October 2008 - Darwin-kernel

Re: Hard links to directories
by Mike Tegtmeyer 03 Oct '08

03 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com My .02, Mike On Oct 2, 2008, at 8:50 PM, Chris Idou wrote: --- On Thu, 10/2/08, Kevin Elliott <kelliott(a)mac.com> wrote: From: Kevin Elliott <kelliott(a)mac.com> Subject: Re: Hard links to directories To: idou747(a)yahoo.com Cc: darwin-kernel(a)lists.apple.com Date: Thursday, October 2, 2008, 3:32 PM On Oct 1, 2008, at 8:00 PM, Chris Idou wrote: > > A couple more questions: > > 1) How do permissions work? I notice that the system seems to stop > you doing dangerous things like hardlinking /System to somewhere, > even as root, but its not clear why this case is different. Can't shed any light on that. As someone else has mentioned, directory hard links should effectively be considered SPI. If you want help understanding them so you can work better with TimeMachine, that's great. If you think you can use them to solve some other unrelated problem, then your making a mistake and should reconsider what your trying to do. > 2) I notice that once a directory has been hardlinked, it is forever > tainted in some fashion. If I hardlink a directory somewhere, then > unlink the 2nd link, then the original directory can never be > trashed in the Finder for example. Such an attempt will fail, even > though it is apparently no different to any other directory. Can > anyone enlighten me about this? Yes, that's true. The first time a directory is hard linked, both directories become hard links. Once something is hard linked, there is no concept of the "original" directory, just 1 or more hard links. Not sure why the finders failing- I'd have to give it a try and look into it further. At the very least, you should probably file a bug. -Kevin Elliott kelliott(a)mac.com http://web.mac.com/kelliott/ _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/tegtmeye%40eecis.udel.… _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… I'm not sure they are doing what you are accusing them of. Every flavor of *nix that supports it has some nonportable nuance. Hard linking to directories is implementation defined behavior-end of story. See http://www.opengroup.org/onlinepubs/009695399/functions/link.html In most circles, this means that the implementors can do whatever stable or unstable thing pleases them, especially since it really isn't documented. This could very well be a .01 release that only works in the specific case of how time machine is using it. In short, it is hard to get mad at flakey behavior when your playing around with the bleeding edge. Remember when Microsoft was busted using secret APIs to make their in-house apps better than anyone else's apps, and everyone though that stunk and was anti-competitive? I don't see why this sort of stuff should be considered some kind of private detail of Time Machine. Especially since it is in the kernel, and the API is a public one. The behavior of the API is undocumented, but it shouldn't be. The behavior of all public APIs should be fully documented and available to all. BTW, I do realise that linking directories is pretty dangerous, but that's in large part because none of the utilities or libraries take the possibility into account. This is part of the reason I'm interested in how it behaves. This email sent to tegtmeye(a)eecis.udel.edu This email sent to site_archiver(a)lists.apple.com

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Re: Hard links to directories
by Chris Idou 03 Oct '08

03 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Mailer:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type:Message-ID; b=pKHWYAAtlMM/bb8Bcn4uU6dVEShu4TPEcgCx78Y0wFbb31dtPuhDnxfIVStsGji+jnDSaIxmiuj//Lz8qxYJ2FeDdkisHNMa3EziCc4D3x9O5pOPL+Z4Jiw/F/nWxuoUsK5RPvsKFC6ksQvCJYwbSmLc4+m5GPtRWf4e4/KDZrc=; On Oct 1, 2008, at 8:00 PM, Chris Idou wrote: > > A couple more questions: > > 1) How do permissions work? I notice that the system seems to stop > you doing dangerous things like hardlinking /System to somewhere, > even as root, but its not clear why this case is different. Can't shed any light on that. As someone else has mentioned, directory hard links should effectively be considered SPI. If you want help understanding them so you can work better with TimeMachine, that's great. If you think you can use them to solve some other unrelated problem, then your making a mistake and should reconsider what your trying to do. > 2) I notice that once a directory has been hardlinked, it is forever > tainted in some fashion. If I hardlink a directory somewhere, then > unlink the 2nd link, then the original directory can never be > trashed in the Finder for example. Such an attempt will fail, even > though it is apparently no different to any other directory. Can > anyone enlighten me about this? Yes, that's true. The first time a directory is hard linked, both directories become hard links. Once something is hard linked, there is no concept of the "original" directory, just 1 or more hard links. Not sure why the finders failing- I'd have to give it a try and look into it further. At the very least, you should probably file a bug. -Kevin Elliott kelliott(a)mac.com http://web.mac.com/kelliott/ _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… This email sent to site_archiver(a)lists.apple.com

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File/Folder copying under 10.5
by Al Ciplickas 03 Oct '08

03 Oct '08

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Re: CCacheServer context and unknown error code 19777
by Jacques Vidrine 02 Oct '08

02 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Hi again! On Oct 1, 2008, at 10:56 AM, Mike Tegtmeyer wrote: The kernel doesn’t know about the bootstrap namespace. Cheers, -- Jacques _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… I'm afraid this is off-topic for Darwin kernel. I'm not sure I'm convinced it is completely not. Poking around from the outside, I'm suspicious that this might be a bootstrap namespace problem. [snip] This sounds like a bug to me, although it could also be a misconfiguration. Please write up a bug report at bugreport.apple.com. This is a stock setup so I'd be curious how to troubleshoot this further and what the resolution was from the Feb thread. You could ask the thread participants, but the gssd 19777 issue may or may not be directly related to your sshd issue. The likely result of filing a bug is that engineering would work with you to troubleshoot, particularly if this happens in a stock configuration. This email sent to site_archiver(a)lists.apple.com

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Re: which processor is a thread executing on?
by Ben Gertzfield 02 Oct '08

02 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:sender :to:subject:cc:in-reply-to:mime-version:content-type :content-transfer-encoding:content-disposition:references :x-google-sender-auth; bh=XDmKRo+ZvSb5Vd8Coq6BEKK0lo6Z9rdGdWLVJ/XW6KA=; b=YELU5SOztQuimqlUbxG19s3mzmYAMZpZ2a8fZ6j6Px5TQjA/k+dC/+gGfDq4SlROQF zC/S4U47vWzxafM/Ithu1wV/BzMiWw8bg50eTGCRKiYwu1GtAg5CT/iHSRSlZLrFNwju 1Yt8BM3xSPdLaNSZtyzapq2KhJgDCJuPj43ng= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references:x-google-sender-auth; b=t3H2wuDOlD4N0D9ajrn0jTHRzSJJNXHM9HStp0Fi5Jzj6SNqgX9PjvHsHweL+ZU2qE jpglD5syN0F2vnIKPke9Tak8Ivu7iFznzHbez1PRaXlRWfWnZDLphda8R/cG6Cvht+hW AAXpFm4MdKV9lmTweyFd5gdDmmEjexIxlqNrk= On Thu, Oct 2, 2008 at 10:45 AM, Terry Lambert <tlambert(a)apple.com> wrote: > There are so many good technical reasons as to why it would be a BAD design > choice, it's hard to know where to start, so I won't. One place that per-thread CPU pinning (or thread group scheduling) really is necessary is for scheduling of a multiprocessor virtual machine. In this case, if I have N threads (each of which is a virtual CPU of a virtual machine) I want to make sure they're either all scheduled concurrently on separate physical CPUs, or that none are scheduled. If only one of my N threads is scheduled when the virtual machine is busy, it's quite likely that one of the other (N - 1) virtual CPUs holds a resource or lock that the currently-scheduled thread needs. That means the currently-scheduled thread will spend a majority of its time looping in a spinlock, waiting for the one of the other threads to be scheduled. That just chews up CPU, when I'd rather give that CPU time to other processes' threads, until all of my virtual CPU threads can be concurrently scheduled. I can't currently do this with Mac OS X's scheduler, as far as I know. I just have to hope that all my virtual CPU threads happen to be scheduled concurrently. Ben _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… This email sent to site_archiver(a)lists.apple.com

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Re: Hard links to directories
by Kevin Elliott 02 Oct '08

02 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com On Oct 1, 2008, at 8:00 PM, Chris Idou wrote: A couple more questions: -Kevin Elliott kelliott(a)mac.com http://web.mac.com/kelliott/ _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… 1) How do permissions work? I notice that the system seems to stop you doing dangerous things like hardlinking /System to somewhere, even as root, but its not clear why this case is different. Can't shed any light on that. As someone else has mentioned, directory hard links should effectively be considered SPI. If you want help understanding them so you can work better with TimeMachine, that's great. If you think you can use them to solve some other unrelated problem, then your making a mistake and should reconsider what your trying to do. 2) I notice that once a directory has been hardlinked, it is forever tainted in some fashion. If I hardlink a directory somewhere, then unlink the 2nd link, then the original directory can never be trashed in the Finder for example. Such an attempt will fail, even though it is apparently no different to any other directory. Can anyone enlighten me about this? Yes, that's true. The first time a directory is hard linked, both directories become hard links. Once something is hard linked, there is no concept of the "original" directory, just 1 or more hard links. Not sure why the finders failing- I'd have to give it a try and look into it further. At the very least, you should probably file a bug. This email sent to site_archiver(a)lists.apple.com

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Re: which processor is a thread executing on?
by Terry Lambert 02 Oct '08

02 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com There is no such thing regarding the fb kernel for the same reasons aka terry's answer anyway it could have a guardian to handle the case of a cpu-off/bind As I said beside of any technical challenge this is a choice -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… On Oct 1, 2008, at 10:29 PM, mm w <openspecies(a)gmail.com> wrote: There are so many good technical reasons as to why it would be a BAD design choice, it's hard to know where to start, so I won't. This email sent to site_archiver(a)lists.apple.com

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Re: Hard links to directories
by Michael Smith 02 Oct '08

02 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com On Oct 1, 2008, at 7:25 PM, Chris Idou wrote: = Mike _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… OS-X 10.5 now allows you to hard link directories. "allows" is probably the wrong way to describe this. "Fails to prevent" is more correct. Don't hardlink directories. Yes, the system call succeeds. No, it doesn't work the way you think it should, and that's not considered a problem. This email sent to site_archiver(a)lists.apple.com

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Re: Hard links to directories
by mm w 02 Oct '08

02 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to :subject:cc:in-reply-to:mime-version:content-type :content-transfer-encoding:content-disposition:references; bh=LHITqDfg6TlrzxBPqf651ywKS2d7cL8x9HKFUguY7Zs=; b=wYCT/gyZIAy+ftfkMXLLf09MFGV2Z3Ur3HkOFnSEhEtCgK6tEG92wyWAfwjyzk4bKm 3Jpugzhr0a2dK14Euhcq4+SxUpmj/UGSog+13r8pHg04ybUhzjZF6xY5YOZlazzHUQOK 7P6p5DUMs4cBYV1HG5KDWYL0+ZPfWEIJ4wK68= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=LEdXXdfWR8U8V3wVxWkbnpo+QEOrbsmkKSbG4yBuigvyEGdLZ0JR7Ed5bZNyZcloGY nveLMFdvuAnnAHcIoI1NdvC2pwyMpZNe5cryImAnkOoJ0lOKVrauxJZOm47LPHIfRlqH sAlt1uSDJRfKbtQwtLOgmRHYEO/aes8nSeHIM= Hi chris yes as you noticed traditional tools are not abble to detect or handle it a hardlink anyway you should create your own tool to list the attrs there is a flag set also as you noticed there is a lock from the finder it is a good point for the health of a tm volume discouraging people to do some operations is always a good point it also why traditional tools don't handle hard links this is an old topic in the nix history there are some advantages but also a lot of problems regarding hard links On 10/1/08, Chris Idou <idou747(a)yahoo.com> wrote: > OS-X 10.5 now allows you to hard link directories. > > However the link count of the directory seems to behave in the conventional > unix way. i.e. it is the number of directories contained in that directory + > 2 for "." and "..". > > Is there a way to find out the link count for directories, or to otherwise > discover if a particular directory has hard links? > > > > > > > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) > Help/Unsubscribe/Update your Subscription: > http://lists.apple.com/mailman/options/darwin-kernel/openspecies%40gmail.com > > This email sent to openspecies(a)gmail.com > -- -mmw _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… This email sent to site_archiver(a)lists.apple.com

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Re: Hard links to directories
by Chris Idou 02 Oct '08

02 Oct '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Mailer:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type:Message-ID; b=A8aafonsd7+eiRGyzU2uh31mClycI3W7ZwHrXG5xzNLN9Xh+v3a++4fIS9Eise5PnEtzwR/QMUUxW0YAdLRKXO/fM8qIJCmATAY7fbh/YuXqV+2sHS442gpsg8zc2PB6pQr4KM03VTVEMn42VSKggZVOo8O8hTXfxmGsCcMs1Cg=; You don't have to be root. See the following article as an example of someone else who has verified this. http://www.mactech.com/articles/mactech/Vol.23/23.11/ExploringLeopardwithDT… --- On Wed, 10/1/08, Kevin Van Vechten <kvv(a)apple.com> wrote: > From: Kevin Van Vechten <kvv(a)apple.com> > Subject: Re: Hard links to directories > To: idou747(a)yahoo.com > Cc: darwin-kernel(a)lists.apple.com > Date: Wednesday, October 1, 2008, 8:12 PM > Directory hard links are really an implementation detail of > Time > Machine. It's not encouraged to create them > (they're never created on > non-Time Machine volumes), and it's not possible to > create them except > as root. > > I took a quick glance at getattrlist(2) and didn't see > this value > exported, so I'm guessing it's not (easily) > available. > > - Kevin > > On Oct 1, 2008, at 7:25 PM, Chris Idou wrote: > > > OS-X 10.5 now allows you to hard link directories. > > > > However the link count of the directory seems to > behave in the > > conventional unix way. i.e. it is the number of > directories > > contained in that directory + 2 for "." and > "..". > > > > Is there a way to find out the link count for > directories, or to > > otherwise discover if a particular directory has hard > links? _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.… This email sent to site_archiver(a)lists.apple.com

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