On Thu, May 10, 2007 at 12:06:27PM +0200, Matthias Koenig wrote:
> There *are* of course issues with volume_id, which needs to be discussed:
> 1. udev creates label symlinks by default in /dev/disk/by-label/
> However the name of these links are not the label itself, but a safe label,
> which is derived by the rules:
> - '/' are skipped
> - multiple spaces are converted to a underscore '_'
> This will lead to problems when we have two volumes with label, e.g. say:
> foobar and
> foo/bar
> I think this is a point where blkid is smarter in detecting the ambiguity.
>
> 2. Device-by-label lookup is done by following the symlink in
> /dev/disk/by-label
> You will have to know the safe label, not the real label.
> When we want to do a label-by-device lookup, volume_id only provides
> the label (not the safe label). AFAIK volume_id does not export the
> way it derives the safe label. But this is important when we want to compare
Well, you can export the replace_untrusted_chars() function, but this
is not solution, because
replace_untrusted_chars("fooXbar") == replace_untrusted_chars("foo_bar)
if the 'X' is a unsafe character.
The concept is wrong, because you can't convert a "safe label" back
to the "raw label". The correct solution is escape (hex, oct, ...)
unsafe chars rather than remove it. So... /dev/disk/by-raw-label.
Kay?
> two labels, where the first has been given (by the user) and the second
> has been acquired by the label-by-device lookup.
> This is also a problem in the patch I have sent.
3. the symlinks in /dev/disk/by-{label,uuid} depends on udev rules.
For example /dev/loop*, /dev/dm-* and /dev/md* paths are ignored by
udev. It means you cannot mount a loop device by LABEL, ..etc.
I have talked with Kay about these things and there is also
blkid disadvantages. Kay's list:
-performance problems with huge number of block devices (tested by
SGI with 20000 or 80000 devices :-)
-doesn't detect all md signatures and returns the filesystem of a
raid-member, which is kind of dangerous
-doesn't detect the weird bios-raids, and returns the filesystem
of the raid-members
-fat is still not correct (as far as fat can be correct :))
-doesn't handle LUKS crypto
-misses hfs support (needed for iPod :))
-doesn't handle udf volume descriptors correctly
-doesn't read iso extended volume-tags correctly
-doesn't support ntfs id's
-doesn't support ufs correctly
...
I think add new filesystems to blkid is trivial.
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
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