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NAMEfs_vxfs — format of a VxFS file system volume SYNOPSIS#include <sys/types.h>
#include <sys/param.h>
#include <sys/fs/vx_fs.h> DESCRIPTIONThe VxFS super-block always begins at byte offset 8192 from the start
of the file system.
The super-block location is fixed so
that various system utilities know where to locate it. Super-block fields contain the following fundamental sizes and
offsets:
- fs_bsize
The block size of the file system.
VxFS supports block sizes of 1024, 2048, 4096,
and 8192 bytes.
The default block size depends on the size of the file
system when you create it. See the bsize
option in
mkfs_vxfs(1M)
for specific values. - fs_ctime
The creation date of the file system.
The
time()
system call supplies the time. - fs_defiextsize
The default size, in blocks, for indirect data extents.
Currently set to 64 by default. - fs_dsize
The number of data blocks in the file system.
A data block is a block which may be
allocated to a file in the file system. - fs_ectime
A placeholder in instances when the creation
date for a file system is expanded for more precision.
Currently zero. - fs_immedlen
The size, in bytes, of the immediate data area in each inode.
Currently 96. - fs_logend
The block address of the last log area block.
You can specify the log area
size with the
mkfs
command.
If not specified,
the default size is 256 blocks for a file system less
than 8 megabytes in size,
1024 blocks for a file system from 8 megabytes to 512 megabytes,
and 16384 blocks for file systems greater than 512 megabytes
in size.
For smaller file systems,
the default is reduced to avoid wasting space. - fs_logstart
The block address of the first log area block.
Currently two. - fs_magic
The magic number
(VX_MAGIC)
for the file system.
This number identifies the file system
as a VxFS file system type. - fs_nau
The number of file system allocation units. - fs_ndaddr
The number of direct extents supported by the
VX_EXT4
mapping type (see the section describing inode list).
Currently 10. - fs_size
The number of blocks,
of size
fs_bsize,
in the file system.
fs_size
is an unsigned 32-bit number,
so the maximum number of blocks in a VxFS file
system is limited to 32 bits. - fs_version
The version number
(VX_VERSION)
of the file system disk layout.
The preceding fields define the size and makeup of the file system.
To reduce
the calculations required in utilities, some of the
values are derived from the fundamental values and
placed in the super-block. The super-block contains the following derived offsets:
- fs_aublocks
The number of data blocks in an allocation unit. - fs_aufirst
The address, in blocks, of the first allocation unit.
There can be a gap between the end of the intent log and the first
allocation unit.
This gap is used to align the first allocation
unit on a desired boundary. - fs_auemlen
The length of a free extent map in blocks. - fs_aulen
The length of an allocation unit in blocks. - fs_aupad
The length, in blocks, of the allocation unit alignment padding. - fs_bmask
A mask value such that
(byte_offset
&
fs_bmask)
rounds
the offset to the nearest smaller block boundary. - fs_boffmask
A mask value such that
(byte_offset
&
fs_boffmask)
yields the offset from the start of the nearest smaller block boundary. - fs_bshift
The log base 2 of
fs_bsize.
Used to convert a byte offset
into a block offset. - fs_bstart
The offset, in blocks, of the first data block
from the start of an allocation unit.
An allocation unit header may contain padding
to align the first data block to a specific boundary. - fs_checksum
A checksum of the above fields.
A macro,
VX_FSCHECKSUM,
verifies or calculates the checksum. - fs_emap
The offset, in blocks, of the free extent map (emap)
from the start of an allocation unit. - fs_fbstart
The offset, in blocks, of the first data block
from the start of the file system. - fs_femap
The offset, in blocks, of the first free extent map (emap)
from the start of the file system. - fs_fimap
The offset, in blocks, of the first free inode map (imap)
from the start of the file system. - fs_iaddrlen
The size, in blocks, of an indirect address block.
An indirect
address block is 8K bytes.
This field is set to (8K /
fs_bsize). - fs_imap
The offset, in blocks, of the free inode map (imap)
from the start of an allocation unit. - fs_inopau
The number of inodes in an allocation unit. - fs_inopb
The number of inode entries per
fs_bsize
block in the inode list.
The VxFS inode is currently 256 bytes long. - fs_inoshift
The log base 2 of fs_inopb.
Used to convert an inode number
into a block offset in the inode list. - fs_maxtier
The log base 2 of fs_aublocks. - fs_nindir
The number of entries in an indirect address extent.
An indirect
address extent is currently 8192 bytes in length, making the
value for
fs_nindir
2048.
The preceding fields are initialized when the file system is created and
do not change unless the file system is resized.
These
fields are replicated in each allocation unit header. The following are additional fields which are dynamic:
- fs_clean
Set to
VX_DIRTY
when a file system is mounted for read/write access.
Set to
VX_CLEAN
on a
umount
or successful
fsck.
The file system cannot be mounted for read/write access unless the
fs_clean
field is
VX_CLEAN. - fs_efree
An array of the current number of free extents of each extent size in the
file system. - fs_firstlogid
Initial log ID for when the file system is mounted. - fs_flags
The following flags are recognized:
- VX_FULLFSCK
Set when a file system requires a full structural check to recover from an
error.
If this flag is set, a full check is performed after the
replay recovery completes. - VX_NOLOG
Set when the file system was mounted with the
VX_MS_NOLOG
option.
If this flag is set, then no log replay recovery is performed. - VX_LOGBAD
Set when an I/O error invalidated the log.
If this flag is set, no log replay recovery is performed. - VX_LOGRESET
Set when the log ID runs over
VX_MAXLOGID
(
2^30
).
The log ID is reset at the next appropriate time
(such as a mount or system sync). - VX_RESIZE
Set when a file system resizing is in progress.
If an
fsck
detects this flag, it performs a resize recovery.
See
fsadm_vxfs(1M)
for a description
of file system expansion. - VX_UPGRADING
Set when a file system upgrade is in progress. If an
fsck
detects this flag, it performs an upgrade recovery.
- fs_fname
File system name (6 characters). - fs_fpack
File system pack label (6 characters). - fs_free
The number of free data blocks. - fs_logversion
The version number of the log format. Set by the
kernel on each mount to ensure that an
fsck
running log replay understands the log format written by the kernel. The log format may change with each release, so all file systems
should be clean before upgrading to a new release. - fs_mod
Set whenever a mounted file system is modified.
It indicates whether the super-block requires rewriting
when a sync operation is performed. - fs_reserved
Reserved for future use. - fs_time
Last time the super-block was written to disk, indicated as the
number of seconds and microseconds
that have elapsed since 0:00:00 GMT January 1, 1970.
The following fields are required by VxFS Version 2
disk layouts and later.
These fields are set when the file system is created and
do not change. They are replicated in each allocation
unit header.
- fs_checksum2
A checksum of fields. - fs_dinosize
The size, in bytes, of a disk inode. Currently 256 bytes. - fs_dniaddr
The number of indirect address levels per inode. - fs_iauimlen
The length, in blocks, of a free inode map in an inode allocation unit. - fs_iausize
The size, in blocks, of an inode allocation unit. - fs_oltsize
The size, in blocks, of the object location table extents pointed to
by
fs_oltext. - fs_oltext
An array of two extent addresses. These extent addresses
point to the two replicated copies of the first object location
table extent.
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