z 1998-08-09 Emil Brink gentoo FileTypes INTRODUCTION This document describes the gentoo filetyping architecture, i.e. the means by which gentoo clasfsifies each file it shows as belonging to exactly one previously defined file type. This classification is then used to determine how gentoo is to deal with that file; it helps specifying display colors and/or pixmaps, action commands, and so on. In this document, the word "file" is used in a very general sense. A file is anything that can be found in a disk directory. Since gentoo runs on Linux (and perhaps other Unices?), this means that a file can be a directory, a plain file, a (soft) link, a (block or character) device, a socket, or a FIFO. At least I _think_ that's all... THE FILETYPE A filetype is, technically, a named tuple of identification methods. These methods can be applied to a dirpane line to determine if the disk entry described by the line belongs to the type or not. A filetype can use anything from one to four available "levels" of identification methods in order to determine if a given line has the type. These levels are: 1) inode type This is the simplest, fastest, most low-level check. The inode type tells if the line is a directory, a soft link, plain file, device, et cetera. A filetype MUST ALWAYS specify exactly ONE inode type. 2) Protection Using the protection matching rule, you can require files to have a certain combination of protection bits. You can currently only specify which bits must be set, not which must NOT be set (i.e. clear). This means that you can find all files that are writable, but not all files that are NOT writable... I don't know how important this really is, but it feels kind'a incomplete right now. 3) Suffix Match The suffix match is used to require that the file name ends in a certain string. This is very useful to find normal extensions, since a typical extension is just a suffix with a dot first. For example, you could use the suffix match to require that candidate lines have names ending in ".gif". This check is highly specialized and therefore fairly quick. Since the suffix checker is meant to be lean, mean and quick, it only allows one suffix rather than a list. If you need to check against several suffixes (suffici? suffixen?), you'll need to move to the next leve, the regular expression matcher. 4) Name Regular Expression Match If the names you're trying to find have some similarity more complex than just a plain suffix, maybe you can use this level. It lets you specify a full regular expression (using the V8 syntax found elsewhere in gentoo) against which file names are checked. For example, if you where looking for MOD files on an Amiga partition, you might specify a name RE of "^mod\..*". Or you could identify tar+gzipped files with "(\.tar\.gz$)|(\.tgz$)". 5) 'file' Regular Expression Match When none of the previous levels suffice, you can resort to the final secret weapon; the 'file' regular expression matcher. This runs the UNIX standard utility 'file' on the dirpane line in question, and then tries to match the regular expression you supplied against file's output. Using this level, you can perform virtually any kind of file identification necessary, since you can add things to the "magic" file /etc/magic used by file. As an example, you can identify executable files in the ELF format (standard on modern Linuxes) by specifying a 'file' matching RE of e.g. "ELF 32-bit (L|M)SB executable.*", or just plain "ELF.*". Note that the RE you specify is only checked against the part of file's output that is after the first colon. Please remember that using 'file' RE matching in your file typing SEVERLY degrades gentoo's performance. Beware. I'm waiting for a new release of the 'file' package that incorporates a tiny fix which will allow gentoo to use it with much greater efficiency... FILETYPING STRUCTURE Gentoo maintains a set (e.g. a list) of filetype definitions; there is no hierarchy or any other complex structure involved. The definitions are applied one by one in search for a match. As soon as any a match is found, the search is terminated and the line as considered to have the type that matched. If no type matched, the built-in always present type "Unknown" is assigned to the line, in order to guarantee that all dirpane lines always have exactly one type assigned to them. The ordering of the filetypes internally influences the speed of the matching process; this is something I will investigate once the filetyping has been more fully implemented and is somewhat stable. STYLES A filetype is just a way of specifying how to identify files that have things in common. Once the files have been partitioned into groups by their file types, it would be nice to take advantage of this grouping when working with the files. This is done through the use of styles. A style contains information that gentoo uses when rendering the dirpane; colors and pixmaps for example. It also holds data used when you manipulate the file (double-clicking it, or trying to view it with the built-in View command). Styles, unlike filetypes, form a tree structure. There is a single, always-present, "root" style. Other styles then appear as either internal or leaf nodes in the tree based in the root style. STYLE PROPERTIES The following properties can be specified in a style: DISPLAY Unselected Background Color Foreground Color Pixmap Icon Selected Background Color Foreground Color Pixmap Icon ACTION Double-click View Edit Print Play PROPERTY INHERITANCE The reason why the styles are arranged into a tree structure is to facilitate inheritance of properties. For each style (except the root) you specify which properties are to be changed from the ones of the parent style. Those that are not changed are then taken from the parent, recursively. The root style always specifies all its properties. If you're into C++ and object-oriented programming in general, this should be right up your alley.
