1ELEKTRA(5) ELEKTRA(5)
2
6 elektra - A framework to store configuration atoms hierarchically
7 Note
9 This section is provided for the sake of the openness of Elektra. You
10 should not access the Elektra´s key files directly. You should use the
11 API or the kdb(1) command for that.
12 Elektra Key Storage Strategy.PP Elektra implements a very simple way to
14 store the key-value pairs. The value (and some metainfo) for each key
15 is stored in a single file. The key name (and some of its context) is
16 sufficient to find the file name that stores the value.
17 The system/* keys are stored under /etc/kdb/, and the user/* keys can
19 be found under each user´s $HOME/.kdb/.
20 Here are some examples of key names, and where Elektra goes to look for
22 them in the disk.
23 system/sw/XFree86/screen0/driver
25 Maps to: /etc/kdb/system/sw/XFree86/screen0/driver
26 user/env/PATH
28 Maps to: ~$USER/.kdb/user/env/PATH
29 user:luciana/env/PATH
31 Maps to: ~luciana/.kdb/user/env/PATH
32 system/mime.types/some.mime
34 Maps to: /etc/kdb/system/mime.types/some.mime
35 Some may think that one file per key will consume many filesystem
37 i-nodes. Actually, when not using Reiser4 filesystem, it may consume
38 some more disk space, and it may also be not so efficient than reading
39 one single text file, as KConfig does. But Elektra´s nature lets
40 applications load their keys on demand; so it is possible to avoid the
41 read-all-use-some approach. Writing updated keys back to disk is also
42 more robust, because unchanged keys won´t be touched, different from a
43 single file approach, that must be entirelly rewritten.
44 Besides that, big applications (like Mozilla, Konqueror, KDE, Gnome)
46 key gathering time is a very small part of what they have to do to
47 start up. And the benefits of an homogeneous key database to the entire
48 system are much bigger then these issues. Think about a common
49 integration between everything, flexibility, security granularity and
50 openness. XML, Storage Backends and Elektra.PP This document you are
51 just reading was written in DocBook XML. XML is a wonderfull
52 technology, but brings no value to this software. Two main goals of the
53 Elektra Project are to be lightweight, and to be accessible by early
54 boot stage programs like /sbin/init and the /etc/rc.d scripts.
55 XML parsing libraries are memory eaters, not so fast as we can expect,
57 and they are usualy located under /usr/lib, which may be unavailable to
58 these early boot stage needs.
59 Some discussions asked for a sort of plugin architecture to let user
61 decide the format to store keys content. Well, the info that goes into
62 the key file is not big deal as you´ll see, and sometimes, too many
63 options is bad business, and not the path for the Elektra Project.
64 So no XML, no plugin architecture, no sophistication. Lets keep it
66 simple and generic. A very straight forward text based file format was
67 defined to store a single key value. Key Files Format.PP Inside
68 Elektra key database, each key is a file, and every file is a key. So
69 most of the key´s metainformation are actually its file attributes, as
70 you can see in a regular ls(1) command output.
71 So what needs to be stored inside the key file is the data type (binary
73 or text), key comment and the actual data. The format of each key file
74 is:
75 File Format Version
77 Data Type
78 As many lines of
79 comments as we want (UTF-8 encoded)
80 <DATA>
81 The data encoded as text
82 So if we set the key system/hw/eth0/driver as type String and value
85 "3com", and comment "The driver for my network interface", we´ll find
86 the file /etc/kdb/system/hw/eth0/driver containing:
87 RG002
89 40
90 The driver for my network interface
91 <DATA>
92 3com
93 Other example: setting user/tmp/proprietary as Binary, and value "A
96 groovy data I want to hide", and comment "Stay away from here", you´ll
97 get in ~$USER/.kdb/user/tmp/proprietary the following:
98 RG002
100 20
101 Stay away from here
102 <DATA>
103 41206772 6f6f7679 20646174 61204920 77616e74 20746f20 68696465
104 The current data types are:
107 Between 20 and 39
109 Binary value. The data will be encoded into a text format. Today
110 only type 20 is used, and means a raw stream of bytes with no
111 special semantics to Elektra. The other values are reserved for
112 future use; being treated still as binary values but possibly with
113 some semantics to Elektra or a higher level application.
114 40 up to 254
116 Text, UTF-8 encoded. Values higher then 40 are reserved for future
117 or application specific implementations of more abstract data
118 types, like time/date, color, font, etc. But always represented as
119 pure text that can be edited in any text editor like vi(1).
120 Types between 0 and 19 are used only internaly in the API, and will
122 never appear into a key file. They are used to define meta keys as
123 directory, link, etc.
124
126 kdb(1), elektra(7)
127
129 Avi Alkalay <avi at unix.sh>
130 Linux Market Developer, Senior IT and Software Architect, IBM Linux
131 Impact Team :: ibm.com/linux
132 Author.
133
135 Copyright © 2004 Avi Alkalay
136Elektra Initiative March 2004 ELEKTRA(5)