linux-kernel - Re: [PATCH v10 2/8] iov_iter: Add a function to extract a page list from an iterator

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Message-ID: <2642250.1674733015@warthog.procyon.org.uk>
Date:   Thu, 26 Jan 2023 11:36:55 +0000
From:   David Howells <dhowells@...hat.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     dhowells@...hat.com, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v10 2/8] iov_iter: Add a function to extract a page list from an iterator

iov_iter_extract_kvec_pages() isn't quite right.  The problem is that there's
not currently any path by which it can be tested, as currently
iov_iter_get_pages*() balk at it, but I managed to do that by piggybacking
some testing code on my cifs patches.

The attached change fixes the problem.

David

--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -2080,9 +2080,9 @@ static ssize_t iov_iter_extract_kvec_pages(struct iov_iter *i,
 		skip = 0;
 	}
 
-	offset = skip % PAGE_SIZE;
+	kaddr = i->kvec->iov_base + skip;
+	offset = (unsigned long)kaddr & ~PAGE_MASK;
 	*offset0 = offset;
-	kaddr = i->kvec->iov_base;
 
 	maxpages = want_pages_array(pages, maxsize, offset, maxpages);
 	if (!maxpages)