Bloggy

In the spirit of my series of programming tips articles I thought I would go ahead and throw out some more:

• If you are using QAction, QCheckBox, QRadioButton, or similar classes, then you need to be wary of the differences between the toggled(bool) signal and the triggered(bool) (for QAction) or clicked(bool) (for button-like classes) signals.

  These two signals are used in two different situations. toggled(bool) is always for if the value of the action or button being checked changes, for any reason. This means that if an QRadioButton had not been checked, and it is set to being checked, it will then emit a toggled(true). You would use this signal if you needed to update your GUI based on whether an action is checked for instance.

  The other signal (triggered or clicked) are used when you need to perform an action based on a user action. For instance, if you had a "[ ] Show Wikipedia content" on your menu bar, you may want to bring up that window as soon as the user clicks on it. On the other hand, if you were changing the checked status of the action internally to your code but didn’t want the window to pop up, you’d want to use the triggered signal.

• If you’re not continuing to study then you’re not going to get any better at programming. I’ll generally visit programming.reddit.com (and also the C++ and Perl sub-reddits) and sometimes you’ll catch a new technique that is neat. For instance:
• From Mr. Edd’s C++ blog: You can use the not-well-known feature of C++ to give “pointers to member data” to allow for assigning a null pointer to smart pointer classes, while not allowing any other pointers to be assigned. His writeup covers everything so I’ll refer you to that but suffice to say that something like “smart_ptr service = 0 would work, while “smart_ptr service = &newService” would not. This is useful in basically any place where you want to allow a null pointer to be assigned by not any other kind of pointer.
• Another interesting tidbit is the restrict keyword, available in C since the C99 revision. Sadly, it is not available in C++, not even the upcoming C++0x standard, except as a compiler extension. The use of the keyword is fairly low-level, and is explained in this article for Cell processor development.

Hopefully you’ve learned something neat (and useful and not merely contrived!)

Posted by mpyne under C++ & Programming & Useful Tricks | 1 Comment »

I’m sure there’s already a million “Happy New Year” type posts up but I figured I’d throw in my two cents as well (since I’m actually here for this New Year’s Day).

While I’m at it I’ll pass along some things I managed to accomplish over the past week:

• Have some troubleshooting that you need to do that requires you to have a small partition? (In my case, troubleshooting for bug 118594). You don’t need to re-format your hard drive. Instead (at least on Linux) just create a partition on a file:
  1. Create a small-ish file (for instance, using dd if=/dev/zero of=file-name-here bs=1M count=size-in-megabytes).
  2. From there, you need to create a filesystem on it. I used plain ext2. If you’re not running as root you may need to manually run /sbin/mke2fs file-name-here. (since /sbin is normally only in the PATH for root). mke2fs should complain about the file not being a special block device but you can tell it to proceed. Please note that mke2fs is a horribly horribly destructive thing to do on a live filesystem. Make sure to take the extra second to get the filename right, and don’t run mke2fs as root.
  3. From there you can mount the file using the loop device. I had to do the following: mkdir test-dir # Create directory to mount filesystem to
sudo mount -o loop ./file-name-here ./test-dir/.
     On my system root permission is required to run mount even for a single-user mount like this, it may be different on yours.
  4. Now use your new filesystem normally. Any changes that you make to the test-dir/ folder actually affect the file you created for that purpose. This is handy for testing out-of-disk-space problems in your app.
• If you use Gentoo you will want to start shifting over to split ebuilds if you haven’t already. Their KDE-style modules were stopped (for the most part) at KDE 3.5.9, which was fine with me until every emerge world I tried to run started complaining about blocked packages at the various kdelibs requirements started to get inconsistent. I’ve decided to take this opportunity to simply get rid of the majority of the system KDE 3 and upgrade to KDE 4.1.3 instead. So far my wife hasn’t complained about it at all (and she really likes KSudoku as well) so as soon as I’m convinced I haven’t forgotten to install a KDE 4 program I’ll need I’m going to uninstall KDE 3 with the exception of the libraries and a few apps.
• World of Goo is definitely worthy of play. A Linux version is in beta but the Windows demo ran fine for me in WINE. Well, it crashed WINE on shutdown before the video mode had been restored but I suppose that’s good enough nowadays. :)

Posted by mpyne under Computing Troubles & KDE & Personal & Useful Tricks | 1 Comment »

I’m not sure when this changed in KDE 4 but if you move your mouse to the upper-left corner and keep trying to “push” you’ll get the “exposé” effect without having to use the keyboard shortcut, and then click on the window you want. Handy alternative to Alt-Tab.

Posted by mpyne under KDE & Useful Tricks | 12 Comments »

So before I went underway our car had developed a trouble causing the Check Engine light to come in continuously. No abnormal sounds but being nuclear-trained has taught me not to live with “locked-in” alarms or warnings. I wasn’t able to troubleshoot it in the limited time I had before deploying so I asked my wife to make sure it got investigated when she had free time.

She took the car to the dealership. She actually had to make two trips; apparently there were two separate faults that would have caused the light to come in by this time. Nothing mechanical luckily, but apparently at some point while the dealership was troubleshooting the issue they had to unhook the battery. Doing this activated the anti-theft feature of my radio; it would not play music unless I typed in the anti-theft code. This code was included on a card which I was supposed to remove from the car and keep in a safe place. Needless to say, I had removed it from the car, and it is still in some safe place, nowhere to be found.

So my car radio has been silent for about a month and a half now. I finally got the time to really dig into this issue since the dealership apparently is completely unable to figure out what the unlock code should be. A little browsing on the Internet and apparently many people have had the same issue, and the unlock codes are few enough to list in one paragraph.

So I went and wrote them down and typed them in one by one. After about a dozen tries the radio started working again. Yay! I will record the code in my KWallet this time; it is the only thing which I reliably can count on being there. In case anyone else develops this issue with a Chevy Aveo, I found these posts helpful: automotive forums and Yahoo! Answers.

Posted by mpyne under Personal & Useful Tricks | 3 Comments »

kio_perldoc: I’ll keep it short:

• Ported to KDE 4.
• The GENERATOR metainfo in the output has kio_perldoc now, so that proper blame may be placed.
• The S<> tag in Pod now produces HTML which isn’t super broken. (Look for Mac OS in perlport)
• Don’t try to load IMG tags. I wasn’t going to add this in except that it causes Konq 4 to crash for some reason.
• Fix formatting of bulleted lists. Patch graciously provided by Bruce Ravel.
• All C library functions are called like ::foo() now to avoid ambiguity. (e.g. with close())
• Corrected a call to execlp(). If you ran kdeinit in a terminal you could actually see the man page come up…
• Fix linkage for hyperlinks that refer to the same page.
• The HTML output looks more like www.kde.org now.

Still needs CMake, Perl 5.8, etc. The KDE 3 version is 0.8.1, and KDE 4 version is 0.9, but it’s the same feature set.

Posted by mpyne under KDE & Programming & Useful Tricks | 1 Comment »

All that work I was doing to add parallel updating and building to kdesvn-build gave me a great appreciation for one thing that Perl does right: copious documentation, even if you need to use a special program to view it (perldoc, which man-page-ifies it).

What I really wanted was a KIOSlave interface to perldoc that way I could view the documentation nicely hyperlinked in Konqueror. The KDevelop guys already had a kio_perldoc, but it wasn’t really too great. It simply dumped the output of perldoc more or less straight to konqueror, which misrendered it since it wasn’t HTML. It could also output plain text but that was HTML-ified using blockquote instead of pre which caused it to still look weird.

It was that way mainly because there’s no good way to export HTML from a perldoc file. Perl includes a pod2html but let’s just say it hasn’t kept up with the times too well. Plus it’s very hard to convert the hyperlinks produced by pod2html into something that perldoc would be able to redirect to itself, which defeated the purpose of having hyperlinks in the first place.

I eventually decided to do a little Perl magic to handle the conversion from .pod (which perldoc would output) to html that wasn’t crap. It took a bit of searching on CPAN to weed out the POD->HTML converters which either had way too many dependencies or didn’t produce suitable output. I eventually settled on Pod::HtmlEasy, a useful and customizable Pod->HTML converter that didn’t have too many dependencies and was suitable for standalone use.

Some merging of files and removal of unnecessary dependencies later, and I had a script which would run perldoc for me and automatically convert its output to HTML. All my KIOSlave had to do was call the script and dump its output straight to the receiving end.

The actual handling of that is probably more complicated than necessary. I think I will use popen() in the future just like every other similar KIOSlave instead of handling the children myself. But, it works pretty well:

It handles URIs of the form perldoc:/Net::HTTP to get module information, perldoc:/functions/select to look up documentation on Perl functions (like perldoc -f) and perldoc:/faq/search_terms to looks for your search terms in the perlfaqs (like perldoc -q). These URIs were all pioneered by the KDevelop KIOSlave.

The next step would probably be to port this to KDE 4 and coordinate with the KDevelop developers to either integrate this back into KDevelop or (my preference) get this into kdesdk since this is useful for many more developers than just KDevelop users. Also the generated HTML looks very similar to perl.org’s perldoc resources, I need to get it looking more like the kde.org website family (CSS help appreciated :)

You can grab it from my dumping ground. Although it is for KDE 3, you still need CMake to build it, as there’s no way I’m wasting bandwidth on autotools. :)

Posted by mpyne under KDE & Programming & Useful Tricks | 5 Comments »

I’ve started on work to implement a feature requested in bug 109619. Namely, to allow kdesvn-build to start the build process as soon as the first module has been updated from subversion and then to run the two updates in parallel as much as possible.

It’s harder to do than it sounds at first but I think I have something working. If you try it out (latest kdesvn-build from trunk/KDE/kdesdk/scripts) and it’s broken for you please let me know.

Also some KMail/Kontact tips for you: I don’t know why but I was under the impression that the “Mark Thread As->” feature required you to click on the root email of the thread in question. That’s not the case, any message in the thread will cause the whole thread to have the desired attribute applied. Also, if you ever get messages in your inbox that simply refuse to go away then you may have a bad message folder cache. At least for Maildir type accounts. In that case, shut down Kontact and KMail (including from the system tray), go to your Maildir folder (mine was ~/Mail) and look for hidden files of the type .folderName.index* (I had .inbox.index, .inbox.index.ids, and .inbox.index.sorted in mine).

RENAME these files to something else (I moved them to a backup directory), and then restart Kontact. It may take a couple of seconds to rescan your folder (although it was near instantaneous on my system) and then you should have your folder corrected with all the undeletable messages gone.

Posted by mpyne under KDE & kdesvn-build & Useful Tricks | 4 Comments »

Update 2009-10-10: Updated link to software

So after having a Gentoo upgrade break a lot of programs, even after running the revdep-rebuild which rebuilds packages affected by a changed library, I decided that I had to have a way to find out what libraries in particular were causing programs to need to load the affected library. In my case an expat upgrade replaced libexpat.so.0 with libexpat.so.1. Even though revdep-rebuild was supposed to rebuild the affected packages it missed quite a few.

(I would eventually figure out that the reason it messed up is because the lib64 directory is symlinked to lib since I have a 64-bit system. The program would end up linked against a library in /usr/lib64, revdep-rebuild would look for programs linked against the exact same library, but in /usr/lib instead, and then not find it.)

Anyways, after playing around with ldd and discovering that it would not give a nice tree diagram showing what the dependencies of a program was I decided to make a tool that would do so. I call it ELF Library Viewer (elflibviewer on the command line):

If it interests you at all it is available from my software page. It requires Qt 4 and the readelf utility to be installed. It doesn’t really do much error handling (i.e. run it on ELF executables and libraries and you’ll be fine) but it shouldn’t ruin your binaries either.

It is rather Linux-specific at this point as well, but it should mirror the GNU binutils way of finding libraries closely. Instead of searching the ld.so cache it checks ld.so.conf to figure out what ld.so should be caching however. Let me know if this program proves useful for you (or if I’m just reinventing the wheel). Bonus tip: Type the name of the offending library into the search line and hit enter. It will highlight in red all of the libraries which depend on the offending library. It also recursively resolves dependencies, but only the first time it sees a library. It probably wouldn’t be too hard to copy over the dependency tree each time it reencounters a library but I can’t be bothered to implement it.

Posted by mpyne under Computing Troubles & KDE & Screenshots & Useful Tricks | 17 Comments »

In the past couple of hours I’ve managed to fix 3 different screwups I made with qmail. Because having to deal with qmail (or rather, MTAs in general) always gets me upset, I figured I’d document what I’ve done for posterity. Sorry to the Planet KDE readers, this is longer than I thought it would be.

For starters, when you setup qmail, don’t forget to add all the aliases for your machine to the /var/qmail/control/locals file. No, qmail doesn’t know that localhost is actually a local machine, nor does it automatically know about your computer name. So in my case, I’d forgot to add midna (the computer name) and localhost to the locals file before email was being sent, and although qmail retained it, it was trapped in the queue, unable to be delivered.

qmail splits up its queue into two sections, remote (which it tries to deliver over SMTP) and local (which it normally can just deliver to on disk). In my case qmail is pretty much receive-only, so SMTP-outbound delivery wasn’t working (and wasn’t likely to¹). And anyways, all the crap stuck in the remote queue really belongs in the local queue, and it would have been there if I hadn’t screwed up the locals file.

Now the QMail queue is a very touchy part of the filesystem. Try moving files around and you’ll likely hose all the email retained in there, not to mention any email delivered to qmail in the future. So it’s not like you can just move messages from the remote to the local queue. Instead, what you should to when you’ve got messages in the remote queue that need delivered locally, is to play with the /var/qmail/control/smtproutes file. This file controls the SMTP servers which are used to relay messages.

Something like this will tell QMail that messages intended for your local domain should be SMTP’ed out to localhost. QMail will receive them and, since your locals file is now correct will put them in the local queue where they’ll be delivered.

localhost.localdomain:[127.0.0.1]

That takes care of the first problem. But, don’t forget to remove the entry again after the mail has been placed in the local queue! Another problem I was having was that emails to an old user of mine weren’t being delivered to the correct email account. qmail has nifty support for address of the type user-foo@domain, where the -foo part can be whatever user wants, which is nice for getting unique email address to give to merchants or other websites you suspect may give away your address. It’s even useful simply for filtering (which is what I was using this particular address for).

Now qmail also has a nifty aliasing feature that allows messages sent to a virtual user to be redirected to a mailbox. All you do is create a .qmail-user file in /var/qmail/alias, the contents of which is the name of the mailbox to send to (i.e. mpyne).

But, this has two problems. First, email sent to user-foo won’t be redirected. If you want that to happen you need to name the alias file .qmail-user-foo. This would get unwieldy (imagine all the possible suffixes you could have added). But, if you have a .qmail-user-default alias, then any email which doesn’t match a different alias for the user will be redirected to that alias. So that solved my second problem.

The final problem is that the alias feature doesn’t work if you’re trying to alias email for a user that has an account on the system. In my case, I was having email sent to portage@midna forwarded to my account. But, portage is an actual user account on Gentoo systems. So even though the alias existed, qmail was searching for portage in /etc/passwd first, and found the entry. qmail in this situation then checks to see if the user owns their home directory, that the permissions are set right, etc. That wasn’t true in this case, so email sent to portage was in limbo.

The solution here is to take advantage of a QMail users database. By default in /var/qmail/users. You need to read the man page for qmail-users, but basically you setup the file /var/qmail/users/assign to redirect email for the user to someone else, run the qmail-newu program, and then the user database which is created is checked first, before checking for the home directory. And if the user isn’t present in the database then the rest of the sequence goes on unchanged so this won’t break your aliases and existing mailboxes².

My disclaimer is that this is all probably completely different if you’re using software like vpopmail or other user administration software bolted on top of qmail. My particular scenario was a qmail-only install. You may want to have the qmHandle program or similar available to help manage messages in your queue. And, be vary wary with any queue changes while qmail is still running. pkill -HUP qmail-send is your friend when changing files in /var/qmail/control. Sometimes restarting qmail is in order as well.

[1]: Strictly speaking it’s probably poor form to be able to receive SMTP messages without the capability to send a bounce back to the originator. So I’ll rig it to have outbound send capability before too long.
[2]: At least, I don’t think it will.

Posted by mpyne under Computing Troubles & Useful Tricks | 3 Comments »

I’m tired of looking up information on how to use those special fancy features to do parameter substitution in bash scripts, so I’ve decided to blog about it (at least some of the more useful ones). It’ll be quicker to find it this way than to Google it again.

First off, let me demonstrate with a sample:

KDEDOCS=${KDEDOCS:-default}

The :- says that if KDEDOCS is unset (or is set to a null value), then to use default as the result. The original variable is left unchanged.

There are other useful ones, which I’ll summarize here. For more definitive information, consult the Advanced Bash Scripting Parameter Substitution page, which is where I found the explanations. Also, as you may guess from the page title, some of these substitutions are specific to the bash shell. The example I gave seems to work on plain sh compatible shells though, but I can’t check.

Apparently the following options were taken from ksh. So, you can assume that they’re not plain sh compatible:

So, intrepid bash hackers, put these tips to good use!

Posted by mpyne under Programming & Useful Tricks | 1 Comment »