linux-kernel - RE: [PATCH 01/29] iov_iter: Switch to using a table of operations

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Message-ID: <4cf03398b2bb47e28d13fae4b62185f5@AcuMS.aculab.com>
Date:   Sun, 22 Nov 2020 22:46:51 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'David Howells' <dhowells@...hat.com>,
        Pavel Begunkov <asml.silence@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 01/29] iov_iter: Switch to using a table of operations

From: David Howells
> Sent: 21 November 2020 14:14
> 
> Switch to using a table of operations.  In a future patch the individual
> methods will be split up by type.  For the moment, however, the ops tables
> just jump directly to the old functions - which are now static.  Inline
> wrappers are provided to jump through the hooks.

I was wondering if you could use a bit of 'cpp magic'
so the to call sites would be:
	ITER_CALL(iter, action)(arg_list);

which might expand to:
	iter->action(arg_list);
in the function-table case.
But could also be an if-chain:
	if (iter->type & foo)
		foo_action(args);
	else ...
with foo_action() being inlined.

If there is enough symmetry it might make the code easier to read.
Although I'm not sure what happens to 'iterate_all_kinds'.
OTOH that is already unreadable.

	David

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