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Message-ID: <4032545.1692018789@warthog.procyon.org.uk>
Date: Mon, 14 Aug 2023 14:13:09 +0100
From: David Howells <dhowells@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: dhowells@...hat.com, Alexander Viro <viro@...iv.linux.org.uk>,
Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
Christian Brauner <christian@...uner.io>,
Matthew Wilcox <willy@...radead.org>, jlayton@...nel.org,
linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] iov_iter: Convert iterate*() to inline funcs
Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
> So I think you need to remove the changes you did to
> memcpy_from_iter(). The old code was an explicit conditional of direct
> calls:
>
> if (iov_iter_is_copy_mc(i))
> return (void *)copy_mc_to_kernel(to, from, size);
> return memcpy(to, from, size);
>
> and now you do that
>
> iov_iter_is_copy_mc(i) ?
> memcpy_from_iter_mc : memcpy_from_iter);
>
> to pass in a function pointer.
>
> Not ok. Not ok at all. It may look clever, but function pointers are
> bad. Avoid them like the plague.
Yeah. I was hoping that the compiler would manage to inline that, but it just
does an indirect call. I'm trying to avoid passing the iterator as that makes
things bigger. I think I can probably share the extra argument used for
passing checksums.
David
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