From 719fae8920e4f42643ea306b95addb40bec87a25 Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@suse.com>
Date: Wed, 20 Apr 2022 16:08:28 +0800
Subject: btrfs: use ilog2() to replace if () branches for
btrfs_bg_flags_to_raid_index()
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 <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/volumes.h | 39 ++++++++++++++++++++++++++++++---------
1 file changed, 30 insertions(+), 9 deletions(-)
(limited to 'fs/btrfs/volumes.h')
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 7b82aae89454..12b2af9260e9 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -17,16 +17,37 @@ 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, do extra
+ * compile-time sanity checks.
+ */
+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
};
--
cgit