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fs.5: format under UNIX-7 roff!

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mention boot & swap track locations
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phil
2019-10-30 01:34:25 -04:00
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@@ -4,109 +4,128 @@ NAME format of file system
.sp .sp
SYNOPSIS -- SYNOPSIS --
.sp .sp
DESCRIPTION The RB09 fixed head disk has 8,000 64-word DESCRIPTION
blocks on each of its two surfaces. Unix uses .in 8
the second surface (physical blocks 8,000 to The RB09 fixed head disk has 8,000 64-word
15,999) and numbers them from logical block 0 to blocks (100 tracks of 80 bloocks)
logical block 7,999. The following discussion on each of its two surfaces. The Unix filesystem
refers to logical blocks. is stored in the first 80 tracks of
the second surface (physical blocks 8,000 to
14,399 -- physical tracks 100 to 179)
and numbers them from logical block 0 to
logical block 6,399.
.sp .sp
The Unix filesystem is divided into 8,000 blocks The Unix filesystem is divided into 6,400 logical blocks
of 64 words per block. Block 0 is the "sysdata" of 64 words per block. Block 0 is the "sysdata"
block. The first word points to the first block block. The first word points to the first block
of the free-storage map. Each block in the of the free-storage map. Each block in the
free-storage map is structured as follows: the free-storage map is structured as follows: the
first word is the block number of the next block first word is the block number of the next block
in the free-storage map, or zero if this is the in the free-storage map, or zero if this is the
end of the free-storage map. The next nine words end of the free-storage map. The next nine words
hold free block numbers, or zero (no block hold free block numbers, or zero (no block
number). number).
.sp .sp
Block 1 on the filesystem is unused. (?) Block 1 on the filesystem is unused. (?)
.sp .sp
I-numbers begin at 1, and the storage for I-numbers begin at 1, and the storage for
i-nodes begins at block 2. Blocks 2 to 711 i-nodes begins at block 2. Blocks 2 to 711
contain the i-nodes, with five consecutive contain the i-nodes, with five 12-word
i-nodes per block. Certain i-nodes are reserved i-nodes per block. Certain i-nodes are reserved
for special files, directories and devices: for special files, directories and devices:
.sp .sp
1 The core file written by "sys save" or a .nf
bad system call 1 The core file written by "sys save"
2 The "dd" directory directory or a bad system call
3 The "system" directory 2 The "dd" directory directory
6 The "ttyin" special file 3 The "system" directory
7 The "keyboard" (graphic-2) special file 6 The "ttyin" special file
8 The "pptin" (paper tape reader) special 7 The "keyboard" (GRAPHIC-2)
file special file
10 The "ttyout" special file 8 The "pptin" (paper tape reader)
11 The "display" (graphic-2) special file special file
12 The "pptout" (paper tape punch) special 10 The "ttyout" special file
file 11 The "display" (GRAPHIC-2)
special file
12 The "pptout" (paper tape punch)
special file
.fi
.sp .sp
There is only one file system which is always There is only one file system which is always
mounted; it resides on the RB disk. This device mounted; it resides on the RB disk.
is also used for swapping. The swap areas are at
the high blocks on this device: blocks 6,400 to
7,999. These blocks do not appear in the free
list.
.sp .sp
Each i-node represents one file. The format of The last twenty tracks of the second disk surface
an i-node is as follows, where the left column are use for bootable images and swapping:
represents the offset in words from the
beginning of the i-node:
.sp .sp
0 flags (see below) Each physical track from 180 to 189
1 first indirect block or contents block contains a bootable system image of 3K words.
...
7 seventh indirect block or contents block
8 user ID of owner
9 link count
10 size in words
11 unique value assigned at creation
.sp .sp
The flags are as follows: Each physical track from 190 to 199 is used to swap
a user process (4K words plus a 64-word swapable
"userdata" area).
.sp .sp
400000 i-node is allocated Each i-node represents one file. The format of
200000 large file an i-node is as follows, where the left column
?????? allocated bit (always on) represents the offset in words from the
000040 special file beginning of the i-node:
000020 directory
000010 read, owner
000004 write, owner
000002 read, non-owner
000001 write, non-owner
.sp .sp
The allocated bit (flag ??????) is believed even .nf
if the i-node map says the i-node is free; thus 0 flags (see below)
corruption of the map may cause i-nodes to 1 first indirect block or data block
become unallocatable, but will not cause active ...
nodes to be reused. 7 seventh indirect block or data block
8 user ID of owner
9 link count
10 size in words
11 unique value assigned at creation
.sp .sp
Word number n of a file is accessed as follows: .in 8
n is divided by 64 to find its logical block The flags are as follows:
number (say b) in the file. If the file is small
(flag 200000 is 0), then b must be less than 7,
and the physical block number corresponding to b
is the bth entry in the address portion of the
i-node.
.sp .sp
If the file is large, b is divided by 64 to 400000 i-node is allocated
yield a number which must be less than 8 (or 200000 large file
the file is too large for UNIX to handle). ?????? allocated bit (always on)
The corresponding slot in the i-node address 000040 special file
portion gives the physical block number of an 000020 directory
indirect block. The residue mod 64 gives a 000010 read, owner
word offset in the indirect block, and the 000004 write, owner
word found there is the physical address of 000002 read, non-owner
the block corresponding to b. 000001 write, non-owner
.fi
.in 8
.sp .sp
If block b in a file exists, it is not necessary The allocated bit (flag ??????) is believed even
that all blocks less than b exist. A zero block if the i-node map says the i-node is free; thus
number either in the address words of the i-node corruption of the map may cause i-nodes to
or in an indirect block indicates that the become unallocatable, but will not cause active
corresponding block has never been allocated. nodes to be reused.
Such a missing block reads as if it contained .sp
all zero words. Word number n of a file is accessed as follows:
n is divided by 64 to find its logical block
number (say b) in the file. If the file is small
(flag 200000 is 0), then b must be less than 7,
and the physical block number corresponding to b
is the bth entry in the address portion of the
i-node.
.sp
If the file is large, b is divided by 64 to
yield a number which must be less than 8 (or
the file is too large for UNIX to handle).
The corresponding slot in the i-node address
portion gives the physical block number of an
indirect block. The residue mod 64 gives a
word offset in the indirect block, and the
word found there is the physical address of
the block corresponding to b.
.sp
If block b in a file exists, it is not necessary
that all blocks less than b exist. A zero block
number either in the address words of the i-node
or in an indirect block indicates that the
corresponding block has never been allocated.
Such a missing block reads as if it contained
all zero words.
.in 0
.sp .sp
FILES -- FILES --
.sp .sp