ttysrch(4)

ttysrch -- directory search list for ttymap and ttyname

Description

ttysrch is an optional file used by the ttymap(1M) administrative command. The ttymap command creates a map file, /var/tmp/ttymap, used by ttyname(3C) for fast lookups of terminal device names.

The ttysrch file lists the names of directories in /dev that contain terminal and terminal-related device files, as well as the names of directories that contain no such files. The purpose of this file is to improve the performance of ttyname by identifying subdirectories in /dev to be searched first and subdirectories to be ignored. These subdirectory names must appear on separate lines and must begin with /dev. Those path names that do not begin with /dev are ignored and a warning is sent to the console. Blank lines (lines containing only white space) and lines beginning with the comment character ``#'' are ignored. ttymap writes entries into the mapfile /var/tmp/ttymap in the order in which they occur in the ttysrch file. Subdirectories to be ignored are also specified as such in the mapfile. With the exception of /dev, entries in the ttysrch file are used recursively to identify a directory sub-tree.

When ttyname searches for device files, it tries to find a file whose major/minor device number, file system identifier, and inode number match those of the file descriptor it was given as an argument. If it does not find a match, it settles for a match of just major/minor device and file system identifier, if one can be found. However, if the file descriptor is associated with a cloned device [see clone(7)], this algorithm does not work efficiently because the inode number of the device file associated with a clonable device never matches the inode number of the file descriptor that was returned by the open of that clonable device. To help with these situations, entries can be put into the /etc/ttysrch file to improve performance when cloned devices are used as terminals on a system (for remote login, for example). However, this is useful only if the minor devices related to a cloned device are put into a subdirectory. (It is important to note that device files need not exist for cloned devices; if they do, ttyname fails.) For example, if /dev/xxxxlan is a cloned device, there could be a subdirectory /dev/xlan that contains files 0, 1, 2, . . . that correspond to the minor devices of the xxxxlan driver.

An optional second field is used in the /etc/ttysrch file to indicate the matching criteria. This field is separated from the first field by whitespace (any combination of blanks or tabs). The field is made up of a combination of the following letters:

M: major/minor device number
F: file system identifier
I: inode number
X: ignore this directory completely

If this field is not specified for an entry, the default is MFI, which means try to match on all three. For cloned devices the field should be MF, which indicates that it is not necessary to match on the inode number.

Without the /etc/ttysrch file, ttymap maps the /dev directory by first looking in the directories /dev/term, /dev/pts, and /dev/xt, and by ignoring /dev/dsk and /dev/rdsk. If a system has terminal devices installed in directories other than these, it may help performance if the ttysrch file is created and contains that list of directories.

Example

A sample /etc/ttysrch file follows:

   /dev/term       MFI
   /dev/pts        MFI
   /dev/xt         MFI
   /dev/slan       MF
   /dev/dsk        X
   /dev/rdsk       X

This file tells ttyname that it should first search through those directories listed, that when searching through the /dev/slan directory, if a file is encountered whose major/minor devices and file system identifier match those of the file descriptor argument to ttyname, this device name should be considered a match, and that neither /dev/dsk nor /dev/rdsk need be searched.

Files

/etc/ttysrch

References

clone(7), ttymap(1M), ttyname(3C)