From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A10C9C433F5 for ; Wed, 20 Apr 2022 08:08:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376636AbiDTILi (ORCPT ); Wed, 20 Apr 2022 04:11:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37108 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376560AbiDTILf (ORCPT ); Wed, 20 Apr 2022 04:11:35 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BCD00C16 for ; Wed, 20 Apr 2022 01:08:50 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 5D7751F385 for ; Wed, 20 Apr 2022 08:08:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1650442129; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=vFlfb9VsDbk/wZFU9xeutkXCmD5+fyyS7SG7ed4Gyw8=; b=OGccdQOYAYO/CtKI2C8pEXVum2fkZz9C1KLOY0V0gJoLJLFZb5NsOQB1ufgvtXMAbS3SvR uq7uvF/WWlx7QCjLQCJmowMKADzqYjS102ARBsuvSr6m5wzrcM9ivGXhcZVYmay+FfVNIo rVwz159o9UrkiyIcigy3I9t6p01Ra7Y= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 977A113AD5 for ; Wed, 20 Apr 2022 08:08:48 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id AO0QFpC/X2JEbAAAMHmgww (envelope-from ) for ; Wed, 20 Apr 2022 08:08:48 +0000 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Subject: [PATCH v3 2/2] btrfs: use ilog2() to replace if () branches for btrfs_bg_flags_to_raid_index() Date: Wed, 20 Apr 2022 16:08:28 +0800 Message-Id: X-Mailer: git-send-email 2.35.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org In function btrfs_bg_flags_to_raid_index(), we use quite some if () to convert the BTRFS_BLOCK_GROUP_* bits to a index number. But the truth is, there is really no such need for so many branches at all. Since all BTRFS_BLOCK_GROUP_* flags are just one single bit set inside BTRFS_BLOCK_GROUP_PROFILES_MASK, we can easily use ilog2() to calculate their values. This calculation has an anchor point, the lowest PROFILE bit, which is RAID0. Even it's fixed on-disk format and should never change, here I added extra compile time checks to make it super safe: 1. Make sure RAID0 is always the lowest bit in PROFILE_MASK This is done by finding the first (least significant) bit set of RAID0 and PROFILE_MASK & ~RAID0. 2. Make sure RAID0 bit set beyond the highest bit of TYPE_MASK Signed-off-by: Qu Wenruo --- fs/btrfs/volumes.c | 24 ++++++------------------ fs/btrfs/volumes.h | 40 +++++++++++++++++++++++++++++++--------- 2 files changed, 37 insertions(+), 27 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 2368a2ffbee7..4cfe6daa0fee 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -164,24 +164,12 @@ const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = { */ enum btrfs_raid_types __attribute_const__ btrfs_bg_flags_to_raid_index(u64 flags) { - if (flags & BTRFS_BLOCK_GROUP_RAID10) - return BTRFS_RAID_RAID10; - else if (flags & BTRFS_BLOCK_GROUP_RAID1) - return BTRFS_RAID_RAID1; - else if (flags & BTRFS_BLOCK_GROUP_RAID1C3) - return BTRFS_RAID_RAID1C3; - else if (flags & BTRFS_BLOCK_GROUP_RAID1C4) - return BTRFS_RAID_RAID1C4; - else if (flags & BTRFS_BLOCK_GROUP_DUP) - return BTRFS_RAID_DUP; - else if (flags & BTRFS_BLOCK_GROUP_RAID0) - return BTRFS_RAID_RAID0; - else if (flags & BTRFS_BLOCK_GROUP_RAID5) - return BTRFS_RAID_RAID5; - else if (flags & BTRFS_BLOCK_GROUP_RAID6) - return BTRFS_RAID_RAID6; - - return BTRFS_RAID_SINGLE; /* BTRFS_BLOCK_GROUP_SINGLE */ + u64 profile = flags & BTRFS_BLOCK_GROUP_PROFILE_MASK; + + if (!profile) + return BTRFS_RAID_SINGLE; + + return BTRFS_BG_FLAG_TO_INDEX(profile); } const char *btrfs_bg_type_to_raid_name(u64 flags) diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h index dbb15e4eaa50..627f1ae672c4 100644 --- a/fs/btrfs/volumes.h +++ b/fs/btrfs/volumes.h @@ -17,16 +17,38 @@ extern struct mutex uuid_mutex; #define BTRFS_STRIPE_LEN SZ_64K +/* Used by sanity check for btrfs_raid_types. */ +#define const_ffs(n) (__builtin_ctzll(n) + 1) + +/* + * The conversion from BTRFS_BLOCK_GROUP_* bits to btrfs_raid_type requires + * RAID0 always to be the lowest profile bit. + * Although it's part of on-disk format and should never change, just do extra + * compile time sanity check on it. + */ +static_assert(const_ffs(BTRFS_BLOCK_GROUP_RAID0) < + const_ffs(BTRFS_BLOCK_GROUP_PROFILE_MASK & + ~BTRFS_BLOCK_GROUP_RAID0)); +static_assert(const_ilog2(BTRFS_BLOCK_GROUP_RAID0) > + ilog2(BTRFS_BLOCK_GROUP_TYPE_MASK)); + +/* ilog2() can handle both constants and variables */ +#define BTRFS_BG_FLAG_TO_INDEX(profile) \ + ilog2((profile) >> (ilog2(BTRFS_BLOCK_GROUP_RAID0) - 1)) + enum btrfs_raid_types { - BTRFS_RAID_RAID10, - BTRFS_RAID_RAID1, - BTRFS_RAID_DUP, - BTRFS_RAID_RAID0, - BTRFS_RAID_SINGLE, - BTRFS_RAID_RAID5, - BTRFS_RAID_RAID6, - BTRFS_RAID_RAID1C3, - BTRFS_RAID_RAID1C4, + /* SINGLE is the special one as it doesn't have on-disk bit. */ + BTRFS_RAID_SINGLE = 0, + + BTRFS_RAID_RAID0 = BTRFS_BG_FLAG_TO_INDEX(BTRFS_BLOCK_GROUP_RAID0), + BTRFS_RAID_RAID1 = BTRFS_BG_FLAG_TO_INDEX(BTRFS_BLOCK_GROUP_RAID1), + BTRFS_RAID_DUP = BTRFS_BG_FLAG_TO_INDEX(BTRFS_BLOCK_GROUP_DUP), + BTRFS_RAID_RAID10 = BTRFS_BG_FLAG_TO_INDEX(BTRFS_BLOCK_GROUP_RAID10), + BTRFS_RAID_RAID5 = BTRFS_BG_FLAG_TO_INDEX(BTRFS_BLOCK_GROUP_RAID5), + BTRFS_RAID_RAID6 = BTRFS_BG_FLAG_TO_INDEX(BTRFS_BLOCK_GROUP_RAID6), + BTRFS_RAID_RAID1C3 = BTRFS_BG_FLAG_TO_INDEX(BTRFS_BLOCK_GROUP_RAID1C3), + BTRFS_RAID_RAID1C4 = BTRFS_BG_FLAG_TO_INDEX(BTRFS_BLOCK_GROUP_RAID1C4), + BTRFS_NR_RAID_TYPES }; -- 2.35.1