Copying Kevin because similar issues exist in the block layer. Gerd Hoffmann <kra...@redhat.com> writes:
> On Mi, 2015-06-17 at 09:50 +0200, Markus Armbruster wrote: >> Copying László because his fingerprints are on OptsVisitor. >> >> "Kővágó, Zoltán" <dirty.ice...@gmail.com> writes: >> >> > The current OptsVisitor flattens the whole structure, if there are >> > same named >> > fields under different paths (like `in' and `out' in `Audiodev'), >> > the current >> > visitor can't cope with them (for example setting >> > frequency=44100' will set the >> > in's frequency to 44100 and leave out's frequency unspecified). >> > >> > This patch fixes it, by the following changes: >> > 1) Specifying just the field name will apply to all fields that has the >> > specified name (this means it would set both in's and out's frequency to >> > 44100 in the above example). What if they have different types? What if one of them can't take the value? >> > 2) Optionally user can specify the path in the hierarchy. Names >> > are separated by >> > a dot (e.g. `in.frequency', `foo.bar.something', etc). The user need not >> > specify the whole path, only the last few components >> > (i.e. `bar.something' is >> > equivalent to `foo.bar.something' if only `foo' has a `bar' >> > field). This way >> > 1) is just a special case of this when only the last component >> > is specified. >> > 3) In case of an ambiguity (e.g >> > frequency=44100,in.frequency=8000') the longest >> > matching (the most specific) path wins (so in this example, >> > in's frequency >> > would become 8000, because `in.frequency' is more specific that >> > frequency', >> > and out's frequency would become 44100, because only >> > frequency' matches it). The current rule for multiple assignments is "last one wins". E.g. in -drive if=none,file=tmp.img,file=tmp.qcow2 file=tmp.qcow2 wins. If I understand correctly, this patch amends the rule to "last most specific one wins". Correct? >> Can you explain why the complexity is needed, i.e. why we can't just >> require full paths always? > > Keeping the short names is required for -netdev backward compatibility. I suspect mostly because NetLegacy and Netdev aren't flat unions. Could be self-inflicted pain. What about flattening them instead? Assuming that's possible; I'd have to try. > Restricting to short or full (i.e. something= or foo.bar.something=, but > disallow bar.something=) should not be a problem. I'm not sure this > simplifies things much though. We have to build the full path anyway, > and I think bar.something= is just a convenient thing we get almost for > free ... We've been bitten by convenience features before. Adding them tends to be cheap, but maintaining compatibility can become a terrible headache.