linux-kernel - Re: [PATCH v6 07/34] iov_iter: Add a function to extract a page list from an iterator

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Message-ID: <Y8ZV9x9gawJPbQho@infradead.org>
Date:   Tue, 17 Jan 2023 00:01:59 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 07/34] iov_iter: Add a function to extract a page list
 from an iterator

> Changes:
> ========
> ver #6)
>  - Add back the function to indicate the cleanup mode.
>  - Drop the cleanup_mode return arg to iov_iter_extract_pages().
>  - Pass FOLL_SOURCE/DEST_BUF in gup_flags.  Check this against the iter
>    data_source.

FYI, the changelog goes after the --- so that it doesn't get added
to the git history.

> Link: https://lore.kernel.org/r/166732025748.3186319.8314014902727092626.stgit@warthog.procyon.org.uk/ # rfc
> Link: https://lore.kernel.org/r/166869689451.3723671.18242195992447653092.stgit@warthog.procyon.org.uk/ # rfc
> Link: https://lore.kernel.org/r/166920903885.1461876.692029808682876184.stgit@warthog.procyon.org.uk/ # v2
> Link: https://lore.kernel.org/r/166997421646.9475.14837976344157464997.stgit@warthog.procyon.org.uk/ # v3
> Link: https://lore.kernel.org/r/167305163883.1521586.10777155475378874823.stgit@warthog.procyon.org.uk/ # v4
> Link: https://lore.kernel.org/r/167344728530.2425628.9613910866466387722.stgit@warthog.procyon.org.uk/ # v5

And all these links aren't exactly useful.  This fairly trivial commit
is going to look like a hot mess in git.

> +ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages,
> +			       size_t maxsize, unsigned int maxpages,
> +			       unsigned int gup_flags, size_t *offset0);

This function isn't actually added in the current patch.

> +#define iov_iter_extract_mode(iter, gup_flags) \
> +	(user_backed_iter(iter) ?				\
> +	 (gup_flags & FOLL_BUF_MASK) == FOLL_SOURCE_BUF ?	\
> +	 FOLL_GET : FOLL_PIN : 0)

And inline function would be nice here.  I guess that would require
moving the FULL flags into mm_types.h, though.