On Monday 02 February 2009 11:17:41 am Matthew Fleming wrote: > > In general it is far easier to just add sysinit's than to hack directly on the > > kernel linker. There are very few ddb commands, so one extra pointer or two > > per command is not a lot of space. > > Respectfully, I disagree, for several reasons. > > First, in order to make sysinit and sysctl work, the kernel linker > needed to know that there are a set of elf sections that have special > meaning. Yes, using sysinits means that there are still only two elf > sections of interest.
Yes, that is precisely the point, to keep the special knowledge in the kernel linker to a minimum. This is why kernel modules use sysinit's as well, and thus device drivers, etc. The kernel linker is already a bit complex, and I'd much prefer to keep non-linker related knowledge out of it as much as possible. > Second, as I mentioned before, having ddb commands added mixed in with > sysinits means that, if I have a bug in my sysinit I may not be able to > use some of my ddb commands to debug it. Even if DB_*COMMAND used > SI_ORDER_FIRST, any sysinit with the same priority may come first. You can still debug it, just not using your new commands. But actually, as long as your sysinit's are after SI_SUB_KLD (as most of them are), then you can still use your debugging commands just fine. > Next, if you want commands sorted globally, it could be done with either > implementation. But I think that commands that are defined by a module > should be listed with others from that module. Well, one of the "features" of ddb (IIRC) is that it allows "automatic" nicknames in that if you have a 'reallylongname' command you can just use 're' as an alias for it if 'reallylongname' is the only command that starts with 're'. Handling that basically requires a sorted list. Also, if you want to group commands in your module, that is easily accomplished by using an appropriate namespace. E.g., prior to this when I used to use 'call foo()' as a poor-man's substitute, I added commands to debug de(4) and had them all start with 'tulip_*'. You could use a similar practice to group your commands if desired. > Last, changing struct command introduces a binary compatibility issue. > Any older driver that had a ddb command (even if they never realized > they couldn't access it) would need to be recompiled. I am not sure of > FreeBSD's binary compatibility policy, though, and it would presumably > be across a major OS revision number. So this is not a very compelling > argument. Correct, it is across major OS revisions, so it is ok to change it for 8.0. -- John Baldwin _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
