BSD 4_4 release

[unix-history] / usr / src / share / man / man5 / fs.5

diff --git a/usr/src/share/man/man5/fs.5 b/usr/src/share/man/man5/fs.5
index bb5865d..ae0f62f 100644 (file)
--- a/usr/src/share/man/man5/fs.5
+++ b/usr/src/share/man/man5/fs.5
@@ -1,37 +1,76 @@
-.\" Copyright (c) 1983 Regents of the University of California.
-.\" All rights reserved.  The Berkeley software License Agreement
-.\" specifies the terms and conditions for redistribution.
+.\" Copyright (c) 1983, 1991, 1993
+.\"    The Regents of the University of California.  All rights reserved.

 .\"
 .\"

-.\"    @(#)fs.5        6.3 (Berkeley) 5/2/88
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"    This product includes software developed by the University of
+.\"    California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.

 .\"
 .\"

-.TH FS 5 "May 2, 1988"
-.UC 5
-.SH NAME
-fs, inode \- format of file system volume
-.SH SYNOPSIS
-.B #include <sys/types.h>
-.br
-.B #include <sys/fs.h>
-.br
-.B #include <sys/inode.h>
-.SH DESCRIPTION
-Every file system storage volume (disk, nine-track tape, for instance)
-has a common format for certain vital information.
-Every such volume is divided into a certain number of blocks.
-The block size is a parameter of the file system.
-Sectors beginning at BBLOCK and continuing for BBSIZE are used to
-contain a label and for some hardware
-primary and secondary bootstrapping programs.
-.PP
-The actual file system begins at sector SBLOCK with the
-.I "super block"
-that is of size SBSIZE.
-The layout of the super block as defined by the include file
-.RI < sys/fs.h >
-is:
-.PP
-.nf
-.ta \w'\ \ \ \ 'u +\w'daddr_t\ \ 'u +\w'fs_fsmnt[MAXMNTLEN];\ \ 'u
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)fs.5       8.1 (Berkeley) 6/5/93
+.\"
+.Dd June 5, 1993
+.Dt FS 5
+.Os BSD 4.2
+.Sh NAME
+.Nm fs ,
+.Nm inode
+.Nd format of file system volume
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <ufs/fs.h>
+.Fd #include <ufs/inode.h>
+.Sh DESCRIPTION
+The files
+.Aq Pa fs.h
+and
+.Aq Pa inode.h
+declare several structures, defined variables and macros
+which are used to create and manage the underlying format of
+file system objects on random access devices (disks).
+.Pp
+The block size and number of blocks which
+comprise a file system are parameters of the file system.
+Sectors beginning at
+.Dv BBLOCK
+and continuing for
+.Dv BBSIZE
+are used
+for a disklabel and for some hardware primary
+and secondary bootstrapping programs.
+.Pp
+The actual file system begins at sector
+.Dv SBLOCK
+with the
+.Em super-block
+that is of size
+.Dv SBSIZE .
+The following structure described the super-block and is
+from the file
+.Aq Pa ufs/fs.h :
+.Bd -literal

 #define        FS_MAGIC 0x011954
 struct fs {
        struct  fs *fs_link;    /* linked list of file systems */
 #define        FS_MAGIC 0x011954
 struct fs {
        struct  fs *fs_link;    /* linked list of file systems */


@@ -108,7 +147,7 @@ struct fs {
        long    fs_sparecon[56];        /* reserved for future constants */
        quad    fs_qbmask;      /* ~fs_bmask - for use with quad size */
        quad    fs_qfmask;      /* ~fs_fmask - for use with quad size */
        long    fs_sparecon[56];        /* reserved for future constants */
        quad    fs_qbmask;      /* ~fs_bmask - for use with quad size */
        quad    fs_qfmask;      /* ~fs_fmask - for use with quad size */

-       long    fs_postblformat;        /* format of positional layout tables */
+       long    fs_postblformat; /* format of positional layout tables */

        long    fs_nrpos;       /* number of rotaional positions */
        long    fs_postbloff;   /* (short) rotation block list head */
        long    fs_rotbloff;    /* (u_char) blocks for each rotation */
        long    fs_nrpos;       /* number of rotaional positions */
        long    fs_postbloff;   /* (short) rotation block list head */
        long    fs_rotbloff;    /* (u_char) blocks for each rotation */


@@ -116,12 +155,12 @@ struct fs {
        u_char  fs_space[1];    /* list of blocks for each rotation */
 /* actually longer */
 };
        u_char  fs_space[1];    /* list of blocks for each rotation */
 /* actually longer */
 };

-.fi
-.LP
+.Ed
+.Pp

 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.
 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.

-.LP
+.Pp

 A file system is described by its super-block, which in turn
 describes the cylinder groups.  The super-block is critical
 data and is replicated in each cylinder group to protect against
 A file system is described by its super-block, which in turn
 describes the cylinder groups.  The super-block is critical
 data and is replicated in each cylinder group to protect against


@@ -129,49 +168,61 @@ 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
 referenced further unless disaster strikes.
 time and the critical
 super-block data does not change, so the copies need not be
 referenced further unless disaster strikes.

-.LP
+.Pp

 Addresses stored in inodes are capable of addressing fragments
 Addresses stored in inodes are capable of addressing fragments

-of `blocks'. File system blocks of at most size MAXBSIZE can 
+of `blocks'. File system blocks of at most size
+.Dv MAXBSIZE
+can 

 be optionally broken into 2, 4, or 8 pieces, each of which is
 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.
-.LP
+addressable; these pieces may be
+.Dv DEV_BSIZE ,
+or some multiple of
+a
+.Dv DEV_BSIZE
+unit.
+.Pp

 Large files consist of exclusively large data blocks.  To avoid
 undue wasted disk space, the last data block of a small file is
 allocated as 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
 Large files consist of exclusively large data blocks.  To avoid
 undue wasted disk space, the last data block of a small file is
 allocated as 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.
-.LP
+information in the inode, using the
+.Fn blksize fs ip lbn
+macro.
+.Pp

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

-.LP
+.Pp

 The root inode is the root of the file system.
 Inode 0 can't 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 root inode is the root of the file system.
 Inode 0 can't 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).

-.LP
-.I fs_minfree
-gives the minimum acceptable percentage of file system
+.Pp
+The
+.Fa fs_minfree
+element gives the minimum acceptable percentage of file system

 blocks that may be free. If the freelist drops below this level
 only the super-user may continue to allocate blocks.
 blocks that may be free. If the freelist drops below this level
 only the super-user may continue to allocate blocks.

-.I Fs_minfree
+The
+.Fa fs_minfree
+element

 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
 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

-.I fs_minfree
+.Fa fs_minfree

 is 10%.
 is 10%.

-.LP
+.Pp

 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.
 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.

-.LP
-.I fs_optim
+.Pp
+The element
+.Fa 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.
 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.


@@ -181,83 +232,111 @@ running out of full sized blocks.
 If the value of minfree is greater than or equal to 10%,
 fragmentation is unlikely to be problematical, and
 the file system defaults to optimizing for time.
 If the value of minfree is greater than or equal to 10%,
 fragmentation is unlikely to be problematical, and
 the file system defaults to optimizing for time.

-.LP
-.I Cylinder group related
-.IR limits :
+.Pp
+.Em Cylinder group related limits :

 Each cylinder keeps track of the availability of blocks at different
 rotational positions, so that sequential blocks can be laid out
 with minimum rotational latency. With the default of 8 distinguished
 rotational positions, the resolution of the
 summary information is 2ms for a typical 3600 rpm drive.
 Each cylinder keeps track of the availability of blocks at different
 rotational positions, so that sequential blocks can be laid out
 with minimum rotational latency. With the default of 8 distinguished
 rotational positions, the resolution of the
 summary information is 2ms for a typical 3600 rpm drive.

-.LP
-.I fs_rotdelay
+.Pp
+The element
+.Fa fs_rotdelay

 gives the minimum number of milliseconds to initiate
 gives the minimum number of milliseconds to initiate

-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
-.I fs_rotdelay
+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
+.Fa fs_rotdelay

 is 2ms.
 is 2ms.

-.LP
+.Pp

 Each file system has a statically allocated number of inodes.
 Each file system has a statically allocated number of inodes.

-An inode is allocated for each NBPI bytes of disk space.
+An inode is allocated for each
+.Dv NBPI
+bytes of disk space.

 The inode allocation strategy is extremely conservative.
 The inode allocation strategy is extremely conservative.

-.LP
-MINBSIZE is the smallest allowable block size.
-With a MINBSIZE of 4096
+.Pp
+.Dv MINBSIZE
+is the smallest allowable block size.
+With a
+.Dv MINBSIZE
+of 4096

 it is possible to create files of size
 2^32 with only two levels of indirection.
 it is possible to create files of size
 2^32 with only two levels of indirection.

-MINBSIZE must be big enough to hold a cylinder group block,
-thus changes to (struct cg) must keep its size within MINBSIZE.
-Note that super blocks are never more than size SBSIZE.
-.LP
+.Dv MINBSIZE
+must be big enough to hold a cylinder group block,
+thus changes to
+.Pq Fa struct cg
+must keep its size within
+.Dv MINBSIZE .
+Note that super-blocks are never more than size
+.Dv SBSIZE .
+.Pp

 The path name on which the file system is mounted is maintained in
 The path name on which the file system is mounted is maintained in

-.IR fs_fsmnt .
-MAXMNTLEN defines the amount of space allocated in 
-the super block for this name.
+.Fa fs_fsmnt .
+.Dv MAXMNTLEN
+defines the amount of space allocated in 
+the super-block for this name.

 The limit on the amount of summary information per file system
 The limit on the amount of summary information per file system

-is defined by MAXCSBUFS.
+is defined by
+.Dv MAXCSBUFS.

 For a 4096 byte block size, it is currently parameterized for a
 maximum of two million cylinders.
 For a 4096 byte block size, it is currently parameterized for a
 maximum of two million cylinders.

-.LP
+.Pp

 Per cylinder group information is summarized in blocks allocated
 from the first cylinder group's data blocks. 
 These blocks are read in from
 Per cylinder group information is summarized in blocks allocated
 from the first cylinder group's data blocks. 
 These blocks are read in from

-.I fs_csaddr
+.Fa fs_csaddr

 (size
 (size

-.IR fs_cssize )
-in addition to the super block.
-.LP
-.B N.B.:
-sizeof (struct csum) must be a power of two in order for
-the ``fs_cs'' macro to work.
-.LP
-.I Super block for a file
-.IR system :
+.Fa fs_cssize )
+in addition to the super-block.
+.Pp
+.Sy N.B.:
+.Xr sizeof Pq Fa struct csum
+must be a power of two in order for
+the
+.Fn fs_cs
+macro to work.
+.Pp
+The
+.Em "Super-block for a file system" :

 The size of the rotational layout tables
 The size of the rotational layout tables

-is limited by the fact that the super block is of size SBSIZE.
+is limited by the fact that the super-block is of size
+.Dv SBSIZE .

 The size of these tables is
 The size of these tables is

-.B inversely
+.Em inversely

 proportional to the block
 size of the file system. The size of the tables is
 increased when sector sizes are not powers of two,
 as this increases the number of cylinders
 proportional to the block
 size of the file system. The size of the tables is
 increased when sector sizes are not powers of two,
 as this increases the number of cylinders

-included before the rotational pattern repeats (
-.IR fs_cpc ).
+included before the rotational pattern repeats
+.Pq Fa fs_cpc .

 The size of the rotational layout
 The size of the rotational layout

-tables is derived from the number of bytes remaining in (struct fs).
-.LP
+tables is derived from the number of bytes remaining in
+.Pq Fa struct fs .
+.Pp

 The number of blocks of data per cylinder group
 is limited because cylinder groups are at most one block.
 The inode and free block tables
 must fit into a single block after deducting space for
 The number of blocks of data per cylinder group
 is limited because cylinder groups are at most one block.
 The inode and free block tables
 must fit into a single block after deducting space for

-the cylinder group structure (struct cg).
-.LP
-.IR Inode :
+the cylinder group structure
+.Pq Fa struct cg .
+.Pp
+The
+.Em Inode :

 The inode is the focus of all file activity in the
 The inode is the focus of all file activity in the

-UNIX file system.  There is a unique inode allocated
+.Tn UNIX
+file system.
+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 include file
 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 include file

-.RI < sys/inode.h >.
+.Aq Pa sys/inode.h .
+.Sh HISTORY
+A super-block structure named filsys appeared in
+.At v6 .
+The file system described in this manual appeared
+in
+.Bx 4.2 .