отлаживать файловую систему XFS (debug an XFS filesystem)
Типы (Types)
This section gives the fields in each structure type and their
meanings. Note that some types of block cover multiple actual
structures, for instance directory blocks.
agf The AGF block is the header for block allocation
information; it is in the second 512-byte block of each
allocation group. The following fields are defined:
magicnum
AGF block magic number, 0x58414746 ('XAGF').
versionnum
version number, currently 1.
seqno sequence number starting from 0.
length size in filesystem blocks of the allocation
group. All allocation groups except the last
one of the filesystem have the superblock's
agblocks value here.
bnoroot
block number of the root of the Btree
holding free space information sorted by
block number.
cntroot
block number of the root of the Btree
holding free space information sorted by
block count.
bnolevel
number of levels in the by-block-number
Btree.
cntlevel
number of levels in the by-block-count
Btree.
flfirst
index into the AGFL block of the first
active entry.
fllast index into the AGFL block of the last active
entry.
flcount
count of active entries in the AGFL block.
freeblks
count of blocks represented in the freespace
Btrees.
longest
longest free space represented in the
freespace Btrees.
btreeblks
number of blocks held in the AGF Btrees.
agfl The AGFL block contains block numbers for use of the block
allocator; it is in the fourth 512-byte block of each
allocation group. Each entry in the active list is a
block number within the allocation group that can be used
for any purpose if space runs low. The AGF block fields
flfirst, fllast, and flcount designate which entries are
currently active. Entry space is allocated in a circular
manner within the AGFL block. Fields defined:
bno array of all block numbers. Even those which
are not active are printed.
agi The AGI block is the header for inode allocation
information; it is in the third 512-byte block of each
allocation group. Fields defined:
magicnum
AGI block magic number, 0x58414749 ('XAGI').
versionnum
version number, currently 1.
seqno sequence number starting from 0.
length size in filesystem blocks of the allocation
group.
count count of inodes allocated.
root block number of the root of the Btree
holding inode allocation information.
level number of levels in the inode allocation
Btree.
freecount
count of allocated inodes that are not in
use.
newino last inode number allocated.
dirino unused.
unlinked
an array of inode numbers within the
allocation group. The entries in the AGI
block are the heads of lists which run
through the inode next_unlinked field. These
inodes are to be unlinked the next time the
filesystem is mounted.
attr An attribute fork is organized as a Btree with the actual
data embedded in the leaf blocks. The root of the Btree is
found in block 0 of the fork. The index (sort order) of
the Btree is the hash value of the attribute name. All
the blocks contain a blkinfo structure at the beginning,
see type dir for a description. Nonleaf blocks are
identical in format to those for version 1 and version 2
directories, see type dir for a description. Leaf blocks
can refer to "local" or "remote" attribute values. Local
values are stored directly in the leaf block. Leaf blocks
contain the following fields:
hdr header containing a blkinfo structure info
(magic number 0xfbee), a count of active
entries, usedbytes total bytes of names and
values, the firstused byte in the name area,
holes set if the block needs compaction, and
array freemap as for dir leaf blocks.
entries
array of structures containing a hashval,
nameidx (index into the block of the name),
and flags incomplete, root, and local.
nvlist array of structures describing the attribute
names and values. Fields always present:
valuelen (length of value in bytes),
namelen, and name. Fields present for local
values: value (value string). Fields present
for remote values: valueblk (fork block
number of containing the value).
Remote values are stored in an independent block in the
attribute fork. Prior to v5, value blocks had no
structure, but in v5 they acquired a header structure with
the following fields:
magic attr3 remote block magic number, 0x5841524d
('XARM').
offset Byte offset of this data block within the
overall attribute value.
bytes Number of bytes stored in this block.
crc Checksum of the attribute block contents.
uuid Filesystem UUID.
owner Inode that owns this attribute value.
bno Block offset of this block within the
inode's attribute fork.
lsn Log serial number of the last time this
block was logged.
data The attribute value data.
bmapbt Files with many extents in their data or attribute fork
will have the extents described by the contents of a Btree
for that fork, instead of being stored directly in the
inode. Each bmap Btree starts with a root block contained
within the inode. The other levels of the Btree are
stored in filesystem blocks. The blocks are linked to
sibling left and right blocks at each level, as well as by
pointers from parent to child blocks. Each block contains
the following fields:
magic bmap Btree block magic number, 0x424d4150
('BMAP').
level level of this block above the leaf level.
numrecs
number of records or keys in the block.
leftsib
left (logically lower) sibling block, 0 if
none.
rightsib
right (logically higher) sibling block, 0 if
none.
recs [leaf blocks only] array of extent records.
Each record contains startoff, startblock,
blockcount, and extentflag (1 if the extent
is unwritten).
keys [non-leaf blocks only] array of key records.
These are the first key value of each block
in the level below this one. Each record
contains startoff.
ptrs [non-leaf blocks only] array of child block
pointers. Each pointer is a filesystem
block number to the next level in the Btree.
bnobt There is one set of filesystem blocks forming the by-
block-number allocation Btree for each allocation group.
The root block of this Btree is designated by the bnoroot
field in the corresponding AGF block. The blocks are
linked to sibling left and right blocks at each level, as
well as by pointers from parent to child blocks. Each
block has the following fields:
magic BNOBT block magic number, 0x41425442
('ABTB').
level level number of this block, 0 is a leaf.
numrecs
number of data entries in the block.
leftsib
left (logically lower) sibling block, 0 if
none.
rightsib
right (logically higher) sibling block, 0 if
none.
recs [leaf blocks only] array of freespace
records. Each record contains startblock and
blockcount.
keys [non-leaf blocks only] array of key records.
These are the first value of each block in
the level below this one. Each record
contains startblock and blockcount.
ptrs [non-leaf blocks only] array of child block
pointers. Each pointer is a block number
within the allocation group to the next
level in the Btree.
cntbt There is one set of filesystem blocks forming the by-
block-count allocation Btree for each allocation group.
The root block of this Btree is designated by the cntroot
field in the corresponding AGF block. The blocks are
linked to sibling left and right blocks at each level, as
well as by pointers from parent to child blocks. Each
block has the following fields:
magic CNTBT block magic number, 0x41425443
('ABTC').
level level number of this block, 0 is a leaf.
numrecs
number of data entries in the block.
leftsib
left (logically lower) sibling block, 0 if
none.
rightsib
right (logically higher) sibling block, 0 if
none.
recs [leaf blocks only] array of freespace
records. Each record contains startblock and
blockcount.
keys [non-leaf blocks only] array of key records.
These are the first value of each block in
the level below this one. Each record
contains blockcount and startblock.
ptrs [non-leaf blocks only] array of child block
pointers. Each pointer is a block number
within the allocation group to the next
level in the Btree.
data User file blocks, and other blocks whose type is unknown,
have this type for display purposes in xfs_db. The block
data is displayed in hexadecimal format.
dir A version 1 directory is organized as a Btree with the
directory data embedded in the leaf blocks. The root of
the Btree is found in block 0 of the file. The index (sort
order) of the Btree is the hash value of the entry name.
All the blocks contain a blkinfo structure at the
beginning with the following fields:
forw next sibling block.
back previous sibling block.
magic magic number for this block type.
The non-leaf (node) blocks have the following fields:
hdr header containing a blkinfo structure info
(magic number 0xfebe), the count of active
entries, and the level of this block above
the leaves.
btree array of entries containing hashval and
before fields. The before value is a block
number within the directory file to the
child block, the hashval is the last hash
value in that block.
The leaf blocks have the following fields:
hdr header containing a blkinfo structure info
(magic number 0xfeeb), the count of active
entries, namebytes (total name string
bytes), holes flag (block needs compaction),
and freemap (array of base, size entries for
free regions).
entries
array of structures containing hashval,
nameidx (byte index into the block of the
name string), and namelen.
namelist
array of structures containing inumber and
name.
dir2 A version 2 directory has four kinds of blocks. Data
blocks start at offset 0 in the file. There are two kinds
of data blocks: single-block directories have the leaf
information embedded at the end of the block, data blocks
in multi-block directories do not. Node and leaf blocks
start at offset 32GiB (with either a single leaf block or
the root node block). Freespace blocks start at offset
64GiB. The node and leaf blocks form a Btree, with
references to the data in the data blocks. The freespace
blocks form an index of longest free spaces within the
data blocks.
A single-block directory block contains the following
fields:
bhdr header containing magic number 0x58443242
('XD2B') and an array bestfree of the
longest 3 free spaces in the block (offset,
length).
bu array of union structures. Each element is
either an entry or a freespace. For
entries, there are the following fields:
inumber, namelen, name, and tag. For
freespace, there are the following fields:
freetag (0xffff), length, and tag. The tag
value is the byte offset in the block of the
start of the entry it is contained in.
bleaf array of leaf entries containing hashval and
address. The address is a 64-bit word
offset into the file.
btail tail structure containing the total count of
leaf entries and stale count of unused leaf
entries.
A data block contains the following fields:
dhdr header containing magic number 0x58443244
('XD2D') and an array bestfree of the
longest 3 free spaces in the block (offset,
length).
du array of union structures as for bu.
Leaf blocks have two possible forms. If the Btree consists
of a single leaf then the freespace information is in the
leaf block, otherwise it is in separate blocks and the
root of the Btree is a node block. A leaf block contains
the following fields:
lhdr header containing a blkinfo structure info
(magic number 0xd2f1 for the single leaf
case, 0xd2ff for the true Btree case), the
total count of leaf entries, and stale count
of unused leaf entries.
lents leaf entries, as for bleaf.
lbests [single leaf only] array of values which
represent the longest freespace in each data
block in the directory.
ltail [single leaf only] tail structure containing
bestcount count of lbests.
A node block is identical to that for types attr and dir.
A freespace block contains the following fields:
fhdr header containing magic number 0x58443246
('XD2F'), firstdb first data block number
covered by this freespace block, nvalid
number of valid entries, and nused number of
entries representing real data blocks.
fbests array of values as for lbests.
dqblk The quota information is stored in files referred to by
the superblock uquotino and pquotino fields. Each
filesystem block in a quota file contains a constant
number of quota entries. The quota entry size is currently
136 bytes, so with a 4KiB filesystem block size there are
30 quota entries per block. The dquot command is used to
locate these entries in the filesystem. The file entries
are indexed by the user or project identifier to determine
the block and offset. Each quota entry has the following
fields:
magic magic number, 0x4451 ('DQ').
version
version number, currently 1.
flags flags, values include 0x01 for user quota,
0x02 for project quota.
id user or project identifier.
blk_hardlimit
absolute limit on blocks in use.
blk_softlimit
preferred limit on blocks in use.
ino_hardlimit
absolute limit on inodes in use.
ino_softlimit
preferred limit on inodes in use.
bcount blocks actually in use.
icount inodes actually in use.
itimer time when service will be refused if soft
limit is violated for inodes.
btimer time when service will be refused if soft
limit is violated for blocks.
iwarns number of warnings issued about inode limit
violations.
bwarns number of warnings issued about block limit
violations.
rtb_hardlimit
absolute limit on realtime blocks in use.
rtb_softlimit
preferred limit on realtime blocks in use.
rtbcount
realtime blocks actually in use.
rtbtimer
time when service will be refused if soft
limit is violated for realtime blocks.
rtbwarns
number of warnings issued about realtime
block limit violations.
inobt There is one set of filesystem blocks forming the inode
allocation Btree for each allocation group. The root block
of this Btree is designated by the root field in the
corresponding AGI block. The blocks are linked to sibling
left and right blocks at each level, as well as by
pointers from parent to child blocks. Each block has the
following fields:
magic INOBT block magic number, 0x49414254
('IABT').
level level number of this block, 0 is a leaf.
numrecs
number of data entries in the block.
leftsib
left (logically lower) sibling block, 0 if
none.
rightsib
right (logically higher) sibling block, 0 if
none.
recs [leaf blocks only] array of inode records.
Each record contains startino allocation-
group relative inode number, freecount count
of free inodes in this chunk, and free
bitmap, LSB corresponds to inode 0.
keys [non-leaf blocks only] array of key records.
These are the first value of each block in
the level below this one. Each record
contains startino.
ptrs [non-leaf blocks only] array of child block
pointers. Each pointer is a block number
within the allocation group to the next
level in the Btree.
inode Inodes are allocated in "chunks" of 64 inodes each.
Usually a chunk is multiple filesystem blocks, although
there are cases with large filesystem blocks where a chunk
is less than one block. The inode Btree (see inobt above)
refers to the inode numbers per allocation group. The
inode numbers directly reflect the location of the inode
block on disk. Use the inode command to point xfs_db to a
specific inode. Each inode contains four regions: core,
next_unlinked, u, and a. core contains the fixed
information. next_unlinked is separated from the core due
to journaling considerations, see type agi field unlinked.
u is a union structure that is different in size and
format depending on the type and representation of the
file data ("data fork"). a is an optional union structure
to describe attribute data, that is different in size,
format, and location depending on the presence and
representation of attribute data, and the size of the u
data ("attribute fork"). xfs_db automatically selects the
proper union members based on information in the inode.
The following are fields in the inode core:
magic inode magic number, 0x494e ('IN').
mode mode and type of file, as described in
chmod(2), mknod(2), and stat(2).
version
inode version, 1 or 2.
format format of u union data (0: xfs_dev_t, 1:
local file - in-inode directory or symlink,
2: extent list, 3: Btree root, 4: unique id
[unused]).
nlinkv1
number of links to the file in a version 1
inode.
nlinkv2
number of links to the file in a version 2
inode.
projid_lo
owner's project id (low word; version 2
inode only). projid_hi owner's project id
(high word; version 2 inode only).
uid owner's user id.
gid owner's group id.
atime time last accessed (seconds and
nanoseconds).
mtime time last modified.
ctime time created or inode last modified.
size number of bytes in the file.
nblocks
total number of blocks in the file including
indirect and attribute.
extsize
basic/minimum extent size for the file.
nextents
number of extents in the data fork.
naextents
number of extents in the attribute fork.
forkoff
attribute fork offset in the inode, in
64-bit words from the start of u.
aformat
format of a data (1: local attribute data,
2: extent list, 3: Btree root).
dmevmask
DMAPI event mask.
dmstate
DMAPI state information.
newrtbm
file is the realtime bitmap and is "new"
format.
prealloc
file has preallocated data space after EOF.
realtime
file data is in the realtime subvolume.
gen inode generation number.
The following fields are in the u data fork union:
bmbt bmap Btree root. This looks like a bmapbtd
block with redundant information removed.
bmx array of extent descriptors.
dev dev_t for the block or character device.
sfdir shortform (in-inode) version 1 directory.
This consists of a hdr containing the parent
inode number and a count of active entries
in the directory, followed by an array list
of hdr.count entries. Each such entry
contains inumber, namelen, and name string.
sfdir2 shortform (in-inode) version 2 directory.
This consists of a hdr containing a count of
active entries in the directory, an i8count
of entries with inumbers that don't fit in a
32-bit value, and the parent inode number,
followed by an array list of hdr.count
entries. Each such entry contains namelen, a
saved offset used when the directory is
converted to a larger form, a name string,
and the inumber.
symlink
symbolic link string value.
The following fields are in the a attribute fork union if
it exists:
bmbt bmap Btree root, as above.
bmx array of extent descriptors.
sfattr shortform (in-inode) attribute values. This
consists of a hdr containing a totsize
(total size in bytes) and a count of active
entries, followed by an array list of
hdr.count entries. Each such entry contains
namelen, valuelen, root flag, name, and
value.
log Log blocks contain the journal entries for XFS. It's not
useful to examine these with xfs_db, use xfs_logprint(8)
instead.
refcntbt
There is one set of filesystem blocks forming the
reference count Btree for each allocation group. The root
block of this Btree is designated by the refcntroot field
in the corresponding AGF block. The blocks are linked to
sibling left and right blocks at each level, as well as by
pointers from parent to child blocks. Each block has the
following fields:
magic REFC block magic number, 0x52334643
('R3FC').
level level number of this block, 0 is a leaf.
numrecs
number of data entries in the block.
leftsib
left (logically lower) sibling block, 0 if
none.
rightsib
right (logically higher) sibling block, 0 if
none.
recs [leaf blocks only] array of reference count
records. Each record contains startblock,
blockcount, and refcount.
keys [non-leaf blocks only] array of key records.
These are the first value of each block in
the level below this one. Each record
contains startblock.
ptrs [non-leaf blocks only] array of child block
pointers. Each pointer is a block number
within the allocation group to the next
level in the Btree.
rmapbt There is one set of filesystem blocks forming the reverse
mapping Btree for each allocation group. The root block of
this Btree is designated by the rmaproot field in the
corresponding AGF block. The blocks are linked to sibling
left and right blocks at each level, as well as by
pointers from parent to child blocks. Each block has the
following fields:
magic RMAP block magic number, 0x524d4233
('RMB3').
level level number of this block, 0 is a leaf.
numrecs
number of data entries in the block.
leftsib
left (logically lower) sibling block, 0 if
none.
rightsib
right (logically higher) sibling block, 0 if
none.
recs [leaf blocks only] array of reference count
records. Each record contains startblock,
blockcount, owner, offset, attr_fork,
bmbt_block, and unwritten.
keys [non-leaf blocks only] array of double-key
records. The first ("low") key contains the
first value of each block in the level below
this one. The second ("high") key contains
the largest key that can be used to identify
any record in the subtree. Each record
contains startblock, owner, offset,
attr_fork, and bmbt_block.
ptrs [non-leaf blocks only] array of child block
pointers. Each pointer is a block number
within the allocation group to the next
level in the Btree.
rtbitmap
If the filesystem has a realtime subvolume, then the
rbmino field in the superblock refers to a file that
contains the realtime bitmap. Each bit in the bitmap file
controls the allocation of a single realtime extent (set
== free). The bitmap is processed in 32-bit words, the LSB
of a word is used for the first extent controlled by that
bitmap word. The atime field of the realtime bitmap inode
contains a counter that is used to control where the next
new realtime file will start.
rtsummary
If the filesystem has a realtime subvolume, then the
rsumino field in the superblock refers to a file that
contains the realtime summary data. The summary file
contains a two-dimensional array of 16-bit values. Each
value counts the number of free extent runs (consecutive
free realtime extents) of a given range of sizes that
starts in a given bitmap block. The size ranges are
binary buckets (low size in the bucket is a power of 2).
There are as many size ranges as are necessary given the
size of the realtime subvolume. The first dimension is
the size range, the second dimension is the starting
bitmap block number (adjacent entries are for the same
size, adjacent bitmap blocks).
sb There is one sb (superblock) structure per allocation
group. It is the first disk block in the allocation
group. Only the first one (block 0 of the filesystem) is
actually used; the other blocks are redundant information
for xfs_repair(8) to use if the first superblock is
damaged. Fields defined:
magicnum
superblock magic number, 0x58465342
('XFSB').
blocksize
filesystem block size in bytes.
dblocks
number of filesystem blocks present in the
data subvolume.
rblocks
number of filesystem blocks present in the
realtime subvolume.
rextents
number of realtime extents that rblocks
contain.
uuid unique identifier of the filesystem.
logstart
starting filesystem block number of the log
(journal). If this value is 0 the log is
"external".
rootino
root inode number.
rbmino realtime bitmap inode number.
rsumino
realtime summary data inode number.
rextsize
realtime extent size in filesystem blocks.
agblocks
size of an allocation group in filesystem
blocks.
agcount
number of allocation groups.
rbmblocks
number of realtime bitmap blocks.
logblocks
number of log blocks (filesystem blocks).
versionnum
filesystem version information. This value
is currently 1, 2, 3, or 4 in the low 4
bits. If the low bits are 4 then the other
bits have additional meanings. 1 is the
original value. 2 means that attributes
were used. 3 means that version 2 inodes
(large link counts) were used. 4 is the
bitmask version of the version number. In
this case, the other bits are used as flags
(0x0010: attributes were used, 0x0020:
version 2 inodes were used, 0x0040: quotas
were used, 0x0080: inode cluster alignment
is in force, 0x0100: data stripe alignment
is in force, 0x0200: the shared_vn field is
used, 0x1000: unwritten extent tracking is
on, 0x2000: version 2 directories are in
use).
sectsize
sector size in bytes, currently always 512.
This is the size of the superblock and the
other header blocks.
inodesize
inode size in bytes.
inopblock
number of inodes per filesystem block.
fname obsolete, filesystem name.
fpack obsolete, filesystem pack name.
blocklog
log2 of blocksize.
sectlog
log2 of sectsize.
inodelog
log2 of inodesize.
inopblog
log2 of inopblock.
agblklog
log2 of agblocks (rounded up).
rextslog
log2 of rextents.
inprogress
mkfs.xfs(8) or xfs_copy(8) aborted before
completing this filesystem.
imax_pct
maximum percentage of filesystem space used
for inode blocks.
icount number of allocated inodes.
ifree number of allocated inodes that are not in
use.
fdblocks
number of free data blocks.
frextents
number of free realtime extents.
uquotino
user quota inode number.
pquotino
project quota inode number; this is
currently unused.
qflags quota status flags (0x01: user quota
accounting is on, 0x02: user quota limits
are enforced, 0x04: quotacheck has been run
on user quotas, 0x08: project quota
accounting is on, 0x10: project quota limits
are enforced, 0x20: quotacheck has been run
on project quotas).
flags random flags. 0x01: only read-only mounts
are allowed.
shared_vn
shared version number (shared readonly
filesystems).
inoalignmt
inode chunk alignment in filesystem blocks.
unit stripe or RAID unit.
width stripe or RAID width.
dirblklog
log2 of directory block size (filesystem
blocks).
symlink
Symbolic link blocks are used only when the symbolic link
value does not fit inside the inode. The block content is
just the string value. Bytes past the logical end of the
symbolic link value have arbitrary values.
text User file blocks, and other blocks whose type is unknown,
have this type for display purposes in xfs_db. The block
data is displayed in two columns: Hexadecimal format and
printable ASCII chars.
