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diff --git a/open_issues/mig_portable_rpc_declarations.mdwn b/open_issues/mig_portable_rpc_declarations.mdwn deleted file mode 100644 index f5f18880..00000000 --- a/open_issues/mig_portable_rpc_declarations.mdwn +++ /dev/null @@ -1,291 +0,0 @@ -[[!meta copyright="Copyright © 2011, 2012, 2013, 2014 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_mig]] - -[[!toc]] - - -# 32-Bit vs. 64-Bit Interfaces - -## IRC, freenode, #hurd, 2011-10-16 - - <braunr> i guess it wouldn't be too hard to have a special mach kernel for - 64 bits processors, but 32 bits userland only - <youpi> well, it means tinkering with mig - <braunr> like old sparc systems :p - <youpi> to build the 32bit interface, not the 64bit one - <braunr> ah yes - <braunr> hm - <braunr> i'm not sure - <braunr> mig would assume a 32 bits kernel, like now - <youpi> and you'll have all kinds of discrepancies in vm_size_t & such - <braunr> yes - <braunr> the 64 bits type should be completely internal - <braunr> types* - <braunr> but it would be far less work than changing all the userspace bits - for 64 bit (ofc we'll do that some day but in the meanwhile ..) - <youpi> yes - <youpi> and it'd boost userland addrespace to 4GiB - <braunr> yes - <youpi> leaving time for a 64bit userland :) - - -## IRC, freenode, #hurd, 2011-11-14 - - <braunr> also, what's the best way to deal with types such as - <braunr> type cache_info_t = struct[23] of integer_t; - <braunr> whereas cache_info_t contains longs, which are obviously not - integer-wide on 64-bits processors - <braunr> ? - <youpi> you mean, to port mach to 64bit? - <braunr> no, to make the RPC declaration portable - <braunr> just in case :) - <youpi> refine integer_t into something more precise - <youpi> such as size_t, off_t, etc. - <braunr> i can't use a single line then - <braunr> struct cache_info contains ints, vm_size_t, longs - <braunr> should i just use the maximum size it can get ? - <braunr> or declare two sizes depending on the word size ? - <youpi> well, I'd say three - <braunr> youpi: three ? - <youpi> the ints, the vm_size_ts, and the longs - <braunr> youpi: i don't get it - <braunr> youpi: how would i write it in mig language ? - <youpi> I don't know the mig language - <braunr> me neither :) - <youpi> but I'd say don't lie - <braunr> i just see struct[23] of smething - <braunr> the original zone_info struct includes both integer_t and - vm_size_t, and declares it as - <braunr> type zone_info_t = struct[9] of integer_t; - <braunr> in its mig defs file - <braunr> i don't have a good example to reuse - <youpi> which is lying - <braunr> yes - <braunr> which is why i was wondering if mach architects themselves - actually solved that problem :) - <braunr> "There is no way to specify the fields of a - <braunr> C structure to MIG. The size and type-desc are just used to - give the size of - <braunr> the structure. - <braunr> " - <braunr> well, this sucks :/ - <braunr> well, i'll do what the rest of the code seems to do, and let it - rot until a viable solution is available - <antrik> braunr: we discussed the problem of expressing structs with MIG in - the libburn thread - <antrik> (which I still need to follow up on... [sigh]) - - -## IRC, freenode, #hurd, 2012-12-12 - -In context of [[microkernel/mach/gnumach/memory_management]]. - - <tschwinge> Or with a 64-bit one? ;-P - <braunr> tschwinge: i think we all had that idea in mind :) - <pinotree> tschwinge: patches welcome :P - <youpi> tschwinge: sure, please help us settle down with the mig stuff - <youpi> what was blocking me was just deciding how to do it - <braunr> hum, what's blocking x86_64, except time to work on it ? - <youpi> deciding the mig types & such things - <youpi> i.e. the RPC ABI - <braunr> ok - <braunr> easy answer: keep it the same - <youpi> sorry, let me rephrase - <youpi> decide what ABI is supposed to be on a 64bit system, so as to know - which way to rewrite the types of the kernel MIG part to support 64/32 - conversion - <braunr> can't this be done in two steps ? - <youpi> well, it'd mean revamping the whole kernel twice - <youpi> as the types at stake are referenced in the whole RPC code - <braunr> the first step i imagine would simply imply having an x86_64 - kernel for 32-bits userspace, without any type change (unless restricting - to 32-bits when a type is automatically enlarged on 64-bits) - <youpi> it's not so simple - <youpi> the RPC code is tricky - <youpi> and there are alignments things that RPC code uses - <youpi> which become different when build with a 64bit compiler - <pinotree> there are also things like int[N] for io_stat_struct and so on - <braunr> i see - <youpi> making the code wrong for 32 - <youpi> thus having to change the types - <youpi> pinotree: yes - <pinotree> (doesn't mig support structs, or it is too clumsy to be used in - practice?) - <braunr> pinotree: what's the problem with that (i explcitely said changing - int to e.g. int32_t) - <youpi> that won't fly for some of the calls - <youpi> e.g. getting a thread state - <braunr> pinotree: no it doesn't support struct - <pinotree> braunr: that some types in struct stat are long, for instance - <braunr> pinotree: same thing with longs - <braunr> youpi: why wouldn't it ? - <youpi> that wouldn't work on a 64bit system - <youpi> so we can't make it int32_t in the interface definition - <braunr> i understand the alignment issues and that the mig code adjusts - the generated code, but not the content of what is transfered - <braunr> well of course - <braunr> i'm talking about the first step here - <braunr> which targets a 32-bits userspace only - <youpi> ok, so we agree - <youpi> the second step would have to revamp the whole RPC code again - <braunr> i imagine the first to be less costly - <braunr> well, actually no - <braunr> you're right, the mig stuff would be easy on the application side, - but more complicated on the kernel side, since it would really mean - dealing with 64-bits values there - <braunr> (unless we keep a 3/1 split instead of giving the full 4g to - applications) - -See also [[microkernel/mach/gnumach/memory_management]]. - - <youpi> (I don't see what that changes) - <braunr> if the kernel still runs with 32-bits addresses, everything it - recevies from or sends through mig can be stored with the user side - 32-bits types - <youpi> err, ok, but what's the point of the 64bit kernel then ? :) - <braunr> and it simply uses 64-bits addresses to deal with physical memory - <youpi> ok - <youpi> that could even be a 3.5/0.5 split then - <braunr> but the memory model forces us to run either at the low 2g or the - highest ones - <youpi> but linux has 3/1, so we don't need that - <braunr> otherwise we need an mcmodel=medium - <braunr> we could do with mcmodel=medium though, for a time - <braunr> hm actually no, it would require mcmodel=large - <braunr> hum, that's stupid, we can make the kernel run at -2g, and use 3g - up to the sign extension hole for the kernel map - - -## IRC, freenode, #hurd, 2013-12-03 - - <azeem> I believe the main issue is redoing the RPCs in 64bit, i.e. the - Mach/Hurd interface - <braunr> mach has always been 64-bits capable - <braunr> the problem is both mach and the hurd - <braunr> it's at the system interface (the .defs of the RPCs) - <braunr> azeem: ah, actually that's why you also say - <braunr> but i consider it to be a hurd problem - <braunr> the hurd itself is defined as being a set of interfaces and - servers implementing them, i wouldn't exclude the interfaces - <braunr> that's what* - - -# Structured Data - -## IRC, freenode, #hurd, 2013-06-25 - - <teythoon> is there a nice way to get structured data through mig that I - haven't found yet? - <teythoon> say an array of string triples - <braunr> no - <teythoon> :/ - <braunr> but you shouldn't need that - <teythoon> my use case is getting info about fs translators from init to - procfs - -[[hurd/translator/mtab]], [[hurd/translator/mtab/discussion]]. - - <teythoon> should I go for an iterator like interface instead? - <braunr> depends - <braunr> how many do you need ? - <braunr> you could go for a variable sized array too - <braunr> have a look at what already exists - <teythoon> records, maybe 10-15, depends on many fs translators are running - <braunr> a variable sized array is ok if the size isn't too big (and when i - say too big, i mean hundreds of MiB) - <braunr> an iterator is ok too if there aren't too many items - <braunr> you may want to combine both (i think that's what proc does) - <braunr> be aware that the maximum size of a message is limited to 512 MiB - <teythoon> yeah I saw the array[] of stuff stuff, but array[] of string_t - does not work, I guess b/c string_t is also an array - <teythoon> how would I send an array of variable length strings? - <braunr> i'm not sure you can - <braunr> or maybe out of line - <teythoon> somehow I expected mig to serialize arbitrary data structures, - maybe it's to old for that? - <teythoon> yeah, I read about uot of line, but that seems overkill - <braunr> it is old yes - <braunr> and not very user friendly in the end - <braunr> let me check - <teythoon> we could stuff json into mig... - <braunr> see proc_getallpids for example - <braunr> we could get rid of low level serialization altogether :p - <teythoon> hah, exactly what I was looking at - <braunr> (which is what i'll do in x15) - <braunr> type pidarray_t = array[] of pid_t; - <teythoon> but that is trivial b/c its array[] of pid_t - <braunr> and always have the server writing guide near you - <teythoon> yes - <braunr> well, make one big string and an array of lengths :p - <teythoon> thought about that and said to myself, there must be a better - way that I haven't found yet - <braunr> or one big string filled with real null-terminated c strings that - you keep parsing until you ate all input bytes - <braunr> i'm almost certain there isn't - <braunr> type string_t = c_string[1024]; /* XXX */ - <teythoon> yes - <braunr> even that isn't really variable sized - <teythoon> you think anyone would object to me putting a json encoder in - /hurd/init? it is probably better than me at serializing stuff... - <braunr> try with mig anyway - <braunr> the less dependencies we have for core stuff, the simpler it is - <braunr> but i agree, mig is painful - <teythoon> would it be too hacky if I abused the argz functions? they do - exactly what I'd need - - -## IRC, freenode, #hurd, 2013-06-26 - - <teythoon> there is https://code.google.com/p/protobuf-c/ and it has a rpc - mechanism and I believe one could plug arbitrary transports easily - <braunr> please don't think about it - <braunr> we really don't want to add another layer of serialization - <braunr> it's better to completely redesign mach ipc anyway - <braunr> and there is a project for that :p - <teythoon> ive seen x15 - <teythoon> just food for thought - <braunr> i've studied google protocol buffers - <braunr> and fyi, no, it wouldn't be easy to plug arbitrary transports on - top of mach - <braunr> there is a lot of knowledge about mach ports in mig - -[[hurd/translator/mtab]], [[hurd/translator/mtab/discussion]]. - - <teythoon> but again I face the challenge of serializing a arbitrary sized - list of arbitrary sized strings - <braunr> yes - <teythoon> list of ports is easier ;) but I think its worthwile - <teythoon> so what about abusing argz* for this? you think it's too bad a - hack? - <braunr> no since it's in glibc - <teythoon> awesome :) - <braunr> but i don't remember the details well and i'm not sure the way you - use it is safe - <teythoon> yeah, I might have got the details wrong, I hadn't had the - chance to test it ;) - - <braunr> about this dynamic size problem - <braunr> a "simple" varying size array should do - <braunr> you can easily put all your strings in there - <teythoon> seperated by 0? - <braunr> yes - <teythoon> that's exactly what the argz stuff does - <braunr> you'll get the size of the array anyway, and consume it until - there is no byte left - <braunr> good - <braunr> but be careful with this too - <braunr> since translators can be run by users, they somtimes can't be - trusted - <braunr> and even a translator running as root may behave badly - <braunr> so careful with parsing - <teythoon> noted |