From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (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 6A7BC5CB8 for ; Thu, 10 Apr 2025 00:02:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744243336; cv=none; b=X9zHgrnUI3fyk0n4rcsjgMfDEnlaeoq3Asj9IM0evTBKF4cu4IHLKxuD05ZeMWtvsMFaK5LkV3qZLJyv2Fr/IbWXB/e24udsFkHfD8vw5XH7z4Y4LAZSjkQlK9PY5ZZyi7feDCHL1iEiAjvc/XQW6gdR2gNCvj7vVKUyHtXjStY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744243336; c=relaxed/simple; bh=rKF1hbfcgw75F2EN5uNgusCOV3BqZbHH4JOjXRGX65w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dgbUN4cqtW44i0OxtpWnAau/ste+Lcf21+BZGvH+X7AVR6HhpZGnBMbyk52FkKo5pRBehqgfW9A4lZz61cum+Dybvobq/zuTAC37TnVu1r/621HbPKT9/vZ2sl1IqwKacpIKU2sD4ovE1WIVwx76BGr9PiILJ9AhvI1iSygCtmU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=CErOvc4u; arc=none smtp.client-ip=115.124.30.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="CErOvc4u" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1744243324; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=Aoq6JYCaV1p9yraciQnzm7D38594vGRZlTcVPXdUJs8=; b=CErOvc4ukleVfOY+MFBpeEjrFbzWoD0cZXlHnn1TBPkJrRceYDh9pfwcj/LS7KpXkTzdGHSsPgu2I6AWlpoQMWu5+0ryWGeCboWJ6T9LiphyAEtGnEUKBdDjTxJ2FO9IKSSmyhvzsGGlZVDgHPLjq7j0WLMyaaIif/tBgwHd4E0= Received: from 30.134.5.237(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0WWLx0T9_1744243006 cluster:ay36) by smtp.aliyun-inc.com; Thu, 10 Apr 2025 07:56:46 +0800 Message-ID: <7af3e868-04cb-47b1-a81b-651be3756ec5@linux.alibaba.com> Date: Thu, 10 Apr 2025 07:56:45 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] erofs: add __packed annotation to union(__le16..) To: David Laight Cc: linux-erofs@lists.ozlabs.org, LKML , kernel test robot References: <20250408114448.4040220-1-hsiangkao@linux.alibaba.com> <20250409195222.4cadc368@pumpkin> From: Gao Xiang In-Reply-To: <20250409195222.4cadc368@pumpkin> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi David, On 2025/4/10 02:52, David Laight wrote: > On Tue, 8 Apr 2025 19:44:47 +0800 > Gao Xiang wrote: > >> I'm unsure why they aren't 2 bytes in size only in arm-linux-gnueabi. > > IIRC one of the arm ABI aligns structures on 32 bit boundaries. Thanks for your reply, but I'm not sure if it's the issue. > >> >> Reported-by: kernel test robot >> Closes: https://lore.kernel.org/r/202504051202.DS7QIknJ-lkp@intel.com >> Fixes: 61ba89b57905 ("erofs: add 48-bit block addressing on-disk support") >> Fixes: efb2aef569b3 ("erofs: add encoded extent on-disk definition") >> Signed-off-by: Gao Xiang >> --- >> fs/erofs/erofs_fs.h | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> >> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h >> index 61a5ee11f187..94bf636776b0 100644 >> --- a/fs/erofs/erofs_fs.h >> +++ b/fs/erofs/erofs_fs.h >> @@ -56,7 +56,7 @@ struct erofs_super_block { >> union { >> __le16 rootnid_2b; /* nid of root directory */ >> __le16 blocks_hi; /* (48BIT on) blocks count MSB */ >> - } rb; >> + } __packed rb; >> __le64 inos; /* total valid ino # (== f_files - f_favail) */ >> __le64 epoch; /* base seconds used for compact inodes */ >> __le32 fixed_nsec; /* fixed nanoseconds for compact inodes */ >> @@ -148,7 +148,7 @@ union erofs_inode_i_nb { >> __le16 nlink; /* if EROFS_I_NLINK_1_BIT is unset */ >> __le16 blocks_hi; /* total blocks count MSB */ >> __le16 startblk_hi; /* starting block number MSB */ >> -}; >> +} __packed; > > That shouldn't be necessary and will kill performance on some systems. > The 'packed' on the member should be enough to reduce the size. It cannot be resolved by the following diff: diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h index 94bf636776b0..1f6233dfdcb0 100644 --- a/fs/erofs/erofs_fs.h +++ b/fs/erofs/erofs_fs.h @@ -148,14 +148,14 @@ union erofs_inode_i_nb { __le16 nlink; /* if EROFS_I_NLINK_1_BIT is unset */ __le16 blocks_hi; /* total blocks count MSB */ __le16 startblk_hi; /* starting block number MSB */ -} __packed; +}; /* 32-byte reduced form of an ondisk inode */ struct erofs_inode_compact { __le16 i_format; /* inode format hints */ __le16 i_xattr_icount; __le16 i_mode; - union erofs_inode_i_nb i_nb; + union erofs_inode_i_nb i_nb __packed; __le32 i_size; __le32 i_mtime; union erofs_inode_i_u i_u; @@ -171,7 +171,7 @@ struct erofs_inode_extended { __le16 i_format; /* inode format hints */ __le16 i_xattr_icount; __le16 i_mode; - union erofs_inode_i_nb i_nb; + union erofs_inode_i_nb i_nb __packed; __le64 i_size; union erofs_inode_i_u i_u; I doesn't work and will report In file included from : In function 'erofs_check_ondisk_layout_definitions', inlined from 'erofs_module_init' at ../fs/erofs/super.c:817:2: ./../include/linux/compiler_types.h:542:38: error: call to '__compiletime_assert_332' declared with attribute error: BUILD_BUG_ON failed: sizeof(struct erofs_inode_compact) != 32 542 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | > > I'd add a compile assert (of some form) on the size of the structure. you mean @@ -435,6 +435,7 @@ static inline void erofs_check_ondisk_layout_definitions(void) }; BUILD_BUG_ON(sizeof(struct erofs_super_block) != 128); + BUILD_BUG_ON(sizeof(union erofs_inode_i_nb) != 2); BUILD_BUG_ON(sizeof(struct erofs_inode_compact) != 32); ? ./../include/linux/compiler_types.h:542:38: error: call to '__compiletime_assert_332' declared with attribute error: BUILD_BUG_ON failed: sizeof(union erofs_inode_i_nb) != 2 542 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^ That doesn't work too. Thanks, Gao Xiang