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-[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]]
+[[!meta copyright="Copyright © 2011, 2013 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
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<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, 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
+ <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 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
+ <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