Letters to the Editor

Hi! I would like to thank you for doing so interesting a journal. It's my second subscription to LJ, and it won't be the last. I found the XForms review and tutorial so interesting that I decided to test it and will, perhaps, even use it at work. I enjoy reading tutorials and explanations about the Linux kernel (thanks a lot to Michael K. Johnson and all the staff of Linux Journal).

You try to spread the Linux enthusiasm everywhere. It's a success. Thank you.

Eric Bouchut

Juergen Schmidt, an attentive reader, reported a few errors in the third Kernel Korner article about device drivers, co-authored by Georg van Zezchwitz and myself. The errors are my fault, due to the limited time I had to revise the article.

The code printed within the article comes from a real driver, and it is known to run, but sometimes, I forgot to substitute the name of a symbol while copying from the real driver to the article's text.

So, Skel_Board (the structure) should read as Skel_Hw; hwp (the pointer) is equivalent to board (replace either one with the other); in skel_select, file (the struct file pointer) should read filp.

I'm sorry for these inconsistencies, and I hope they didn't cause headaches to the readers.

—Alessandro Rubini rubini@foggy.systemi.it

I have a few corrections to my article Building a Linux Firewall in LJ #24, April 1996, page 49.

1) Figure 3 is a duplicate of Figure 2. This is my fault. I submitted it this way. Obviously, cut-and-paste from one xterm to another can either be your friend or your enemy. I must have copied from the wrong window. The correct contents for the figure are shown here:

# ipfw -n list b
Type   Proto From         To             Ports
deny   udp   anywhere     192.168.1.1/32 any -> any
deny   udp   anywhere     20.2.51.105/32 any -> any
accept udp   anywhere     20.2.51.105/32 domain -> any
accept udp   20.2.61.0/24 20.2.51.105/32 any -> snmp
deny   tcp   anywhere     20.2.51.105/32 any -> any
deny   tcp   anywhere     192.168.1.1/32 any -> any

Figure 3. New blocking rule for SNMP to only accept from 20.2.61.0.

I've squeezed that down. Please use a condensed courier font to make it fit, or somehow make it a wide inline figure.

2) Several of the ipfwadm commands on page 58 have an additional character within the command line. The character is a right angle bracket, and this could cause some undesirable side effects if typed in that way.

3) The sentence on page 53 “ipfw only supports the deny and accept policies, not reject.” should be corrected to, “ipfw only supports the deny and accept policies for its output. A rule set to reject will still show up as deny.”

—Chris Kostick cykostick@csc.com

During the Space Shuttle mission STS-75, an astronaut was heard talking about the fact that Linux was installed on a computer on board the spacecraft. A few weeks later, the computer's function was disclosed. The software in use was X-based software developed under Digital Unix and ported to Linux so that it could be used on board the shuttle. Astronaut Ron Parise said in an e-mail message to fellow amateur radio operators:

Pat, et al.:

Linux was installed on one of the IBM Thinkpads that are usually flown on the shuttle. This was in support of the tether experiments. Since the ground-based applications to control those experiments ran on a DEC Alpha it was easy to just port them to a Linux system for on-board use.

73's, Ron WA4SIR