linux-kernel - Re: [PATCH v2 2/4] block: add private field to struct keyslot

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Message-ID: <20201016071941.GA14885@infradead.org>
Date:   Fri, 16 Oct 2020 08:19:41 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Satya Tangirala <satyat@...gle.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        dm-devel@...hat.com, Jens Axboe <axboe@...nel.dk>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH v2 2/4] block: add private field to struct keyslot_manager

On Thu, Oct 15, 2020 at 09:46:30PM +0000, Satya Tangirala wrote:
> Add a (void *) pointer to struct keyslot_manager that the owner of the
> struct can use for any purpose it wants.
> 
> Right now, the struct keyslot_manager is expected to be embedded directly
> into other structs (and the owner of the keyslot_manager would use
> container_of() to access any other data the owner needs). However, this
> might take up more space than is acceptable, and it would be better to be
> able to add only a pointer to a struct keyslot_manager into other structs
> rather than embed the entire struct directly. But container_of() can't be
> used when only the pointer to the keyslot_manager is embded. The primary
> motivation of this patch is to get around that issue.

No, please don't bloat the structure.  If some weird caller doesn't
like the embedding it can create a container structure with the
blk_keyslot_manager structure and a backpointer.