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NAME
     fs_ufs, inode_ufs, inode -  format  of  a  ufs  file  system
     volume

SYNOPSIS
     #include <sys/param.h>

     #include <sys/types.h>

     #include <sys/fs/ufs_fs.h>

     #include <sys/fs/ufs_inode.h>

DESCRIPTION
     Standard UFS file system storage volumes have a common  for-
     mat  for  certain vital information. Every volume is divided
     into a certain number of blocks. The block size is a parame-
     ter  of the file system. Sectors 0 to 15 contain primary and
     secondary bootstrapping programs.

     The actual file system begins at sector 16 with  the  super-
     block.   The  layout  of  the  super-block is defined by the
     header <sys/fs/ufs_fs.h>.

     Each disk drive contains some number of file systems. A file
     system  consists  of  a  number  of  cylinder  groups.  Each
     cylinder group has inodes and data.

     A file system is described by its super-block,  and  by  the
     information  in  the cylinder group blocks.  The super-block
     is critical data and  is  replicated  before  each  cylinder
     group  block  to protect against catastrophic loss.  This is
     done at file system creation time and  the  critical  super-
     block data does not change, so the copies need not be refer-
     enced.

  fs_clean
     fs_clean indicates the state of the file system. The FSCLEAN
     state indicates an undamaged, cleanly unmounted file system.
     The FSACTIVE state indicates a mounted file system that  has
     been  updated.  The FSSTABLE state indicates an idle mounted
     file system.  The FSFIX state  indicates  that  this  fs  is
     mounted, contains inconsistent file system data and is being
     repaired by fsck. The FSBAD state indicates that  this  file
     system  contains  inconsistent  file  system data. It is not
     necessary to run fsck on any unmounted file systems  with  a
     state of FSCLEAN or FSSTABLE. mount(2) will return ENOSPC if
     a UFS file system with a state of FSACTIVE is being  mounted
     for read-write.

     To provide additional safeguard, fs_clean could  be  trusted
     only if fs_state contains a value equal to FSOKAY - fs_time,
     where FSOKAY is a constant integer.  Otherwise, fs_clean  is
     treated as though it contains the value of FSACTIVE.

     Addresses stored in inodes are capable of  addressing  frag-
     ments  of  "blocks."  File  system  blocks  of at most, size
     MAXBSIZE can be optionally broken into 2, 4,  or  8  pieces,
     each  of which is addressable; these pieces may be DEV_BSIZE
     or some multiple of a DEV_BSIZE unit.

     Large files consist exclusively of  large  data  blocks.  To
     avoid  undue  wasted  disk  space,  the last data block of a
     small file is allocated only as many fragments  of  a  large
     block  as are necessary. The file system format retains only
     a single pointer to such a fragment, which is a piece  of  a
     single large block that has been divided. The size of such a
     fragment is determinable  from  information  in  the  inode,
     using the blksize(fs, ip, lbn) macro.

     The file system records space availability at  the  fragment
     level;  aligned  fragments  are  examined to determine block
     availability.

     The root inode is the root of the file system. Inode 0  can-
     not be used for normal purposes and historically, bad blocks
     were linked to inode 1. Thus the root inode is 2 (inode 1 is
     no longer used for this purpose; however numerous dump tapes
     make  this  assumption,  so  we  are  stuck  with  it).  The
     lost+found  directory is given the next available inode when
     it is initially created by mkfs(1M).

  fs_minfree
     fs_minfree gives the minimum acceptable percentage  of  file
     system blocks which may be free. If the freelist drops below
     this level only the  super-user  may  continue  to  allocate
     blocks.  fs_minfree  may  be  set to 0 if no reserve of free
     blocks  is  deemed  necessary,  however  severe  performance
     degradations  will  be observed if the file system is run at
     greater than 90% full; thus the default value of  fs_minfree
     is 10%.

     Empirically the best trade-off between  block  fragmentation
     and  overall disk utilization at a loading of 90% comes with
     a fragmentation of 8; thus the default fragment size  is  an
     eighth of the block size.

  fs_optim
     fs_optim specifies whether the file  system  should  try  to
     minimize  the  time spent allocating blocks, or if it should
     attempt to minimize the space fragmentation on the disk.  If
     the value of fs_minfree is less than 10%, then the file sys-
     tem defaults to optimizing for space to avoid running out of
     full  sized  blocks.   If the value of fs_minfree is greater
     than or equal to 10%, fragmentation is unlikely to be  prob-
     lematical,  and  the  file system defaults to optimizing for
     time.

     Cylinder group related limits: Each cylinder keeps track  of
     the  availability  of  blocks  at different rotational posi-
     tions, so that  sequential  blocks  can  be  laid  out  with
     minimum  rotational latency. fs_nrpos is the number of rota-
     tional positions which are distinguished. With  the  default
     fs_nrpos  of 8, the resolution of the summary information is
     2ms for a typical 3600 rpm drive.

  fs_rotdelay
     fs_rotdelay gives the minimum number of milliseconds to ini-
     tiate  another  disk  transfer  on the same cylinder.  It is
     used in determining the rotationally optimal layout for disk
     blocks  within  a  file;  the  default value for fs_rotdelay
     varies from drive to drive (see tunefs(1M)).

  fs_maxcontig
     fs_maxcontig gives the maximum number of  blocks,  belonging
     to  one  file,  that  will  be allocated contiguously before
     inserting a rotational delay.

     Each file  system  has  a  statically  allocated  number  of
     inodes.  An  inode  is allocated for each NBPI bytes of disk
     space.  The inode allocation strategy is extremely conserva-
     tive.

     MINBSIZE is  the  smallest  allowable  block  size.  With  a
     MINBSIZE of 4096 it is possible to create files of size 2^32
     with only two levels of indirection. MINBSIZE must be  large
     enough  to  hold  a  cylinder  group  block, thus changes to
     (struct cg)  must  keep  its  size  within  MINBSIZE.  Note:
     super-blocks are never more than size SBSIZE.

     The path name on which the file system is mounted  is  main-
     tained  in  fs_fsmnt.  MAXMNTLEN defines the amount of space
     allocated in the super-block for this name.

     The limit on the amount of summary information per file sys-
     tem  is  defined by MAXCSBUFS. It is currently parameterized
     for a maximum of two million cylinders.

     Per cylinder group information is summarized in blocks allo-
     cated  from  the  first  cylinder group's data blocks. These
     blocks are read in from fs_csaddr (size fs_cssize) in  addi-
     tion to the super-block.

     Note: sizeof (struct csum) must be a power of two  in  order
     for the fs_cs macro to work.

     The inode is the focus of all file activity in the file sys-
     tem. There is a unique inode allocated for each active file,
     each current directory, each mounted-on file, text file, and
     the  root.  An inode is "named" by its device/i-number pair.
     For     further     information,     see     the      header
     <sys/fs/ufs_inode.h>.

ATTRIBUTES
     See attributes(5) for a description of the following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Stability Level             | Unstable                    |
    |_____________________________|_____________________________|


SEE ALSO
     fsck_ufs(1M),  mkfs_ufs(1M),  tunefs(1M),  mount(2),  attri-
     butes(5)

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