linux-kernel - Re: [PATCH v17 04/10] fs/ntfs3: Add file operations and implementation

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Message-ID: <20210103220444.GA28414@casper.infradead.org>
Date:   Sun, 3 Jan 2021 22:04:44 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Kari Argillander <kari.argillander@...il.com>
Cc:     Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
        linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
        linux-kernel@...r.kernel.org, pali@...nel.org, dsterba@...e.cz,
        aaptel@...e.com, rdunlap@...radead.org, joe@...ches.com,
        mark@...mstone.com, nborisov@...e.com,
        linux-ntfs-dev@...ts.sourceforge.net, anton@...era.com,
        dan.carpenter@...cle.com, hch@....de, ebiggers@...nel.org,
        andy.lavr@...il.com
Subject: Re: [PATCH v17 04/10] fs/ntfs3: Add file operations and
 implementation

On Sun, Jan 03, 2021 at 11:57:32PM +0200, Kari Argillander wrote:
> > +		/*
> > +		 * mirror of len, but signed, because run_packed_size()
> > +		 * works with signed int only
> > +		 */
> > +		len64 = len;
> > +
> > +		/* how much bytes is packed len64 */
> > +		size_size = run_packed_size(&len64);
> 
> Does (s64 *)&len work just fine?

No.  run_packed_size() is going to load/store eight bytes to/from that
pointer.  You can't just cast a pointer to a different size and expect
it to work (it might happen to work, particularly on little-endian,
but big-endian is going to get completely the wrong value).