Wandering Thoughts archives

2008-07-18

One consequence of Linux's dynamic network device naming

I knew that Linux did dynamic network device naming, but one consequence of that only really sunk in recently. Dynamic naming is relatively predictable for interfaces that are always on (especially when various distributions work hard to make them very persistent), but where it can really surprise you (and your software) is when the interfaces are dynamic. Like, say, PPP interfaces.

Just like Ethernet interfaces, the first active PPP connection gets ppp0, the second one gets ppp1, and so on. But unlike Ethernets, PPP connections can routinely come and go, and as a result it may not be clear to you (or your software) what PPP device is what connection. Also, it is easier to commit the old mistake of trying to bring up a connection that's configured as ppp1 when you don't have a ppp0.

(Scripts run by pppd itself get told the right network device, which can be both useful and potentially confusing.)

Unfortunately it looks like you cannot rename PPP devices, because it seems that you can only rename network devices that aren't active and when a PPP device isn't active, it doesn't exist at all. So I can't have pppdialup0 and pppdsl0 instead of, well, whatever pppN name they get right now.

One can half-fix this with software; pppd has a concept of a logical link name, and contrary to what the manual page appears to claim, it does pass this information to the ip-up script as the environment variable $LINKNAME. So your local link-up script can save the mapping between actual PPP device (the first argument) and the logical link name somewhere, and then other things can read it.

linux/PppConnectionNaming written at 23:57:33; Add Comment

The advantage of blog comments

The advantage of having blog comments is that they are the easiest way for people to, well, make a comment on an entry. The main alternative is email, but blog comments are significantly easier than email in this modern age of spam and other problems, where not only is it difficult to find the blog author's email address (because if it was easy to find the spammers would find it), but it's difficult to know if you can trust them with your email address.

(While writing an entry of your own can be easy, my feeling is that it's not an effective way of commenting because there's no good automatic way of bringing it to the attention of the original author. In theory trackback would solve this problem, but in practice it has drowned in spam.)

When you make things more difficult, fewer people care to go through the effort, especially first time people, and as a result you'll get fewer comments. Mind you, sometimes this is a desirable state of affairs; there are drawbacks to comments, especially a lot of comments, and that's ignoring the entire issue of comment spam.

(Note that someone who 'comments' regularly has less problems; they will know your email address or other way of getting your attention (or not care), they will have already decided to trust you with their email address, and so on.)

It is my guess that you will not necessarily get a better class of comments by making commenting harder; you may even get a worse one overall. The problem is that you're not selecting for people who have something good to say, you're selecting for people who care enough, including people who have a pet cause that they will only be too happy to tell you about. (On the other hand, it is generally easier to filter such people out of email and other ways of attracting your attention than it is to filter out their blog comments, and this effect may not kick in until you are fairly well known.)

(Obligatory attribution darnit: this entry was inspired by this, which started me thinking about the general issue.)

web/CommentsAdvantage written at 00:36:07; Add Comment


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