Re: union mounts not supported?
Re: union mounts not supported?
- Subject: Re: union mounts not supported?
- From: Dan Shoop <email@hidden>
- Date: Tue, 2 Nov 2010 15:33:16 -0400
On Nov 2, 2010, at 7:12 AM, Quinn The Eskimo! wrote:
>
> On 1 Nov 2010, at 21:36, Dan Shoop wrote:
>
>> This sounds like it's describing the former union mount rather than the latter unionfs and sounds as if it's saying the "-o union" isn't supported, but you claim it is (and empirically it appears to be as well.)
>
> I think we're talking at cross purposes with regards the definition of "supported". In my case I mean "supported as a long-term binary compatible interface to the system". Under that definition you can't empirically test whether something is supported or not. It sounds like you're using the term "supported" to mean "implemented", which is something entirely different (-:
I understand both cases of "supported" with regard to implementation.
The hdiutil man page specifically says that the -union option is just a no-op. I inferred that this meant "not implemented". I took this also to read that it was referring to union mounts, the "-o union" thingie.
Shantonu brought up unionfs, which I hadn't read into that at all, and that unionfs was entirely unsupported.
So I had taken away from Shantonu that it's unionfs that's was what's no longer supported/implemented and referred to by the hdiutil man page.
But now sounds like it meant that since the level of "support" was depreciated that the function of built in union mounting that previously existed in hdiutil was replaced with a no-op if you attached a disk image to a mountpoint and wanted it to union mount against the hierarchy underneath that mountpoint.
So while I'm left slightly perplexed as to which the hdiutil man page specifically referred to as now being "unsupported" you've both afforded me an understanding of what to expect relating to each. unionfs totally unsupported and unavailable; union mounts don't count on. In either case -union on `hdiutil attach` is now a no-op.
Of course the possible disappearance you suggest of the union option in mount would be most disappointing as it is useful, despite the caveats, much as shadow files are with disk images. It's level of "support" so long as it's implemented, withstanding.
If OS X engineering's stance is that the union mount option maybe going away and in any case shouldn't be used or counted on in OS X then this is sad.
Again, thanks for the responses.
-d
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Dan Shoop
email@hidden
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