Re: [Libcdio-devel] [Patch] More bullet-proof drive detection for GNU/Linux

[Burkhard Plaum]

Hi,

[...]
> As a back-seat driver, here are my thoughts as to why /sys or
> something like that is better. The problem with scan over a fixed
> number of device numbers is that you never can get the number right:
> either you are not scanning enough *and* on average the program is
> scanning too much.

Ok, that's right.
> We received one comment that you really can't tell what the highest
> SCSI device number would be. And right now it's set probably higher
> than what most computers in fact have. So time spent in testing for
> devices that don't exist on most computers, while still not being
> thorough.

Also agree. For each nonexistent device, we do a stat() call (called
from cdio_is_device_generic()). Don't know how much time is wasted by this.
I didn't notice a slowdown by the new method here, but must admit, that
I tested it only on pretty fast machines.

So what are the alternatives?

- opendir("/sys/block") and scan it:
  Each block device shows up as a subdirectory here (probably the best
  method if /sys/ exists).

- opendir("/dev") and scan for major numbers:
  Probably prossible for udev enabled kernels, would be awfully slow for
  pre 2.6 kernels with their 1000s of unused device nodes.

- opendir("/proc/ide"), opendir("/proc/scsi"):
  Maybe worth a try, but I don't know how reliable that is

- Talk to hald: No idea how this works (would add some dependency to libcdio)
  but "lshal | grep block.device" at least shows:

lshal version 0.4.7
  block.device = '/dev/hda1'  (string)
  block.device = '/dev/hda2'  (string)
  block.device = '/dev/hda3'  (string)
  block.device = '/dev/hda4'  (string)
  block.device = '/dev/hda'  (string)
  block.device = '/dev/cdrom'  (string)
  block.device = '/dev/cdrom'  (string)

In any case, the routines needs to try several methods.

[...]
> Recommendation such as to use strncpy over strcpy is precisely because
> the world has gotten so that you can't trust anything anymore: if
> there's a way to subvert a program someone will make use of it.

Ok, I increased the sizes of the 2 arrays by 1 and replaced all strcpy by
strncpy.

Burkhard