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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>
This commit is contained in:
Qu Wenruo 2022-04-20 16:08:28 +08:00 committed by David Sterba
parent f04fbcc64e
commit 719fae8920
2 changed files with 35 additions and 26 deletions
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22
fs/btrfs/volumes.c
View File

@ -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;
const u64 profile = (flags & BTRFS_BLOCK_GROUP_PROFILE_MASK);
return BTRFS_RAID_SINGLE; /* BTRFS_BLOCK_GROUP_SINGLE */
if (!profile)
return BTRFS_RAID_SINGLE;
return BTRFS_BG_FLAG_TO_INDEX(profile);
}
const char *btrfs_bg_type_to_raid_name(u64 flags)

39
fs/btrfs/volumes.h
View File

@ -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
};