Btrfs: add BTRFS_AVAIL_ALLOC_BIT_SINGLE bit

Right now on-disk BTRFS_BLOCK_GROUP_* profile bits are used for
avail_{data,metadata,system}_alloc_bits fields, which gather info about
available allocation profiles in the FS.  When chunk is created or read
from disk, its profile is OR'ed with the corresponding avail_alloc_bits
field.  Since SINGLE is denoted by 0 in the on-disk format, currently
there is no way to tell when such chunks become avaialble.  Restriper
needs that information, so add a separate bit for SINGLE profile.

This bit is going to be in-memory only, it should never be written out
to disk, so it's not a disk format change.  However to avoid remappings
in future, reserve corresponding on-disk bit.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

2 files changed, 36 insertions, 9 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 4370a56fe81a..3f8f11e18b53 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -758,6 +758,7 @@ struct btrfs_csum_item {
 #define BTRFS_BLOCK_GROUP_RAID1         (1ULL << 4)
 #define BTRFS_BLOCK_GROUP_DUP           (1ULL << 5)
 #define BTRFS_BLOCK_GROUP_RAID10        (1ULL << 6)
+#define BTRFS_BLOCK_GROUP_RESERVED      BTRFS_AVAIL_ALLOC_BIT_SINGLE
 #define BTRFS_NR_RAID_TYPES             5
 
 #define BTRFS_BLOCK_GROUP_TYPE_MASK     (BTRFS_BLOCK_GROUP_DATA |    \
@@ -768,6 +769,15 @@ struct btrfs_csum_item {
                                          BTRFS_BLOCK_GROUP_RAID1 |   \
                                          BTRFS_BLOCK_GROUP_DUP |     \
                                          BTRFS_BLOCK_GROUP_RAID10)
+/*
+ * We need a bit for restriper to be able to tell when chunks of type
+ * SINGLE are available.  This "extended" profile format is used in
+ * fs_info->avail_*_alloc_bits (in-memory) and balance item fields
+ * (on-disk).  The corresponding on-disk bit in chunk.type is reserved
+ * to avoid remappings between two formats in future.
+ */
+#define BTRFS_AVAIL_ALLOC_BIT_SINGLE    (1ULL << 48)
+
 struct btrfs_block_group_item {
         __le64 used;
         __le64 chunk_objectid;
@@ -1140,6 +1150,11 @@ struct btrfs_fs_info {
         spinlock_t ref_cache_lock;
         u64 total_ref_cache_size;
 
+        /*
+         * these three are in extended format (availability of single
+         * chunks is denoted by BTRFS_AVAIL_ALLOC_BIT_SINGLE bit, other
+         * types are denoted by corresponding BTRFS_BLOCK_GROUP_* bits)
+         */
         u64 avail_data_alloc_bits;
         u64 avail_metadata_alloc_bits;
         u64 avail_system_alloc_bits;
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a8d8204188d1..15a22949da17 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3014,16 +3014,24 @@ static int update_space_info(struct btrfs_fs_info *info, u64 flags,
 static void set_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
 {
         u64 extra_flags = flags & BTRFS_BLOCK_GROUP_PROFILE_MASK;
-        if (extra_flags) {
-                if (flags & BTRFS_BLOCK_GROUP_DATA)
-                        fs_info->avail_data_alloc_bits |= extra_flags;
-                if (flags & BTRFS_BLOCK_GROUP_METADATA)
-                        fs_info->avail_metadata_alloc_bits |= extra_flags;
-                if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
-                        fs_info->avail_system_alloc_bits |= extra_flags;
-        }
+
+        /* chunk -> extended profile */
+        if (extra_flags == 0)
+                extra_flags = BTRFS_AVAIL_ALLOC_BIT_SINGLE;
+
+        if (flags & BTRFS_BLOCK_GROUP_DATA)
+                fs_info->avail_data_alloc_bits |= extra_flags;
+        if (flags & BTRFS_BLOCK_GROUP_METADATA)
+                fs_info->avail_metadata_alloc_bits |= extra_flags;
+        if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
+                fs_info->avail_system_alloc_bits |= extra_flags;
 }
 
+/*
+ * @flags: available profiles in extended format (see ctree.h)
+ *
+ * Returns reduced profile in chunk format.
+ */
 u64 btrfs_reduce_alloc_profile(struct btrfs_root *root, u64 flags)
 {
         /*
@@ -3053,8 +3061,12 @@ u64 btrfs_reduce_alloc_profile(struct btrfs_root *root, u64 flags)
         if ((flags & BTRFS_BLOCK_GROUP_RAID0) &&
             ((flags & BTRFS_BLOCK_GROUP_RAID1) |
              (flags & BTRFS_BLOCK_GROUP_RAID10) |
-             (flags & BTRFS_BLOCK_GROUP_DUP)))
+             (flags & BTRFS_BLOCK_GROUP_DUP))) {
                 flags &= ~BTRFS_BLOCK_GROUP_RAID0;
+        }
+
+        /* extended -> chunk profile */
+        flags &= ~BTRFS_AVAIL_ALLOC_BIT_SINGLE;
         return flags;
 }