June 2008 - Darwin-kernel - lists.apple.com

Switching Planes
by Robert Kukuchka 24 Jun '08

24 Jun '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Thanks in advance, Rob _______________________________________________ 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.… Is there an easy way to "switch planes" for iteration within the IORegistry? Or perhaps I'm missing some fundamental concept. Essentially I've got USB devices that I'm finding through notifications. From there I want to discover information within the context of the service plane. It seems silly for me to have to start a the root of the service plane. Can IOUsbDevice act as a "via" to another plane? The specific context is I wish to discover the IOSerialBSDClients a device publishes. My thought was to get the USBDevice (such as in USBNotificationExample), then iterating the children of that device. This email sent to site_archiver(a)lists.apple.com

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Re: IORegistryExplorer
by Herb Petschauer 23 Jun '08

23 Jun '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=yfTkqojruYe8oLcXLf6ltiBjiputpAx2rcTQ010pgog=; b=WoB3q5LTBd81dp/NB5omWr8qEqdD4ox222esmbrqHfxP6Fjp/PRoqPWOEkB8LzvMKa z64X9osJ+ZUwWBxv0FdeEkYkkXZBDrBc2TI8QzNw+ZdxV5ULjigLKphbClwxLGJeXam8 ucqQ0yCVLFJoITjIdrLehvkuWdXJ+DwLFIzRU= 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=VhxPQXXEW1mjzonfYXIE5h3JNXMtP/7pWzYfOEUrCsyXG9lg5yV55/cRDqPbDV+N7U p9eX4BjSIlotqMvcDwelS96mEbJQa6xbFhyPOQmjalEtbDVYtG+64FkWsFHyi0MxGC60 YUFTISL8KHAfQLi5rxJrVw0id2CfNzmIg54tc= Hmm, yeah I've only got the 10.4.5 source on my machine at the moment so I am out of date :-) Thanks for the heads up 2008/6/23 Nik Gervae <ngervae(a)apple.com>: > Actually, IORegistryExplorer has moved to another project as of Leopard. > IOKitTools still has ioreg, which does do registry traversal. > > I've been meaning to clean up IORegistryExplorer's new home to make that > source available, but other things have been taking priority for months. > > ---- > Nik Gervae > Kext management engineer, Apple Inc. > > > > On 23 Jun, 2008, at 13:39, Robert Kukuchka wrote: > >> Brilliant. Thanks! >> ~Rob >> On 23-Jun-08, at 1:33 PM, Herb Petschauer wrote: >> >>> Check out the IOKit Tools Darwin Project for the source to >>> IORegistryExplorer >>> >>> 2008/6/23 Robert Kukuchka <rob.kukuchka(a)mac.com>: >>>> >>>> Hello, >>>> I'm working on some code that traverses the IORegistry for >>>> information about our devices. Can anyone point me to some good example >>>> code? Is there any source available for IORegistryExplorer? >>>> Cheers, >>>> Rob >>>> _______________________________________________ >>>> 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/bogvardi%40gmail.com >>>> >>>> This email sent to bogvardi(a)gmail.com >>>> >> >> _______________________________________________ >> 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/ngervae%40apple.com >> >> This email sent to ngervae(a)apple.com > > _______________________________________________ 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: IORegistryExplorer
by Nik Gervae 23 Jun '08

23 Jun '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com ---- Nik Gervae Kext management engineer, Apple Inc. On 23 Jun, 2008, at 13:39, Robert Kukuchka wrote: Brilliant. Thanks! ~Rob On 23-Jun-08, at 1:33 PM, Herb Petschauer wrote: This email sent to bogvardi(a)gmail.com _______________________________________________ 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/ngervae%40apple.com _______________________________________________ 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.… Actually, IORegistryExplorer has moved to another project as of Leopard. IOKitTools still has ioreg, which does do registry traversal. I've been meaning to clean up IORegistryExplorer's new home to make that source available, but other things have been taking priority for months. Check out the IOKit Tools Darwin Project for the source to IORegistryExplorer 2008/6/23 Robert Kukuchka <rob.kukuchka(a)mac.com>: Hello, I'm working on some code that traverses the IORegistry for information about our devices. Can anyone point me to some good example code? Is there any source available for IORegistryExplorer? Cheers, Rob _______________________________________________ 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/bogvardi%40gmail.com This email sent to ngervae(a)apple.com This email sent to site_archiver(a)lists.apple.com

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Re: IORegistryExplorer
by Robert Kukuchka 23 Jun '08

23 Jun '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Brilliant. Thanks! ~Rob On 23-Jun-08, at 1:33 PM, Herb Petschauer wrote: This email sent to bogvardi(a)gmail.com _______________________________________________ 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.… Check out the IOKit Tools Darwin Project for the source to IORegistryExplorer 2008/6/23 Robert Kukuchka <rob.kukuchka(a)mac.com>: Hello, I'm working on some code that traverses the IORegistry for information about our devices. Can anyone point me to some good example code? Is there any source available for IORegistryExplorer? Cheers, Rob _______________________________________________ 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/bogvardi%40gmail.com This email sent to site_archiver(a)lists.apple.com

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Re: IORegistryExplorer
by Herb Petschauer 23 Jun '08

23 Jun '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=qMNLyzg2jB4HqkJP9MfMEdQVO80aAYnUdiT6lTiOW8I=; b=woVuDmcUa5vThgkXKtBLYtx2Ot/hqZ3gQXLvA//1utv/IKbovS0kANV2ZgUxRPFqQI ls8hvIXmjdf9Sp55pHlaC9671aRl3myGEYzpqMOUAmv4mMtxtXHzETCHstArlivKQj/I HFABE4DceEaMcpubse81cTgabak3spVW/U61k= 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=mNIb4xVU8uW6QnGx5dQiJB4Ov58ZLfk5mCO+Q3UCqVVNpzAUQT9OfGKoKuE8N3TGOV cDdjrCO1D881OZEj24+eN7dlBQUMp3x7iuBmJZ9N9TLPcEgDRTARsMBgs2BxV2GNz+8C joy9RZk8sYJbYfTjUHqrfP/GuzES3gMBMTI4o= Check out the IOKit Tools Darwin Project for the source to IORegistryExplorer 2008/6/23 Robert Kukuchka <rob.kukuchka(a)mac.com>: > Hello, > I'm working on some code that traverses the IORegistry for > information about our devices. Can anyone point me to some good example > code? Is there any source available for IORegistryExplorer? > Cheers, > Rob > _______________________________________________ > 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/bogvardi%40gmail.com > > This email sent to bogvardi(a)gmail.com > _______________________________________________ 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: IORegistryExplorer
by Brett George 23 Jun '08

23 Jun '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com User-agent: Thunderbird 2.0.0.14 (Macintosh/20080421) There is some good information in this document: http://developer.apple.com/documentation/DeviceDrivers/Conceptual/Accessing… Brett. _______________________________________________ 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.… Robert Kukuchka wrote: Hello, I'm working on some code that traverses the IORegistry for information about our devices. Can anyone point me to some good example code? Is there any source available for IORegistryExplorer? Cheers, Rob This email sent to site_archiver(a)lists.apple.com

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IORegistryExplorer
by Robert Kukuchka 23 Jun '08

23 Jun '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Hello, I'm working on some code that traverses the IORegistry for information about our devices. Can anyone point me to some good example code? Is there any source available for IORegistryExplorer? Cheers, Rob _______________________________________________ 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: multiple threads mutex, unlocking order
by Matt Connolly 18 Jun '08

18 Jun '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=default; d=soundevolution.com.au; h=Received:Cc:Message-Id:From:To:In-Reply-To:Content-Type:Mime-Version:Subject:Date:References:X-Mailer:X-Identified-User:DomainKey-Status; b=qmE4VVedfmgNEAMy/bof1q97UWDmvaMqf1yuMtULUvaIEOV3HPzGFFSeYqvLiu3Aba/zSLYkmLGdyr6k6lmv8y8dymkfqtIQ/EGrG/XtcEix1I62dfXzQDgrck5axKH8; Domainkey-status: no signature Many thanks, Terry. K: kernel extension U: user space daemon (1) U -> K : I am here and give me work, waits repeatedly for work. (2) K -> U : Here is your work (3) U -> K : Here is your result Regards, Matt On 17/06/2008, at 10:33 PM, Terry Lambert wrote: Basically (U is your daemon): U -> K : I am here and give me work ,-> | | (A) K -> U : Here is your work | `--- (a) U -> K : Here is your result and give me more work (b) U -> K : Here is your result and I quit (B) K -> U : I have no work for you; go away With the possibility of an async: (c) U -> K : Alas, I am dead! -- Terry HTH. = 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/tlambert%40apple.com _______________________________________________ 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 My implementation is very very similar to your graph below. I've just put it all together using semaphores, and it all seems to be working quite nice. (1) U communicates with an IOUserClient sub-class in K, which configures an IODataQueue object. (2) K sends work via an IODataQueue, which wakes the daemon via a CFMachPort run loop source, this kernel thread blocks waiting for the response from U, or times out. (3) U sends the response via the IOUserClient which signals the semaphore causing K(2) to continue. My IOUserClient sub-class does a semaphore_signal_all on close, so if the driver class has any threads blocked waiting on the semaphore, they will all wake up if the daemon dies. On Jun 17, 2008, at 12:47 AM, Matt Connolly wrote: Thanks, Mike. In my application, the kernel has to initiate the messaging, since it's intercepting an event in the kernel space, but the user-space process is responsible for handling it. (to reduce code in kernel, and for higher level os interfaces). Typically this is done by having user space initiate a request for work to do. The kernel blocks the completion of that request until there is actually work to do. When there is work to do, the kernel queues it to a work to do queue, and sends a wakeup to the synchonizer on which the user space process is blocked in the kernel. The (now unblocked) user space thread dequeues the information and returns it to user space, completing the request. When the work is done, the user space process servicing the kernel's request calls back down with the answer and asks for more work (same call). This effectively inverts the normal system call order, but it's what NFS daemons historically do, and it's how the external identity resolver in Directory Services works. We haven't formalized this design pattern into an API/KPI because we in general believe it's very bad to block a kernel operation on something running in user space; you can get a deadly embrace deadlock, if the user space process triggers a message to itself (through however long a chain of services), and you can get a starvation deadlock, if the user space process does not get sufficient opportunity to run. The deadly embrace is generally avoidable only by not relying on frameworks or libraries for which you have not audited the source code for Hamiltonian cycles in the call graph. The starvation deadlock is generally avoidable only by running at very high priority. Typically, this means that you run minimal code and exempt root owned processes from triggering up to user space. This makes it ideally suited for kauth and similar mechanisms, who run as root and know that root is always authorized, and significantly less suited to all other uses (for example, a firewall that pops up an authorization dialog before permitting a network request to complete). The user-space connects via a IOUserClient sub-class. Only when this sub-class is instantiated does the driver activate. So, yes, I'm checking what to do if the user-space process crashes out -> the IOUserClient sub-class will get a clientDied message, and the rest of the driver deactivates. Semaphores seem like the go. But I read somewhere that when a semaphore is signalled, that the waiting thread will not activate immediately - I was hoping that I could get this to happen to reduce latency. Alternatively, mach messaging might be best. In both of these cases, you can do a timed wait, so if the user-space process crashes, the timeout will revert to a deactive driver state. It seems, though, that there's a lack of nice IOLock type classes for semaphores and mach messages. Or have I missed something? Cheers,Matt On Jun 16, 2008, at 8:09 AM, Matt Connolly wrote: Do the IOLock lock and unlock routines have to be called from the same thread? They should, yes. If multiple threads are waiting on the IOLock, are they executed in the order that they began waiting on the Lock? No. I'm looking for a way for a kernel task to wait for a user space process to respond to a message. This is generally a bad way to do things; you want the user process to drive the messaging, not the kernel. The underlying issue is that user processes are transient and unreliable, so you need to behave correctly in the case where the process fails to complete the work, or terminates while the work is in progress. IFF we assume that you have arranged for the user process to re- start, you need to maintain queues of work items (in progress, waiting) inside the kernel so that you can re-issue work to your user process if it checks in after crashing. (And your work items need to be devised such that they can safely be re-started). Basically, I want to serialise things, so that if there are multiple kernel threads sending to the user-space process, that they will have their information processed, and be woken from their locks in the correct order. A better model is for the work items to be queued inside the kernel, and for the user process to come along and pick up these work items as it has resources available. As for "the correct order", since kernel threads run concurrently with user threads, it is entirely your responsibility to ensure ordering. You can use a global sequence number, or sort the queue, or... there are many options depending solely on what sort of ordering you're actually talking about. This email sent to tlambert(a)apple.com smime.p7s

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Re: multiple threads mutex, unlocking order
by Terry Lambert 17 Jun '08

17 Jun '08

site_archiver(a)lists.apple.com Delivered-To: darwin-kernel(a)lists.apple.com Basically (U is your daemon): U -> K : I am here and give me work ,-> | | (A) K -> U : Here is your work | `--- (a) U -> K : Here is your result and give me more work (b) U -> K : Here is your result and I quit (B) K -> U : I have no work for you; go away With the possibility of an async: (c) U -> K : Alas, I am dead! -- Terry HTH. = 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/tlambert%40apple.com _______________________________________________ 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 Jun 17, 2008, at 12:47 AM, Matt Connolly wrote: Thanks, Mike. In my application, the kernel has to initiate the messaging, since it's intercepting an event in the kernel space, but the user-space process is responsible for handling it. (to reduce code in kernel, and for higher level os interfaces). Typically this is done by having user space initiate a request for work to do. The kernel blocks the completion of that request until there is actually work to do. When there is work to do, the kernel queues it to a work to do queue, and sends a wakeup to the synchonizer on which the user space process is blocked in the kernel. The (now unblocked) user space thread dequeues the information and returns it to user space, completing the request. When the work is done, the user space process servicing the kernel's request calls back down with the answer and asks for more work (same call). This effectively inverts the normal system call order, but it's what NFS daemons historically do, and it's how the external identity resolver in Directory Services works. We haven't formalized this design pattern into an API/KPI because we in general believe it's very bad to block a kernel operation on something running in user space; you can get a deadly embrace deadlock, if the user space process triggers a message to itself (through however long a chain of services), and you can get a starvation deadlock, if the user space process does not get sufficient opportunity to run. The deadly embrace is generally avoidable only by not relying on frameworks or libraries for which you have not audited the source code for Hamiltonian cycles in the call graph. The starvation deadlock is generally avoidable only by running at very high priority. Typically, this means that you run minimal code and exempt root owned processes from triggering up to user space. This makes it ideally suited for kauth and similar mechanisms, who run as root and know that root is always authorized, and significantly less suited to all other uses (for example, a firewall that pops up an authorization dialog before permitting a network request to complete). The user-space connects via a IOUserClient sub-class. Only when this sub-class is instantiated does the driver activate. So, yes, I'm checking what to do if the user-space process crashes out -> the IOUserClient sub-class will get a clientDied message, and the rest of the driver deactivates. Semaphores seem like the go. But I read somewhere that when a semaphore is signalled, that the waiting thread will not activate immediately - I was hoping that I could get this to happen to reduce latency. Alternatively, mach messaging might be best. In both of these cases, you can do a timed wait, so if the user-space process crashes, the timeout will revert to a deactive driver state. It seems, though, that there's a lack of nice IOLock type classes for semaphores and mach messages. Or have I missed something? Cheers,Matt On Jun 16, 2008, at 8:09 AM, Matt Connolly wrote: Do the IOLock lock and unlock routines have to be called from the same thread? They should, yes. If multiple threads are waiting on the IOLock, are they executed in the order that they began waiting on the Lock? No. I'm looking for a way for a kernel task to wait for a user space process to respond to a message. This is generally a bad way to do things; you want the user process to drive the messaging, not the kernel. The underlying issue is that user processes are transient and unreliable, so you need to behave correctly in the case where the process fails to complete the work, or terminates while the work is in progress. IFF we assume that you have arranged for the user process to re- start, you need to maintain queues of work items (in progress, waiting) inside the kernel so that you can re-issue work to your user process if it checks in after crashing. (And your work items need to be devised such that they can safely be re-started). Basically, I want to serialise things, so that if there are multiple kernel threads sending to the user-space process, that they will have their information processed, and be woken from their locks in the correct order. A better model is for the work items to be queued inside the kernel, and for the user process to come along and pick up these work items as it has resources available. As for "the correct order", since kernel threads run concurrently with user threads, it is entirely your responsibility to ensure ordering. You can use a global sequence number, or sort the queue, or... there are many options depending solely on what sort of ordering you're actually talking about. This email sent to tlambert(a)apple.com This email sent to site_archiver(a)lists.apple.com

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Re: multiple threads mutex, unlocking order
by Matt Connolly 17 Jun '08

17 Jun '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=default; d=soundevolution.com.au; h=Received:Message-Id:From:To:Content-Type:Mime-Version:Subject:Date:X-Mailer:X-Identified-User:DomainKey-Status; b=WPMuBAgpuQ3S7eEMjOfdh8y2evq0t9IhfpQj/gpi1M1BHrbkg226pj9gGb+GziPAqsZavYz+NjwwuZPx0TdXCpNfjB1/KitdJTDdQgEVdDnEF6224fNPeb2SOQfGF9bu; Domainkey-status: no signature Thanks, Mike. In my application, the kernel has to initiate the messaging, since it's intercepting an event in the kernel space, but the user-space process is responsible for handling it. (to reduce code in kernel, and for higher level os interfaces). The user-space connects via a IOUserClient sub-class. Only when this sub-class is instantiated does the driver activate. So, yes, I'm checking what to do if the user-space process crashes out -> the IOUserClient sub-class will get a clientDied message, and the rest of the driver deactivates. Semaphores seem like the go. But I read somewhere that when a semaphore is signalled, that the waiting thread will not activate immediately - I was hoping that I could get this to happen to reduce latency. Alternatively, mach messaging might be best. In both of these cases, you can do a timed wait, so if the user-space process crashes, the timeout will revert to a deactive driver state. It seems, though, that there's a lack of nice IOLock type classes for semaphores and mach messages. Or have I missed something? Cheers, Matt On Jun 16, 2008, at 8:09 AM, Matt Connolly wrote: They should, yes. No. HTH. = 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.… This email sent to site_archiver(a)lists.apple.com Do the IOLock lock and unlock routines have to be called from the same thread? If multiple threads are waiting on the IOLock, are they executed in the order that they began waiting on the Lock? I'm looking for a way for a kernel task to wait for a user space process to respond to a message. This is generally a bad way to do things; you want the user process to drive the messaging, not the kernel. The underlying issue is that user processes are transient and unreliable, so you need to behave correctly in the case where the process fails to complete the work, or terminates while the work is in progress. IFF we assume that you have arranged for the user process to re-start, you need to maintain queues of work items (in progress, waiting) inside the kernel so that you can re-issue work to your user process if it checks in after crashing. (And your work items need to be devised such that they can safely be re-started). Basically, I want to serialise things, so that if there are multiple kernel threads sending to the user-space process, that they will have their information processed, and be woken from their locks in the correct order. A better model is for the work items to be queued inside the kernel, and for the user process to come along and pick up these work items as it has resources available. As for "the correct order", since kernel threads run concurrently with user threads, it is entirely your responsibility to ensure ordering. You can use a global sequence number, or sort the queue, or... there are many options depending solely on what sort of ordering you're actually talking about. smime.p7s

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