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diff --git a/microkernel/mach/rpc/discussion.mdwn b/microkernel/mach/rpc/discussion.mdwn new file mode 100644 index 00000000..00e4a012 --- /dev/null +++ b/microkernel/mach/rpc/discussion.mdwn @@ -0,0 +1,117 @@ +[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_documentation]] + + +# IRC, freenode, #hurd, 2011-06-11 + + <antrik> I don't think we have a precendence case of Mach initiating RPCs + to userspace tasks + <braunr> well mach regularly sends RPCs to external pagers + <antrik> hm, right + <antrik> anyways, the ds_ in device.defs is for use *inside* Mach, not for + the userspace interface + <braunr> what makes you think so ? + <antrik> several things + <antrik> not least the fact that without zhengda's modifications, the + device handling never calls out to userspace for all I know + <braunr> hm, it does + <braunr> for async I/O + <braunr> when the kernel has finished its I/O, it calls + ds_device_read_reply/ds_device_write_reply + <antrik> I see + <antrik> I never quite understood the _reply stuff + <braunr> although i wonder how mig is supposed to forge those names + <antrik> braunr: it isn't + <antrik> braunr: there is a separate device_reply.defs + <antrik> braunr: and it sets a *userprefix* of ds_ + <antrik> rather than a serverprefix + <braunr> i saw, yes + <braunr> ah right + <antrik> so ds still refers to the in-Mach device server, not anything + userspace + <braunr> so this is where the patch is supposed to introduce the + device_intr_notify RPC + <antrik> or at least that's my understanding... + <braunr> no, it doesn't refer to in-mach servers + <braunr> it really forges the right rpcs to be called by mach + <antrik> the definition of "RPC" is rather unclear here + <braunr> why ? + <braunr> mach has its own mach_msg() call for kernel-to-user messaging + <antrik> yes, but this is used only to send the reply message for the RPC + earlier initiated by userspace AIUI + <antrik> it doesn't look like there is any special RPC for async I/O + <braunr> yes, because this is the only use case they had + <braunr> hence the name "reply" + <braunr> intr_notify isn't a reply, but it uses the same mechanism + <braunr> these are declared as simpleroutine + <antrik> sure. but the fact that it isn't a reply message, but rather + initiates a new RPC, changes things from MiG point of view I believe + <antrik> right, as there is no reply to the reply :-) + <braunr> :) + <braunr> a simpleroutine is how to turn an rpc into a simple ipc + <antrik> I know + <antrik> so in _reply, we pretend that the reply is actually a new RPC, + with server and client roles reversed, and no reply + <antrik> (this is actually rather kludgy... apparently MIG has no real + notion of async replies) + <braunr> i don't understand what you mean + <braunr> simpleroutine is the explicit solution for async replies + <braunr> as stated in + http://www.cs.cmu.edu/afs/cs/project/mach/public/doc/unpublished/mig.ps + <braunr> it's not a new rpc with roles reversed + <braunr> it's not a reply either + <antrik> it might be an explicit solution for that, but it still seems + kludgy :-) + <braunr> i don't see why :/ + <braunr> would you have expected something like an option to create both + sync and async versions ? + <antrik> because it requires an extra .defs file + <antrik> yes + <braunr> ok + <braunr> well this seems cumbersome to me :) + <braunr> i prefer the simpleroutine approach + <braunr> but i agree this seems odd since mach has a high level ipc api + <antrik> anyways, my point is that the ds_ in device_reply.defs still + refers to the Mach side of things + <braunr> npnth: which package fails to build ? + <antrik> though a userspace process that actually handles the replies in an + async fashion will of course need some kind of device server too, just + like the DDE stuff... + <antrik> though naming it ds_ is confusing IMHO, because of the name clash + with the device server in Mach + <braunr> hm again, i fail to see why + <braunr> ds_ just means device_server + <braunr> and as most things in mach, it can be in kernel or not + <braunr> i mean, this is an interface prefix, i don't refer to an actual + single instance of a "device server" out there + <antrik> oh, right... DDE implements the Mach device protocol, so it *does* + do the ds_ part... but that makes the interrupt notification stuff even + more confusing + <braunr> hm + <braunr> because it provides a ds_device_intr_notify() which will never be + used, just to completely implement the interface ? + <antrik> yeah, that's what I suspect... + <braunr> sounds likely + <antrik> the device interface actually has two parts: one for "generic" + RPCs on the master device port, and one for device-specific RPCs. DDE + implements the latter, and uses the former... + <antrik> they live in separate places though I think: the individual device + RPCs are implemented in libmachdev, while the intr_ stuff is used in + libddekit probably + <braunr> it would be hairy to build otherwise + <antrik> so we *really* need to know what component npnth gets the error + with + <antrik> braunr: nah, not really. that's why we always have a separate + prefix for the server routines in Hurd RPCs + <braunr> right, i really need to read about mig again + <antrik> it's pretty normal for a translator to both implement and use an + interface |