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tab(HW)


tab -- kernel tables pseudo-device driver

Description

The kernel tables driver is a character special pseudo-device providing access to various strings (such as console messages) and system tables (such as all processes). Commands such as ps(C) use this device to avoid having to understand how all of kernel memory is laid out.

The strings are described in string(HW); this manual page describes only the system tables.

Each table comprises zero or more entries (elements). An element is usually a structure defined in a system header file. The elements in a given table do not have to be the same size, and in this release of the Operating System, all tables are read-only. (Some of the strings are writable.)

The minor device number determines which kernel table is read.

There are two read modes:


Element-by-element
Each read(S) returns the next element in the table. If the number of bytes requested is smaller than that element's size, the trailing end of the element is not read. If the number of bytes is larger, only the bytes comprising the element are read. If the current position in the table is not at the start of an element, it is automatically advanced to the start of the subsequent element before any bytes are read. This is the default mode for most tables.

Byte-stream
Each read returns the requested number of bytes starting at the current position in the table but not extending beyond its end. The data read may start or end in the middle of an element, and may contain part or all of one or more elements. This mode is used when the device is opened using open(S) and O_SYNC is specified, or a subsequent call to fcntl(S) sets the O_SYNC mode. For some tables (and all the strings) this is the default and only read mode.
The end of the table is treated as end-of-file (read returns zero). Reading tables is non-blocking and non-destructive.

The element-by-element read mode is intended to enhance both forward and backward compatibility. For example, should the eproc structure be extended in the future, the extension will probably be implemented by adding new fields to the end. An application reading /dev/string/eproc element-by-element and compiled with the older smaller eproc will only read the bytes in each element that it knows about on both old and new systems.

An application built with the new larger eproc will only read the bytes which exist on the system. The unread portion of the structure should be zeroed if the application read less bytes than intended; the application should then still work on both old and new systems.

The current position in the table is set by lseek(S). Note that the current position is the offset in bytes from the start of the table; it is not the index of an element in the table.

Several ioctl(S) commands are provided (defined in <sys/tab.h>; these commands return information about the table in the argument arg to ioctl):


TAB_MIN_ELEMENT_SIZE
Returns the smallest possible size in bytes of an element.

TAB_MAX_ELEMENT_SIZE
Returns the largest possible size in bytes of an element.

TAB_ELEMENT_SIZE
If all the elements in the table are the same size, this returns the same value as both TAB_MIN_ELEMENT_SIZE and TAB_MAX_ELEMENT_SIZE. Otherwise, it fails with error [ENXIO].

TAB_TABLE_SIZE
Returns the number of elements currently in the table, or the current size of the string.

TAB_MAX_SIZE
Returns the maximum possible number of elements this table may contain, or the maximum possible size of this string.

TAB_SEEK_TO_ADDR
Returns the kernel virtual address of the start of the element containing the file offset (lseek position) arg.

TAB_ADDR_TO_SEEK
Returns the file offset of the start of the element containing kernel virtual address arg.

Tables

The following tables support both read modes:

Name in Minor number Description Structure File
/dev/table (decimal)      
proc 16 Processes proc /usr/include/sys/proc.h
pregion 17 Process regions pregion /usr/include/sys/region.h
region 18 Regions region /usr/include/sys/region.h
eproc 19 Process extensions eproc /usr/include/sys/eproc.h
file 20 Open files file /usr/include/sys/file.h
inode 21 Active i-nodes inode /usr/include/sys/inode.h
s5inode 22 S5/AFS i-node cache s5inode /usr/include/sys/fs/s5inode.h
diskinfo 24 Drive partitioning diskinfo /usr/include/sys/disk.h
dkdosinfo 25 DOS partitions dkdosinfo /usr/include/sys/disk.h
clist + 26 Character buffers cblock /usr/include/sys/tty.h
mount 28 Mounted filesystems mount /usr/include/sys/mount.h
flckrec 29 Outstanding file locks filock /usr/include/sys/flock.h
avenrun 30 Run averages scaled by 256.0 short

 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |Name in    | Minor number | Description                  | Structure | File                          |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |/dev/table | (decimal)    |                              |           |                               |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |proc       | 16           | Processes                    | proc      | /usr/include/sys/proc.h       |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |pregion    | 17           | Process regions              | pregion   | /usr/include/sys/region.h     |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |region     | 18           | Regions                      | region    | /usr/include/sys/region.h     |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |eproc      | 19           | Process extensions           | eproc     | /usr/include/sys/eproc.h      |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |file       | 20           | Open files                   | file      | /usr/include/sys/file.h       |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |inode      | 21           | Active i-nodes               | inode     | /usr/include/sys/inode.h      |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |s5inode    | 22           | S5/AFS i-node cache          | s5inode   | /usr/include/sys/fs/s5inode.h |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |diskinfo   | 24           | Drive partitioning           | diskinfo  | /usr/include/sys/disk.h       |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |dkdosinfo  | 25           | DOS partitions               | dkdosinfo | /usr/include/sys/disk.h       |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |clist      | 26           | Character buffers            | cblock    | /usr/include/sys/tty.h        |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |mount      | 28           | Mounted filesystems          | mount     | /usr/include/sys/mount.h      |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |flckrec    | 29           | Outstanding file locks       | filock    | /usr/include/sys/flock.h      |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
 |avenrun    | 30           | Run averages scaled by 256.0 | short     |                               |
 +-----------+--------------+------------------------------+-----------+-------------------------------+
+ See ``Warning'' for details of the security considerations.

The following tables also support both read modes; there is one element for each CPU:

Name in Minor number Description Structure File
/dev/table (decimal)      
sysinfo 64 System information sysinfo /usr/include/sys/sysinfo.h
minfo 65 Paging and swapping minfo /usr/include/sys/sysinfo.h
extinfo 66 Other information extinfo /usr/include/sys/sysinfo.h

 +-----------+--------------+---------------------+-----------+----------------------------+
 |Name in    | Minor number | Description         | Structure | File                       |
 +-----------+--------------+---------------------+-----------+----------------------------+
 |/dev/table | (decimal)    |                     |           |                            |
 +-----------+--------------+---------------------+-----------+----------------------------+
 |sysinfo    | 64           | System information  | sysinfo   | /usr/include/sys/sysinfo.h |
 +-----------+--------------+---------------------+-----------+----------------------------+
 |minfo      | 65           | Paging and swapping | minfo     | /usr/include/sys/sysinfo.h |
 +-----------+--------------+---------------------+-----------+----------------------------+
 |extinfo    | 66           | Other information   | extinfo   | /usr/include/sys/sysinfo.h |
 +-----------+--------------+---------------------+-----------+----------------------------+
The following tables (and all the strings) support byte-stream read mode only:

Name in Minor number Description Structure File
/dev/table (decimal)      
v 48 System configuration var /usr/include/sys/var.h
tune 49 Tunable parameters tune /usr/include/sys/tuneable.h

 +-----------+--------------+----------------------+-----------+-----------------------------+
 |Name in    | Minor number | Description          | Structure | File                        |
 +-----------+--------------+----------------------+-----------+-----------------------------+
 |/dev/table | (decimal)    |                      |           |                             |
 +-----------+--------------+----------------------+-----------+-----------------------------+
 |v          | 48           | System configuration | var       | /usr/include/sys/var.h      |
 +-----------+--------------+----------------------+-----------+-----------------------------+
 |tune       | 49           | Tunable parameters   | tune      | /usr/include/sys/tuneable.h |
 +-----------+--------------+----------------------+-----------+-----------------------------+

Diagnostics

The following codes are returned in errno on error:

[ENXIO]
The minor device number is not defined; an invalid kernel virtual address was specified with TAB_ADDR_TO_SEEK; an attempt was made to write to a string starting at a position beyond its maximum size or to read bytes starting at a position beyond the table's current size.

[ENODEV]
An attempt was made to open a read-only device for writing; an ioctl command not supported by this device was attempted (such as requesting the TAB_ELEMENT_SIZE of a string or of a table containing variable-sized elements).

[EIO]
The table is corrupted or not present in this configuration of the system.

[EINVAL]
An unknown ioctl command was attempted.

[EFAULT]
A read or write specified an invalid buffer address or size.

[EAGAIN]
The write would block and O_NONBLOCK is set for the file descriptor.

[EINTR]
The write was interrupted by a signal(S).

Warning

Table elements are usually binary data; attempting to display them directly on the terminal may result in a corrupted display or locked keyboard. Programs such as ps interpret and display elements in a safe and readable format.

The special file /dev/table/clist is not normally present as it presents a significant security risk (by making it too easy to steal sensitive information). Most devices (particularly those in the first table above) should be carefully protected. Normally they are owned by root, group mem, with permissions 440 (no access to others). This is especially important as ioctl and read are not restricted to root. If the device can be opened then it may be read and commands issued.

Authorization

Commands which use these devices should be set-GID-mem. Such commands typically should be part of the mem protected subsystem(M) so individual users can be granted or denied full or partial access.

Files


/usr/include/sys/tab.h
defines the ioctl commands listed in the ``Description''

/dev/table
directory containing the special files used by tab

/dev/string
directory containing the special files described in the string(HW) manual page

/usr/include/sys/tabconf.h
internal tab data structures and configuration definitions

/etc/conf/pack.d/tab/space.c
internal table describing each tab special file (minor device numbers less than 128 decimal are reserved and should not be used)

See also

fcntl(S), ioctl(S), lseek(S), open(S), ps(C), read(S), signal(S), string(HW), subsystem(M), w(C), whodo(C), write(S)
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003