "__free(...) = NULL" pattern for variables defined at
> >  * the top of the function poses this potential interdependency problem
> >  * the recommendation is to always define and assign variables in one
> >        ^^^^^^^^^^^^^^
> >  * statement and not group variable definitions at the top of the
> >  * function when __free() is used.
> > 
> > This is a recommendation, not mandatory. It is also describing a
> > scenario that does not apply here.
> 
> If you have actual argument, so allocation in some if branch, the of course.

I'm pointing out that the documentation uses the word "recommendation",
which is usually not considered mandatory but a suggestion.

Please update the documentation to clarify that __free() _must_ be
assigned the real value (no NULL initialization) so that it's clear this
is not a suggestion but mandatory.

Stefan

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