isdninfo - ISDN status device
/dev/isdninfo is a character device with major number 45
and minor number 255. It delivers status information from
the Linux ISDN subsystem to user level.
When reading from this device, the current status of the
Linux ISDN subsystem is delivered in 6 lines of text. Each
line starts with a tag string followed by a colon and
whitespace. After that the status values are appended sep
arated by whitespace.
idmap is the tag of the first line. In this line for
every virtual channel, the Id-string of the corre
sponding lowlevel driver is shown. If no driver is
loaded, a - (hyphen) is shown.
chmap is the tag of line 2. In this line for every vir
tual channel, the channel number of the correspond
ing lowlevel driver is shown. If no driver is
loaded, -1 is shown.
drmap is the tag of line 3. In this line for every vir
tual channel, the index number of the corresponding
lowlevel driver is shown. If no driver is loaded,
-1 is shown.
usage is the tag of line 4. In this line for every vir
tual channel, the current usage is shown. The fol
lowing usage constants are defined:
Channel used by raw device (currently unsup
Channel used by some ttyI
Channel used by an ISDN net-interface
Channel used by some ttyI in voice mode.
Channel exclusively preserved for a net-
interface. This value is logically or'ed
with one of the other codes.
Channel is used outgoing. This value is log
ically or'ed with one of the other codes. It
is set, when dialling is started and reset,
when either dialling failed or after hangup.
Therefore, it is not always an indicator for
an established connection. To get a reliable
indicator for an established connection, the
driver flags (see below) have to be
flags is the tag of line 5. In this line for every driver
slot, it's B-Channel status is shown. If no driver
is registered in a slot, a ? is shown. For every
established B-Channel of the driver, a bit is set
in the shown value. The driver's first channel is
mapped to bit 0, the second channel to bit 1 and so
phone is the tag of line 6. In this line for every vir
tual channel, the remote phone number is shown if
the channel is active. A ??? is shown, if the chan
nel is inactive.
After opening the device, at most 6 lines can be read by a
user process. After that, the user process is blocked.
Whenever a status change happens, the process is allowed
to read 6 more lines, starting with line one.
Currently, there are two ioctl calls supported:
Get Revision information.
Returns an unsigned long value v, representing var
ious user level interface revisions, where
(v & 0xff)
is the revision of the modem-register info,
available via ioctl on /dev/isdnctrl.
((v >> 8) & 0xff)
is the revision of the net-interface config
data, available via ioctl on /dev/isdnctrl.
is the revision of the data delivered via
Get transfer statistics.
Returns the number of bytes transferred so far for
all virtual channels. The third parameter should be
a pointer to an array of unsigned long of size
ISDN_MAX_CHANNELS * 2. This array is filled with
the byte counter values upon return.
There are some more useful constants defined in
The major device number of /dev/ttyI.
The major device number of /dev/cui.
The major device number of /dev/isdnctrl, /dev/isd
ninfo, /dev/ippp and /dev/isdn
The number of driver slots.
The number of virtual channels.
The minor device number of /dev/isdnctrl0.
The minor device number of /dev/isdnctrl63.
The minor device number of /dev/ippp0.
The minor device number of /dev/ippp64.
The minor device number of /dev/isdninfo.
Other constants, necessary for ioctl's on /dev/isdnctrl
are listed in isdnctrl(4).
Fritz Elfert <firstname.lastname@example.org>