Comtrol eCos - Manual (Page 719)

Testing
or alternatively using some combination of --with-tcl-include , --with-tcl-lib and --with-
tcl-version .
➍ One of the host-side executables that gets built, usbchmod, needs to be installed with suid root privileges.
Although the Linux kernel makes it possible for applications to perform low-level USB operations such as
transmitting bulk packets, by default access to this functionality is restricted to programs with superuser priv-
ileges. It is undesirable to run a complex program such as usbhost with such privileges, especially since the
program contains a general-purpose Tcl interpreter. Therefore when usbhost starts up and discovers that it does
not have sufficient access to the appropriate entries in
/proc/bus/usb , it spawns an instance of usbchmod to
modify the permissions on these entries. usbchmod will only do this for a USB device "Red Hat eCos USB
test" , so installing this program suid root should not introduce any security problems.
During make install the following actions will take place:
1. usbhost will be installed in /usr/local/bin , or some other bin directory if the default location is
changed at configure-time using a --prefix= or similar option. It will be installed as the executable
usbhost_<version>, for example usbhost_current, thus allowing several releases of the USB slave package to
co-exist. For convenience a symbolic link from
usbhost to this executable will be created, so users can just
run usbhost to access the most recently-installed version.
2. usbchmod will be installed in /usr/local/libexec/ecos/io_usb_slave_ < version > . This program
should only be run by usbhost, not invoked directly, so it is not placed in the bin directory. Again the
presence of the package version in the directory name allows multiple releases of the package to co-exist.
3. A Tcl script usbhost.tcl will get installed in the same directory as usbchmod. This Tcl script is loaded
automatically by the usbhost executable.
4. A number of additional Tcl scripts, for example list.tcl will get installed alongside usbhost.tcl . These
correspond to various test cases provided as standard. If a given test case is specified on the command line
and cannot be found relative to the current directory then usbhost will search the install directory for these test
cases.
Note: Strictly speaking installing the usbhost.tcl and other Tcl scripts below the libexec directory devi-
ates from standard practice: they are architecture-independent data files so should be installed below the
share subdirectory. In practice the files are sufficiently small that there is no point in sharing them, and
keeping them below libexec simplifies the host-side software somewhat.
The usbhost should be run only when there is a suitable target attached to the USB bus and running the usbtarget
program. It will search
/proc/bus/usb/devices for an entry corresponding to this program, invoke usbchmod
if necessary to change the access rights, and then interact with usbtarget over the USB bus. usbhost should be
invoked as follows:
$ usbhost [-v|--version] [-h|--help] [-V|--verbose] < test > [ < test parameters > ]
1. The -v or --version option will display version information for usbhost including the version of the USB
slave package that was used to build the executable.
2. The -h or --help option will display usage information.
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