File Attributes | Embedded Systems Firmware Demystified (With CD-ROM)

TFS supports file attributes. Each attribute (or flag) simply describes the file to TFS. An attribute in the file header is simply a bit setting. At the command line, each attribute is identified by a single letter. The following is a list of all the file attributes, including a brief description of each:

Attribute	Abbreviation	Description
executable script	e	ASCII file executed as a script
executable binary	E	binary file loaded and run based on format
autoboot	b	file is executed at startup
autoboot with query	B	file is executed at startup if user query passes
compressed	c	file is compressed
in-place-modifiable	I	file is in-place-modifiable
unreadable	u	file cannot be read at lower user level
user level	0-3	file can only be written at or above its user level

Currently, the executable binary file formats supported are AOUT (old Unix file format), COFF (common object file format), and ELF (executable and linking format). New formats can easily be incorporated into TFS.

Autobootable Files

At some point in the startup process, MicroMonitor looks to TFS for autobootable files. MicroMonitor supports three types of autobootable files: two file types designated by the attributes assigned to the file and one special case (the monrc file). For the monrc file to run automatically, it must exist and have the e attribute (executable script) set. The monrc file runs prior to any other autobootable file in TFS and prior to MicroMonitor completing its own initialization. MicroMonitor can therefore configure itself using parameters established in the monrc executable. Remaining autobootable files are run after MicroMonitor has completed initialization. The files are run in alphabetical order, so the order in which they are placed in TFS doesnt matter. The order in which they are listed via the command tfs ls is the order in which they execute.

Listing 7.1: Output of the Command tfs ls .

 Name                       Size    Location     Flags            bkgd.jpg                   5976    0x80047a6c            cardtilt.gif               6099    0x80040c1c            boot_diag                109358    0x8004921c   BE            construction.gif          20222    0x8004243c            form.html                   466    0x8004004c            my_app                   792080    0x80155a7c   BE            index.html                  442    0x8004026c            info1.html                 1053    0x8004047c            info2.html                  734    0x800408ec            lucentlogo.gif             1680    0x8004738c            monrc                        823   0x80154d2c   e

The order of autoboot execution for the files given in Listing 7.1 is:

monrc
boot_diag
my_app

All other files listed are data files used by the application. The two autobootable attributes supported are B and b , both of which run at startup. The B type queries the user at the console port, providing an opportunity to abort the autoboot of that file. If the query times out (about two seconds) before the user responds, the file executes. You can configure both scripts and binary executables with the autoboot attribute.

User Levels

MicroMonitor supports the concept of user levels. One user level is considered active at any given time. TFS supports the ability to store a file at a particular user level then limit access to that file based on the user level at the time of the access. Individual files can be marked read-only or not-even-readable. Because each user level is attainable only via password, a system can be built at user level 3 and then lowered to user level 2, 1, or 0 to provide varying degrees of protection from unauthorized access.