Commit 719fae89 authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

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: default avatarQu Wenruo <wqu@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent f04fbcc6

fs/btrfs/volumes.c

+6 −18
Original line number Diff line number Diff line
@@ -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 */

	const 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)

fs/btrfs/volumes.h

+30 −9
Original line number Diff line number Diff line
@@ -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

};