@@ -1,6 +1,6 @@
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
-#ifndef _BTRFS_CTREE_H_
-#define _BTRFS_CTREE_H_
+#ifndef __BTRFS_TREE_H__
+#define __BTRFS_TREE_H__
#include <linux/types.h>
@@ -23,95 +23,98 @@
#define BTRFS_NAME_LEN 255
/*
- * This header contains the structure definitions and constants used
- * by file system objects that can be retrieved using
- * the BTRFS_IOC_SEARCH_TREE ioctl. That means basically anything that
- * is needed to describe a leaf node's key or item contents.
+ * Objectids start from here.
+ *
+ * Check btrfs_disk_key for the meaning of objectids.
*/
-/* holds pointers to all of the tree roots */
+/*
+ * Root tree holds pointers to all of the tree roots.
+ * Without special mention, the root tree contains the root bytenr of all other
+ * trees, except the chunk tree and the log tree.
+ *
+ * The super block contains the root bytenr of this tree.
+ */
#define BTRFS_ROOT_TREE_OBJECTID 1ULL
-/* stores information about which extents are in use, and reference counts */
+/*
+ * Extent tree stores information about which extents are in use, and backrefs
+ * for each extent.
+ */
#define BTRFS_EXTENT_TREE_OBJECTID 2ULL
/*
- * chunk tree stores translations from logical -> physical block numbering
- * the super block points to the chunk tree
+ * Chunk tree stores btrfs logical address -> physical address mapping.
+ *
+ * The super block contains part of chunk tree for bootstrap, and contains
+ * the root bytenr of this tree.
*/
#define BTRFS_CHUNK_TREE_OBJECTID 3ULL
/*
- * stores information about which areas of a given device are in use.
- * one per device. The tree of tree roots points to the device tree
+ * Device tree stores info about which areas of a given device are in use,
+ * and physical address -> btrfs logical address mapping.
*/
#define BTRFS_DEV_TREE_OBJECTID 4ULL
-/* one per subvolume, storing files and directories */
+/* The fs tree is the first subvolume tree, storing files and directories. */
#define BTRFS_FS_TREE_OBJECTID 5ULL
-/* directory objectid inside the root tree */
+/* Shows the directory objectid inside the root tree. */
#define BTRFS_ROOT_TREE_DIR_OBJECTID 6ULL
-/* holds checksums of all the data extents */
+/* Csum tree holds checksums of all the data extents. */
#define BTRFS_CSUM_TREE_OBJECTID 7ULL
-/* holds quota configuration and tracking */
+/* Quota tree holds quota configuration and tracking. */
#define BTRFS_QUOTA_TREE_OBJECTID 8ULL
-/* for storing items that use the BTRFS_UUID_KEY* types */
+/* UUID tree stores items that use the BTRFS_UUID_KEY* types. */
#define BTRFS_UUID_TREE_OBJECTID 9ULL
-/* tracks free space in block groups. */
+/* Free space cache tree (v2 space cache) tracks free space in block groups. */
#define BTRFS_FREE_SPACE_TREE_OBJECTID 10ULL
-/* device stats in the device tree */
+/* Indicates device stats in the device tree. */
#define BTRFS_DEV_STATS_OBJECTID 0ULL
-/* for storing balance parameters in the root tree */
+/* For storing balance parameters in the root tree. */
#define BTRFS_BALANCE_OBJECTID -4ULL
-/* orhpan objectid for tracking unlinked/truncated files */
+/* Orhpan objectid for tracking unlinked/truncated files. */
#define BTRFS_ORPHAN_OBJECTID -5ULL
-/* does write ahead logging to speed up fsyncs */
+/* Does write ahead logging to speed up fsyncs. */
#define BTRFS_TREE_LOG_OBJECTID -6ULL
#define BTRFS_TREE_LOG_FIXUP_OBJECTID -7ULL
-/* for space balancing */
+/* For space balancing. */
#define BTRFS_TREE_RELOC_OBJECTID -8ULL
#define BTRFS_DATA_RELOC_TREE_OBJECTID -9ULL
-/*
- * extent checksums all have this objectid
- * this allows them to share the logging tree
- * for fsyncs
- */
+/* Extent checksums, shared between the csum tree and log trees. */
#define BTRFS_EXTENT_CSUM_OBJECTID -10ULL
-/* For storing free space cache */
+/* For storing free space cache (v1 space cache). */
#define BTRFS_FREE_SPACE_OBJECTID -11ULL
-/*
- * The inode number assigned to the special inode for storing
- * free ino cache
- */
+/* The inode number assigned to the special inode for storing free ino cache. */
#define BTRFS_FREE_INO_OBJECTID -12ULL
-/* dummy objectid represents multiple objectids */
+/* Dummy objectid represents multiple objectids. */
#define BTRFS_MULTIPLE_OBJECTIDS -255ULL
-/*
- * All files have objectids in this range.
- */
+/* All files have objectids in this range. */
#define BTRFS_FIRST_FREE_OBJECTID 256ULL
#define BTRFS_LAST_FREE_OBJECTID -256ULL
#define BTRFS_FIRST_CHUNK_TREE_OBJECTID 256ULL
/*
- * the device items go into the chunk tree. The key is in the form
- * [ 1 BTRFS_DEV_ITEM_KEY device_id ]
+ * The device items go into the chunk tree.
+ *
+ * The key is in the form
+ * (BTRFS_DEV_ITEMS_OBJECTID, BTRFS_DEV_ITEM_KEY, <device_id>)
*/
#define BTRFS_DEV_ITEMS_OBJECTID 1ULL
@@ -122,58 +125,68 @@
#define BTRFS_DEV_REPLACE_DEVID 0ULL
/*
- * inode items have the data typically returned from stat and store other
- * info about object characteristics. There is one for every file and dir in
- * the FS
+ * Types start from here.
+ *
+ * Check btrfs_disk_key for details about types.
+ */
+
+/*
+ * Inode items have the data typically returned from stat and store other
+ * info about object characteristics.
+ *
+ * There is one for every file and dir in the FS.
*/
#define BTRFS_INODE_ITEM_KEY 1
+/* reserve 2-11 close to the inode for later flexibility */
#define BTRFS_INODE_REF_KEY 12
#define BTRFS_INODE_EXTREF_KEY 13
#define BTRFS_XATTR_ITEM_KEY 24
#define BTRFS_ORPHAN_ITEM_KEY 48
-/* reserve 2-15 close to the inode for later flexibility */
/*
- * dir items are the name -> inode pointers in a directory. There is one
- * for every name in a directory.
+ * Dir items are the name -> inode pointers in a directory.
+ *
+ * There is one for every name in a directory.
*/
#define BTRFS_DIR_LOG_ITEM_KEY 60
#define BTRFS_DIR_LOG_INDEX_KEY 72
#define BTRFS_DIR_ITEM_KEY 84
#define BTRFS_DIR_INDEX_KEY 96
-/*
- * extent data is for file data
- */
+
+/* Stores info (position, size ...) about a data extent of a file */
#define BTRFS_EXTENT_DATA_KEY 108
/*
- * extent csums are stored in a separate tree and hold csums for
+ * Extent csums are stored in a separate tree and hold csums for
* an entire extent on disk.
*/
#define BTRFS_EXTENT_CSUM_KEY 128
/*
- * root items point to tree roots. They are typically in the root
- * tree used by the super block to find all the other trees
+ * Root items point to tree roots.
+ *
+ * They are typically in the root tree used by the super block to find all the
+ * other trees.
*/
#define BTRFS_ROOT_ITEM_KEY 132
/*
- * root backrefs tie subvols and snapshots to the directory entries that
- * reference them
+ * Root backrefs tie subvols and snapshots to the directory entries that
+ * reference them.
*/
#define BTRFS_ROOT_BACKREF_KEY 144
/*
- * root refs make a fast index for listing all of the snapshots and
+ * Root refs make a fast index for listing all of the snapshots and
* subvolumes referenced by a given root. They point directly to the
- * directory item in the root that references the subvol
+ * directory item in the root that references the subvol.
*/
#define BTRFS_ROOT_REF_KEY 156
/*
- * extent items are in the extent map tree. These record which blocks
- * are used, and how many references there are to each block
+ * Extent items are in the extent tree.
+ *
+ * These record which blocks are used, and how many references there are.
*/
#define BTRFS_EXTENT_ITEM_KEY 168
@@ -194,8 +207,9 @@
#define BTRFS_SHARED_DATA_REF_KEY 184
/*
- * block groups give us hints into the extent allocation trees. Which
- * blocks are free etc etc
+ * Block groups give us hints into the extent allocation trees.
+ *
+ * Stores how many free space there is in a block group.
*/
#define BTRFS_BLOCK_GROUP_ITEM_KEY 192
@@ -214,9 +228,10 @@
/*
* When a block group becomes very fragmented, we convert it to use bitmaps
- * instead of extents. A free space bitmap is keyed on
- * (start, FREE_SPACE_BITMAP, length); the corresponding item is a bitmap with
- * (length / sectorsize) bits.
+ * instead of extents.
+ *
+ * A free space bitmap is keyed on (start, FREE_SPACE_BITMAP, length).
+ * The corresponding item is a bitmap with (length / sectorsize) bits.
*/
#define BTRFS_FREE_SPACE_BITMAP_KEY 200
@@ -226,20 +241,25 @@
/*
* Records the overall state of the qgroups.
+ *
* There's only one instance of this key present,
* (0, BTRFS_QGROUP_STATUS_KEY, 0)
*/
#define BTRFS_QGROUP_STATUS_KEY 240
/*
* Records the currently used space of the qgroup.
+ *
* One key per qgroup, (0, BTRFS_QGROUP_INFO_KEY, qgroupid).
*/
#define BTRFS_QGROUP_INFO_KEY 242
+
/*
* Contains the user configured limits for the qgroup.
+ *
* One key per qgroup, (0, BTRFS_QGROUP_LIMIT_KEY, qgroupid).
*/
#define BTRFS_QGROUP_LIMIT_KEY 244
+
/*
* Records the child-parent relationship of qgroups. For
* each relation, 2 keys are present:
@@ -248,9 +268,7 @@
*/
#define BTRFS_QGROUP_RELATION_KEY 246
-/*
- * Obsolete name, see BTRFS_TEMPORARY_ITEM_KEY.
- */
+/* Obsolete name, see BTRFS_TEMPORARY_ITEM_KEY. */
#define BTRFS_BALANCE_ITEM_KEY 248
/*
@@ -266,9 +284,7 @@
*/
#define BTRFS_TEMPORARY_ITEM_KEY 248
-/*
- * Obsolete name, see BTRFS_PERSISTENT_ITEM_KEY
- */
+/* Obsolete name, see BTRFS_PERSISTENT_ITEM_KEY */
#define BTRFS_DEV_STATS_KEY 249
/*
@@ -287,13 +303,15 @@
#define BTRFS_PERSISTENT_ITEM_KEY 249
/*
- * Persistantly stores the device replace state in the device tree.
+ * Persistently stores the device replace state in the device tree.
+ *
* The key is built like this: (0, BTRFS_DEV_REPLACE_KEY, 0).
*/
#define BTRFS_DEV_REPLACE_KEY 250
/*
* Stores items that allow to quickly map UUIDs to something else.
+ *
* These items are part of the filesystem UUID tree.
* The key is built like this:
* (UUID_upper_64_bits, BTRFS_UUID_KEY*, UUID_lower_64_bits).
@@ -303,8 +321,9 @@
* received subvols */
/*
- * string items are for debugging. They just store a short string of
- * data in the FS
+ * String items are for debugging.
+ *
+ * They just store a short string of data in the FS.
*/
#define BTRFS_STRING_ITEM_KEY 253
@@ -313,7 +332,7 @@
/* 32 bytes in various csum fields */
#define BTRFS_CSUM_SIZE 32
-/* csum types */
+/* Csum types */
enum btrfs_csum_type {
BTRFS_CSUM_TYPE_CRC32 = 0,
BTRFS_CSUM_TYPE_XXHASH = 1,
@@ -322,7 +341,7 @@ enum btrfs_csum_type {
};
/*
- * flags definitions for directory entry item type
+ * Flags definitions for directory entry item type.
*
* Used by:
* struct btrfs_dir_item.type
@@ -347,14 +366,13 @@ enum btrfs_csum_type {
* The key defines the order in the tree, and so it also defines (optimal)
* block layout.
*
- * objectid corresponds to the inode number.
+ * Objectid and offset are interpreted based on type.
+ * While normally for objectid, it either represents a root number, or an
+ * inode number.
*
- * type tells us things about the object, and is a kind of stream selector.
- * so for a given inode, keys with type of 1 might refer to the inode data,
- * type of 2 may point to file data in the btree and type == 3 may point to
- * extents.
- *
- * offset is the starting byte offset for this key in the stream.
+ * Type tells us things about the object, and is a kind of stream selector.
+ * Check the following URL for full references about btrfs_disk_key/btrfs_key:
+ * https://btrfs.wiki.kernel.org/index.php/Btree_Items
*
* btrfs_disk_key is in disk byte order. struct btrfs_key is always
* in cpu native order. Otherwise they are identical and their sizes
@@ -373,49 +391,49 @@ struct btrfs_key {
} __attribute__ ((__packed__));
struct btrfs_dev_item {
- /* the internal btrfs device id */
+ /* The internal btrfs device id */
__le64 devid;
- /* size of the device */
+ /* Size of the device */
__le64 total_bytes;
- /* bytes used */
+ /* Bytes used */
__le64 bytes_used;
- /* optimal io alignment for this device */
+ /* Optimal io alignment for this device */
__le32 io_align;
- /* optimal io width for this device */
+ /* Optimal io width for this device */
__le32 io_width;
- /* minimal io size for this device */
+ /* Minimal io size for this device */
__le32 sector_size;
- /* type and info about this device */
+ /* Type and info about this device */
__le64 type;
- /* expected generation for this device */
+ /* Expected generation for this device */
__le64 generation;
/*
- * starting byte of this partition on the device,
- * to allow for stripe alignment in the future
+ * Starting byte of this partition on the device,
+ * to allow for stripe alignment in the future.
*/
__le64 start_offset;
- /* grouping information for allocation decisions */
+ /* Grouping information for allocation decisions */
__le32 dev_group;
- /* seek speed 0-100 where 100 is fastest */
+ /* Optimal seek speed 0-100 where 100 is fastest */
__u8 seek_speed;
- /* bandwidth 0-100 where 100 is fastest */
+ /* Optimal bandwidth 0-100 where 100 is fastest */
__u8 bandwidth;
- /* btrfs generated uuid for this device */
+ /* Btrfs generated uuid for this device */
__u8 uuid[BTRFS_UUID_SIZE];
- /* uuid of FS who owns this device */
+ /* UUID of FS who owns this device */
__u8 fsid[BTRFS_UUID_SIZE];
} __attribute__ ((__packed__));
@@ -426,30 +444,31 @@ struct btrfs_stripe {
} __attribute__ ((__packed__));
struct btrfs_chunk {
- /* size of this chunk in bytes */
+ /* Size of this chunk in bytes */
__le64 length;
- /* objectid of the root referencing this chunk */
+ /* Objectid of the root referencing this chunk */
__le64 owner;
__le64 stripe_len;
__le64 type;
- /* optimal io alignment for this chunk */
+ /* Optimal io alignment for this chunk */
__le32 io_align;
- /* optimal io width for this chunk */
+ /* Optimal io width for this chunk */
__le32 io_width;
- /* minimal io size for this chunk */
+ /* Minimal io size for this chunk */
__le32 sector_size;
- /* 2^16 stripes is quite a lot, a second limit is the size of a single
- * item in the btree
+ /*
+ * 2^16 stripes is quite a lot, a second limit is the size of a single
+ * item in the btree.
*/
__le16 num_stripes;
- /* sub stripes only matter for raid10 */
+ /* Sub stripes only matter for raid10 */
__le16 sub_stripes;
struct btrfs_stripe stripe;
/* additional stripes go here */
@@ -486,10 +505,9 @@ struct btrfs_free_space_header {
/*
- * items in the extent btree are used to record the objectid of the
- * owner of the block and the number of references
+ * Items in the extent tree are used to record the objectid of the
+ * owner of the block and the number of references.
*/
-
struct btrfs_extent_item {
__le64 refs;
__le64 generation;
@@ -504,14 +522,12 @@ struct btrfs_extent_item_v0 {
#define BTRFS_EXTENT_FLAG_DATA (1ULL << 0)
#define BTRFS_EXTENT_FLAG_TREE_BLOCK (1ULL << 1)
-/* following flags only apply to tree blocks */
-
-/* use full backrefs for extent pointers in the block */
+/* Use full backrefs for extent pointers in the block */
#define BTRFS_BLOCK_FLAG_FULL_BACKREF (1ULL << 8)
/*
- * this flag is only used internally by scrub and may be changed at any time
- * it is only declared here to avoid collisions
+ * This flag is only used internally by scrub and may be changed at any time
+ * it is only declared here to avoid collisions.
*/
#define BTRFS_EXTENT_FLAG_SUPER (1ULL << 48)
@@ -536,7 +552,7 @@ struct btrfs_extent_inline_ref {
__le64 offset;
} __attribute__ ((__packed__));
-/* old style backrefs item */
+/* Old style backrefs item */
struct btrfs_extent_ref_v0 {
__le64 root;
__le64 generation;
@@ -545,9 +561,11 @@ struct btrfs_extent_ref_v0 {
} __attribute__ ((__packed__));
-/* dev extents record free space on individual devices. The owner
- * field points back to the chunk allocation mapping tree that allocated
- * the extent. The chunk tree uuid field is a way to double check the owner
+/* Dev extents record used space on individual devices.
+ *
+ * The owner field points back to the chunk allocation mapping tree that
+ * allocated the extent.
+ * The chunk tree uuid field is a way to double check the owner.
*/
struct btrfs_dev_extent {
__le64 chunk_tree;
@@ -560,7 +578,7 @@ struct btrfs_dev_extent {
struct btrfs_inode_ref {
__le64 index;
__le16 name_len;
- /* name goes here */
+ /* Name goes here */
} __attribute__ ((__packed__));
struct btrfs_inode_extref {
@@ -568,7 +586,7 @@ struct btrfs_inode_extref {
__le64 index;
__le16 name_len;
__u8 name[0];
- /* name goes here */
+ /* Name goes here */
} __attribute__ ((__packed__));
struct btrfs_timespec {
@@ -576,9 +594,7 @@ struct btrfs_timespec {
__le32 nsec;
} __attribute__ ((__packed__));
-/*
- * Inode flags
- */
+/* Inode flags */
#define BTRFS_INODE_NODATASUM (1 << 0)
#define BTRFS_INODE_NODATACOW (1 << 1)
#define BTRFS_INODE_READONLY (1 << 2)
@@ -610,9 +626,9 @@ struct btrfs_timespec {
BTRFS_INODE_ROOT_ITEM_INIT)
struct btrfs_inode_item {
- /* nfs style generation number */
+ /* Nfs style generation number */
__le64 generation;
- /* transid that last touched this inode */
+ /* Transid that last touched this inode */
__le64 transid;
__le64 size;
__le64 nbytes;
@@ -624,12 +640,12 @@ struct btrfs_inode_item {
__le64 rdev;
__le64 flags;
- /* modification sequence number for NFS */
+ /* Modification sequence number for NFS */
__le64 sequence;
/*
- * a little future expansion, for more than this we can
- * just grow the inode item and version it
+ * A little future expansion, for more than this we can just grow the
+ * inode item and version it
*/
__le64 reserved[4];
struct btrfs_timespec atime;
@@ -685,27 +701,25 @@ struct btrfs_root_item {
* mismatching generation values here and thus must invalidate the
* new fields. See btrfs_update_root and btrfs_find_last_root for
* details.
- * the offset of generation_v2 is also used as the start for the memset
+ * The offset of generation_v2 is also used as the start for the memset
* when invalidating the fields.
*/
__le64 generation_v2;
__u8 uuid[BTRFS_UUID_SIZE];
__u8 parent_uuid[BTRFS_UUID_SIZE];
__u8 received_uuid[BTRFS_UUID_SIZE];
- __le64 ctransid; /* updated when an inode changes */
- __le64 otransid; /* trans when created */
- __le64 stransid; /* trans when sent. non-zero for received subvol */
- __le64 rtransid; /* trans when received. non-zero for received subvol */
+ __le64 ctransid; /* Updated when an inode changes */
+ __le64 otransid; /* Trans when created */
+ __le64 stransid; /* Trans when sent. Non-zero for received subvol. */
+ __le64 rtransid; /* Trans when received. Non-zero for received subvol.*/
struct btrfs_timespec ctime;
struct btrfs_timespec otime;
struct btrfs_timespec stime;
struct btrfs_timespec rtime;
- __le64 reserved[8]; /* for future */
+ __le64 reserved[8]; /* For future */
} __attribute__ ((__packed__));
-/*
- * this is used for both forward and backward root refs
- */
+/* This is used for both forward and backward root refs */
struct btrfs_root_ref {
__le64 dirid;
__le64 sequence;
@@ -714,13 +728,14 @@ struct btrfs_root_ref {
struct btrfs_disk_balance_args {
/*
- * profiles to operate on, single is denoted by
- * BTRFS_AVAIL_ALLOC_BIT_SINGLE
+ * Profiles to operate on.
+ *
+ * SINGLE is denoted by BTRFS_AVAIL_ALLOC_BIT_SINGLE.
*/
__le64 profiles;
/*
- * usage filter
+ * Usage filter
* BTRFS_BALANCE_ARGS_USAGE with a single value means '0..N'
* BTRFS_BALANCE_ARGS_USAGE_RANGE - range syntax, min..max
*/
@@ -732,20 +747,21 @@ struct btrfs_disk_balance_args {
};
};
- /* devid filter */
+ /* Devid filter */
__le64 devid;
- /* devid subset filter [pstart..pend) */
+ /* Devid subset filter [pstart..pend) */
__le64 pstart;
__le64 pend;
- /* btrfs virtual address space subset filter [vstart..vend) */
+ /* Btrfs virtual address space subset filter [vstart..vend) */
__le64 vstart;
__le64 vend;
/*
- * profile to convert to, single is denoted by
- * BTRFS_AVAIL_ALLOC_BIT_SINGLE
+ * Profile to convert to.
+ *
+ * SINGLE is denoted by BTRFS_AVAIL_ALLOC_BIT_SINGLE.
*/
__le64 target;
@@ -753,9 +769,9 @@ struct btrfs_disk_balance_args {
__le64 flags;
/*
- * BTRFS_BALANCE_ARGS_LIMIT with value 'limit'
+ * BTRFS_BALANCE_ARGS_LIMIT with value 'limit'.
* BTRFS_BALANCE_ARGS_LIMIT_RANGE - the extend version can use minimum
- * and maximum
+ * and maximum.
*/
union {
__le64 limit;
@@ -767,7 +783,7 @@ struct btrfs_disk_balance_args {
/*
* Process chunks that cross stripes_min..stripes_max devices,
- * BTRFS_BALANCE_ARGS_STRIPES_RANGE
+ * BTRFS_BALANCE_ARGS_STRIPES_RANGE.
*/
__le32 stripes_min;
__le32 stripes_max;
@@ -776,8 +792,8 @@ struct btrfs_disk_balance_args {
} __attribute__ ((__packed__));
/*
- * store balance parameters to disk so that balance can be properly
- * resumed after crash or unmount
+ * Stores balance parameters to disk so that balance can be properly
+ * resumed after crash or unmount.
*/
struct btrfs_balance_item {
/* BTRFS_BALANCE_* */
@@ -806,16 +822,14 @@ enum btrfs_compression_type {
};
struct btrfs_file_extent_item {
- /*
- * transaction id that created this extent
- */
+ /* Transaction id that created this extent */
__le64 generation;
/*
- * max number of bytes to hold this extent in ram
- * when we split a compressed extent we can't know how big
- * each of the resulting pieces will be. So, this is
- * an upper limit on the size of the extent in ram instead of
- * an exact limit.
+ * Max number of bytes to hold this extent in ram.
+ *
+ * When we split a compressed extent we can't know how big each of the
+ * resulting pieces will be. So, this is an upper limit on the size of
+ * the extent in ram instead of an exact limit.
*/
__le64 ram_bytes;
@@ -828,30 +842,34 @@ struct btrfs_file_extent_item {
*/
__u8 compression;
__u8 encryption;
- __le16 other_encoding; /* spare for later use */
+ __le16 other_encoding; /* Spare for later use */
- /* are we inline data or a real extent? */
+ /* Are we inline data or a real extent? */
__u8 type;
/*
- * disk space consumed by the extent, checksum blocks are included
+ * Disk space consumed by the extent, checksum blocks are not included
* in these numbers
*
* At this offset in the structure, the inline extent data start.
*/
__le64 disk_bytenr;
__le64 disk_num_bytes;
+
/*
- * the logical offset in file blocks (no csums)
- * this extent record is for. This allows a file extent to point
- * into the middle of an existing extent on disk, sharing it
- * between two snapshots (useful if some bytes in the middle of the
- * extent have changed
+ * The logical offset inside the file extent.
+ *
+ * This allows a file extent to point into the middle of an existing
+ * extent on disk, sharing it between two snapshots (useful if some
+ * bytes in the middle of the extent have changed).
*/
__le64 offset;
+
/*
- * the logical number of file blocks (no csums included). This
- * always reflects the size uncompressed and without encoding.
+ * The logical number of bytes this file extent is referencing (no
+ * csums included).
+ *
+ * This always reflects the size uncompressed and without encoding.
*/
__le64 num_bytes;
@@ -862,19 +880,19 @@ struct btrfs_csum_item {
} __attribute__ ((__packed__));
enum btrfs_dev_stat_values {
- /* disk I/O failure stats */
+ /* Disk I/O failure stats */
BTRFS_DEV_STAT_WRITE_ERRS, /* EIO or EREMOTEIO from lower layers */
BTRFS_DEV_STAT_READ_ERRS, /* EIO or EREMOTEIO from lower layers */
BTRFS_DEV_STAT_FLUSH_ERRS, /* EIO or EREMOTEIO from lower layers */
- /* stats for indirect indications for I/O failures */
- BTRFS_DEV_STAT_CORRUPTION_ERRS, /* checksum error, bytenr error or
+ /* Stats for indirect indications for I/O failures */
+ BTRFS_DEV_STAT_CORRUPTION_ERRS, /* Checksum error, bytenr error or
* contents is illegal: this is an
* indication that the block was damaged
* during read or write, or written to
* wrong location or read from wrong
* location */
- BTRFS_DEV_STAT_GENERATION_ERRS, /* an indication that blocks have not
+ BTRFS_DEV_STAT_GENERATION_ERRS, /* An indication that blocks have not
* been written */
BTRFS_DEV_STAT_VALUES_MAX
@@ -882,8 +900,8 @@ enum btrfs_dev_stat_values {
struct btrfs_dev_stats_item {
/*
- * grow this item struct at the end for future enhancements and keep
- * the existing values unchanged
+ * Grow this item struct at the end for future enhancements and keep
+ * the existing values unchanged.
*/
__le64 values[BTRFS_DEV_STAT_VALUES_MAX];
} __attribute__ ((__packed__));
@@ -893,8 +911,8 @@ struct btrfs_dev_stats_item {
struct btrfs_dev_replace_item {
/*
- * grow this item struct at the end for future enhancements and keep
- * the existing values unchanged
+ * Grow this item struct at the end for future enhancements and keep
+ * the existing values unchanged.
*/
__le64 src_devid;
__le64 cursor_left;
@@ -908,7 +926,7 @@ struct btrfs_dev_replace_item {
__le64 num_uncorrectable_read_errors;
} __attribute__ ((__packed__));
-/* different types of block groups (and chunks) */
+/* Different types of block groups (and chunks) */
#define BTRFS_BLOCK_GROUP_DATA (1ULL << 0)
#define BTRFS_BLOCK_GROUP_SYSTEM (1ULL << 1)
#define BTRFS_BLOCK_GROUP_METADATA (1ULL << 2)
@@ -1004,20 +1022,16 @@ static inline __u64 btrfs_qgroup_level(__u64 qgroupid)
return qgroupid >> BTRFS_QGROUP_LEVEL_SHIFT;
}
-/*
- * is subvolume quota turned on?
- */
+/* Is subvolume quota turned on? */
#define BTRFS_QGROUP_STATUS_FLAG_ON (1ULL << 0)
-/*
- * RESCAN is set during the initialization phase
- */
+
+/* Is qgroup rescan running? */
#define BTRFS_QGROUP_STATUS_FLAG_RESCAN (1ULL << 1)
+
/*
- * Some qgroup entries are known to be out of date,
- * either because the configuration has changed in a way that
- * makes a rescan necessary, or because the fs has been mounted
- * with a non-qgroup-aware version.
- * Turning qouta off and on again makes it inconsistent, too.
+ * Some qgroup entries are known to be out of date, either because the
+ * configuration has changed in a way that makes a rescan necessary, or
+ * because the fs has been mounted with a non-qgroup-aware version.
*/
#define BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT (1ULL << 2)
@@ -1026,19 +1040,19 @@ static inline __u64 btrfs_qgroup_level(__u64 qgroupid)
struct btrfs_qgroup_status_item {
__le64 version;
/*
- * the generation is updated during every commit. As older
+ * The generation is updated during every commit. As older
* versions of btrfs are not aware of qgroups, it will be
* possible to detect inconsistencies by checking the
- * generation on mount time
+ * generation on mount time.
*/
__le64 generation;
- /* flag definitions see above */
+ /* Flag definitions see above */
__le64 flags;
/*
- * only used during scanning to record the progress
- * of the scan. It contains a logical address
+ * Only used during scanning to record the progress of the scan.
+ * It contains a logical address.
*/
__le64 rescan;
} __attribute__ ((__packed__));
@@ -1052,7 +1066,7 @@ struct btrfs_qgroup_info_item {
} __attribute__ ((__packed__));
/*
- * flags definition for qgroup limits
+ * Flags definition for qgroup limits
*
* Used by:
* struct btrfs_qgroup_limit.flags
@@ -1066,9 +1080,7 @@ struct btrfs_qgroup_info_item {
#define BTRFS_QGROUP_LIMIT_EXCL_CMPR (1ULL << 5)
struct btrfs_qgroup_limit_item {
- /*
- * only updated when any of the other values change
- */
+ /* Only updated when any of the other values change. */
__le64 flags;
__le64 max_rfer;
__le64 max_excl;
@@ -1077,9 +1089,8 @@ struct btrfs_qgroup_limit_item {
} __attribute__ ((__packed__));
/*
- * just in case we somehow lose the roots and are not able to mount,
- * we store an array of the roots from previous transactions
- * in the super.
+ * Just in case we somehow lose the roots and are not able to mount,
+ * we store an array of the roots from previous transactions in the super.
*/
#define BTRFS_NUM_BACKUP_ROOTS 4
struct btrfs_root_backup {
@@ -1118,32 +1129,30 @@ struct btrfs_root_backup {
} __attribute__ ((__packed__));
/*
- * this is a very generous portion of the super block, giving us
- * room to translate 14 chunks with 3 stripes each.
+ * This is a very generous portion of the super block, giving us room to
+ * translate 14 chunks with 3 stripes each.
*/
#define BTRFS_SYSTEM_CHUNK_ARRAY_SIZE 2048
#define BTRFS_LABEL_SIZE 256
-/*
- * the super block basically lists the main trees of the FS
- * it currently lacks any block count etc etc
- */
+
+/* The super block basically lists the main trees of the FS. */
struct btrfs_super_block {
- /* the first 4 fields must match struct btrfs_header */
+ /* The first 4 fields must match struct btrfs_header */
u8 csum[BTRFS_CSUM_SIZE];
/* FS specific UUID, visible to user */
u8 fsid[BTRFS_FSID_SIZE];
__le64 bytenr; /* this block number */
__le64 flags;
- /* allowed to be different from the btrfs_header from here own down */
+ /* Allowed to be different from the btrfs_header from here own down. */
__le64 magic;
__le64 generation;
__le64 root;
__le64 chunk_root;
__le64 log_root;
- /* this will help find the new super based on the log root */
+ /* This will help find the new super based on the log root. */
__le64 log_root_transid;
__le64 total_bytes;
__le64 bytes_used;
@@ -1169,17 +1178,17 @@ struct btrfs_super_block {
__le64 cache_generation;
__le64 uuid_tree_generation;
- /* the UUID written into btree blocks */
+ /* The UUID written into btree blocks */
u8 metadata_uuid[BTRFS_FSID_SIZE];
- /* future expansion */
+ /* Future expansion */
__le64 reserved[28];
u8 sys_chunk_array[BTRFS_SYSTEM_CHUNK_ARRAY_SIZE];
struct btrfs_root_backup super_roots[BTRFS_NUM_BACKUP_ROOTS];
} __attribute__ ((__packed__));
/*
- * feature flags
+ * Feature flags
*
* Used by:
* struct btrfs_super_block::(compat|compat_ro|incompat)_flags
@@ -1205,7 +1214,7 @@ struct btrfs_super_block {
#define BTRFS_FEATURE_INCOMPAT_COMPRESS_ZSTD (1ULL << 4)
/*
- * older kernels tried to do bigger metadata blocks, but the
+ * Older kernels tried to do bigger metadata blocks, but the
* code was pretty buggy. Lets not let them try anymore.
*/
#define BTRFS_FEATURE_INCOMPAT_BIG_METADATA (1ULL << 5)
@@ -1218,8 +1227,10 @@ struct btrfs_super_block {
#define BTRFS_FEATURE_INCOMPAT_RAID1C34 (1ULL << 11)
/*
- * Compat flags that we support. If any incompat flags are set other than the
- * ones specified below then we will fail to mount
+ * Compat flags that we support.
+ *
+ * If any incompat flags are set other than the ones specified below then we
+ * will fail to mount.
*/
#define BTRFS_FEATURE_COMPAT_SUPP 0ULL
#define BTRFS_FEATURE_COMPAT_SAFE_SET 0ULL
@@ -1260,17 +1271,15 @@ struct btrfs_super_block {
#define BTRFS_MAX_LEVEL 8
-/*
- * every tree block (leaf or node) starts with this header.
- */
+/* Every tree block (leaf or node) starts with this header. */
struct btrfs_header {
- /* these first four must match the super block */
+ /* These first four must match the super block */
u8 csum[BTRFS_CSUM_SIZE];
u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
- __le64 bytenr; /* which block this node is supposed to live in */
+ __le64 bytenr; /* Which block this node is supposed to live in */
__le64 flags;
- /* allowed to be different from the super from here on down */
+ /* Allowed to be different from the super from here on down. */
u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
__le64 generation;
__le64 owner;
@@ -1279,8 +1288,8 @@ struct btrfs_header {
} __attribute__ ((__packed__));
/*
- * A leaf is full of items. offset and size tell us where to find
- * the item in the leaf (relative to the start of the data area)
+ * A leaf is full of items. Offset and size tell us where to find
+ * the item in the leaf (relative to the start of the data area).
*/
struct btrfs_item {
struct btrfs_disk_key key;
@@ -1301,8 +1310,8 @@ struct btrfs_leaf {
} __attribute__ ((__packed__));
/*
- * all non-leaf blocks are nodes, they hold only keys and pointers to
- * other blocks
+ * All non-leaf blocks are nodes, they hold only keys and pointers to children
+ * blocks.
*/
struct btrfs_key_ptr {
struct btrfs_disk_key key;
@@ -1315,4 +1324,4 @@ struct btrfs_node {
struct btrfs_key_ptr ptrs[];
} __attribute__ ((__packed__));
-#endif /* _BTRFS_CTREE_H_ */
+#endif /* __BTRFS_TREE_H__ */
Since we're here, modify btrfs_tree.h to follow the latest comment style. This involves: - Use upper case char for the first word - Use one line comment if possible - Add the ending dot if it's a sentence - Add more comment explaining the usage of each tree - Add key type/objectid/offset reference URL - Remove dead comment - Update the header define line to reflect the filename - Add newline to seperate long comment Signed-off-by: Qu Wenruo <wqu@suse.com> --- include/uapi/linux/btrfs_tree.h | 455 ++++++++++++++++---------------- 1 file changed, 232 insertions(+), 223 deletions(-)