From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A68DA1C280 for ; Wed, 3 Apr 2024 03:57:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712116648; cv=none; b=se53EM4RjttIgtp6we70PEpeGnsW8tlWxDFb/ETTBMubEIW9MKSy0nZ052YA++DTX8fEOTbTCbPijmw02pfhDKjTQ8iqeWBkd17h49mWqOSRM+1L/UHuFqKJGbyLh6bDzTLg4VPhGjvFgmc+OAnvSRo1vNKk56uVlBbVuFEFdDw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712116648; c=relaxed/simple; bh=Jr1baXMrY541pl+WZ6KbZu2FigJKzTtCqt8w4Zs65W0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HQVTc3FwK1BTufDDV3A9Am2J+YXdL/uEe66jBJ7eXF8FNC21JDoGxj/mJUBS5/ZEVr6PcgoPNsJ4C01E4wSsJXel1GR7lMr51IREScs+K37WW3Uh/pNozX/CE0DjG1k30kdTj/IyLbGX0BxqJf8CjA3NdYuBF5dU5AoFwXzkqFY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hwun5vic; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hwun5vic" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3B5BDC433C7; Wed, 3 Apr 2024 03:57:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1712116648; bh=Jr1baXMrY541pl+WZ6KbZu2FigJKzTtCqt8w4Zs65W0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hwun5vicnalX40OL2EPlG544/ctsCkyWe3M82zilZ3MlaXuGHgVyXR3kV6pL3wodX n/JOsxsnn4V7WupwFA891Z8Dgav3PqNqt1t5xqwe30KebTaC+7anPNtw3qGGZ0X7Qx PbRfKJHrQwVkDWlIg5KGu9oN47fkZ8MlRUzS+8igL4IAU6pDDhbcNfj2mO241y+PVg mZM0ZtUNsNNBe4q63pnJ5fw/KLWYD3KpslHlc5UzHyjhRKyc8VZjFIcOHx/iYMO41G XXHtXwgJudKCYrWB3wfeOsPpqDX35dlkDLL4NhoQrZRdVOC/vWGlM9IKzHlnsBO7XK JrZDXgVVVky7g== Date: Tue, 2 Apr 2024 20:57:27 -0700 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 3/5] xfs: silence sparse warning when checking version number Message-ID: <20240403035727.GO6390@frogsfrogsfrogs> References: <20240402213541.1199959-1-david@fromorbit.com> <20240402213541.1199959-4-david@fromorbit.com> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240402213541.1199959-4-david@fromorbit.com> On Wed, Apr 03, 2024 at 08:28:30AM +1100, Dave Chinner wrote: > From: Dave Chinner > > Scrub checks the superblock version number against the known good > feature bits that can be set in the version mask. It calculates > the version mask to compare like so: > > vernum_mask = cpu_to_be16(~XFS_SB_VERSION_OKBITS | > XFS_SB_VERSION_NUMBITS | > XFS_SB_VERSION_ALIGNBIT | > XFS_SB_VERSION_DALIGNBIT | > XFS_SB_VERSION_SHAREDBIT | > XFS_SB_VERSION_LOGV2BIT | > XFS_SB_VERSION_SECTORBIT | > XFS_SB_VERSION_EXTFLGBIT | > XFS_SB_VERSION_DIRV2BIT); > > This generates a sparse warning: > > fs/xfs/scrub/agheader.c:168:23: warning: cast truncates bits from constant value (ffff3f8f becomes 3f8f) > > This is because '~XFS_SB_VERSION_OKBITS' is considered a 32 bit > constant, even though it's value is always under 16 bits. > > This is a kinda silly thing to do, because: > > /* > * Supported feature bit list is just all bits in the versionnum field because > * we've used them all up and understand them all. Except, of course, for the > * shared superblock bit, which nobody knows what it does and so is unsupported. > */ > #define XFS_SB_VERSION_OKBITS \ > ((XFS_SB_VERSION_NUMBITS | XFS_SB_VERSION_ALLFBITS) & \ > ~XFS_SB_VERSION_SHAREDBIT) > > #define XFS_SB_VERSION_NUMBITS 0x000f > #define XFS_SB_VERSION_ALLFBITS 0xfff0 > #define XFS_SB_VERSION_SHAREDBIT 0x0200 > > > XFS_SB_VERSION_OKBITS has a value of 0xfdff, and so > ~XFS_SB_VERSION_OKBITS == XFS_SB_VERSION_SHAREDBIT. The calculated > mask already sets XFS_SB_VERSION_SHAREDBIT, so starting with > ~XFS_SB_VERSION_OKBITS is completely redundant.... > > Signed-off-by: Dave Chinner What a tongue twister! Reviewed-by: Darrick J. Wong --D > --- > fs/xfs/scrub/agheader.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/fs/xfs/scrub/agheader.c b/fs/xfs/scrub/agheader.c > index e954f07679dd..d6a1a9fc63c9 100644 > --- a/fs/xfs/scrub/agheader.c > +++ b/fs/xfs/scrub/agheader.c > @@ -165,8 +165,7 @@ xchk_superblock( > xchk_block_set_corrupt(sc, bp); > > /* Check sb_versionnum bits that are set at mkfs time. */ > - vernum_mask = cpu_to_be16(~XFS_SB_VERSION_OKBITS | > - XFS_SB_VERSION_NUMBITS | > + vernum_mask = cpu_to_be16(XFS_SB_VERSION_NUMBITS | > XFS_SB_VERSION_ALIGNBIT | > XFS_SB_VERSION_DALIGNBIT | > XFS_SB_VERSION_SHAREDBIT | > -- > 2.43.0 > >