IRC log of #maemo for Thursday, 2014-05-08

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DocScrutinizer05~cauldron07:18
DocScrutinizer05~wiki cauldron07:18
infobotAt http://en.wikipedia.org/wiki/Cauldron (URL), Wikipedia explains: "{{Other uses}} in a traditional ""bogrács"" (cauldron)]] A 'cauldron' (or 'caldron') is a large metal pot (kettle) for cooking and/or boiling over an open fire, with a large mouth and frequently with an arc-shaped hanger. The word cauldron is first recorded in Middle English as "caudroun" (13th century). It was borrowed from Old Northern French or Anglo-Norman "caudron" T. F. Hoad, ...07:18
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Maxdamantusadd thereto a tiger's chaudron for the ingredients of our cauldron.09:37
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DocScrutinizer05~dict chaudron09:50
infobotDictionary 'chaudron' (2): \Chau"dron\, n. See {Chawdron}. [Obs.] [1913 Webster] ;; kaldaunen guts, bowels, LL. calduna intestine, W. coluddyn gut, dim. of coludd bowels.] Entrails. [Obs.] [Written also {chaudron}, {chauldron}.] --Shak. [1913 Webster].09:51
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DocScrutinizer05the heck, wikipedia doesn't even know the words used to explain what's chaudron09:58
DocScrutinizer05well, I know guts and intestine09:59
DocScrutinizer05but wtf is kaldaunen, calduna, coluddyn, coludd ?10:00
MaxdamantusThey're not words in common use.10:00
DocScrutinizer05ooh, Kutteln10:02
DocScrutinizer05seems a tiger doesn't have any those10:03
DocScrutinizer05ruminant has rumen10:04
MaxdamantusApparently that means tripe, which is basically intestines as a dish.10:06
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Maxdamantususually lamb/mutton afaik10:07
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DocScrutinizer05http://en.wikipedia.org/wiki/Tripes yep10:09
DocScrutinizer05http://en.wikipedia.org/wiki/Saure_Kutteln10:09
MaxdamantusOh, no, it's the stomach, not intestines.10:09
MaxdamantusMaybe haggis is the intestines.10:09
* Maxdamantus hasn't eaten either.10:10
DocScrutinizer05well, stomach is intestines as well in my book10:10
Maxdamantusintestines are below the stomach.10:10
DocScrutinizer05me neither °°*°D-:10:10
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DocScrutinizer05ooh, you're right. My idea of what are intestines been flawed10:12
DocScrutinizer05seems Miriam Webster is also kinda mistaken on Kaldaunen then10:13
Guest98402I'm having trouble mounting my n900 HDD on my GNU/Linux desktop. When I connect it and select mass storage mode, I get a /dev/sdb, but no /dev/sdb1 or 2 or something. There's nothing to actually mount.10:14
DocScrutinizer05http://de.wikipedia.org/wiki/Kutteln10:14
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DocScrutinizer05Guest98402: HDD?10:14
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MaxdamantusGuest98402: mount that.10:15
keriomass storage mode doesn't export a whole device10:15
keriojust a partition10:15
MaxdamantusGuest98402: it normally provides the single partition.10:15
DocScrutinizer05when your uSD has no partitions then it will show as /dev/sdb and be so called superfloppy format10:16
MaxdamantusGuest98402: the whole device would include swap and /home, which is in use by Maemo, so you don't want to mount that.10:16
DocScrutinizer05also what kerio said10:16
kerioi wonder if the exported swap partition is actually writeable10:16
kerioi never tried10:16
keriofor obvious reasons10:16
Maxdamantusit doesn't export it.10:18
keriomy swap partition is on the uSD10:18
kerioit's exported10:18
MaxdamantusAh.10:18
DocScrutinizer05hah!10:18
MaxdamantusThen sure, it would be.10:18
kerioisn't it locked or something like that?10:18
kerioi would expect the kernel to be quite strict with stuff like that10:19
DocScrutinizer05I'd think it's hard to get exported and same time used by system10:19
keriowhy's that?10:19
keriothe swap partition is a readable device file10:19
kerioi was wondering if it's writeable10:19
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MaxdamantusHm. Linux (maybe POSIX, can't remember) has a mechanism to lock parts of files.10:19
DocScrutinizer05and you had to think what for you want to mount it anyway10:19
Maxdamantusdunno if it works on devices.10:19
DocScrutinizer05unless you wanna write to raw device10:20
Maxdamantusit shouldn't be hard to export it.10:20
MaxdamantusI'd be surprised if the OS refused to export the SD device while part is used as swap.10:21
DocScrutinizer05I'd rather worry if system still can write to swap when it got exported10:21
Maxdamantusprobably just unmounts /media/mmc*10:21
DocScrutinizer05:nod:10:22
MaxdamantusIt can.10:22
Maxdamantusneither using swap nor exporting with g_file_storage locks anything.10:22
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DocScrutinizer05right10:23
DocScrutinizer05kerio: so go ahead write some mp3 or wav data to swap, watch your N900 starting to sing and dance! ;-P10:23
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Maxdamantusphones as mass storage devices is silly anyway.10:24
DocScrutinizer05I'd honestly blacklist any swap partition from export10:24
DocScrutinizer05I mean there's a reason why I pushed that blacklist into CSSU ;)10:24
MaxdamantusIt's already powerful enough to run a filesystem server.10:24
* Maxdamantus just loads g_ether on boot.10:25
DocScrutinizer05hey!10:25
DocScrutinizer05H-E-N?10:25
MaxdamantusNo.10:25
Maxdamantusit's the Linux kernel module that acts as an ethernet device.10:26
DocScrutinizer05ooh, so the device pretends to be a NIC10:26
MaxdamantusYes.10:26
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keriophones as network cards is silly anyway.10:27
MaxdamantusYes, but it's better than as block devices.10:27
keriowhy isn't g_null the default behaviour anyway?10:27
DocScrutinizer05well, unless you use the modem10:27
DocScrutinizer05to actually access "the internet"10:27
DocScrutinizer05which is best served via ethernet10:28
DocScrutinizer05err network10:28
Maxdamantuswire10:28
DocScrutinizer05yeah10:29
DocScrutinizer05TCP/IP10:29
* Maxdamantus uses it for rsync and for Bluetooth.10:29
DocScrutinizer05rsync? that's running via cronjob and WLAN here10:30
Maxdamantusrsync over ssh.10:30
DocScrutinizer05real joy to read the cronjob's mails to root10:30
Maxdamantusjust for one-off things, not periodic syncs/backups.10:30
DocScrutinizer05~jrtools10:31
infobotsomebody said jrtools was http://wiki.maemo.org/User:Joerg_rw/tools10:31
DocScrutinizer05actually http://wiki.maemo.org/User:Joerg_rw/tools#backup10:31
DocScrutinizer05extremely convenient10:31
keriooffline backups are the one true way10:33
DocScrutinizer05offline?10:33
* DocScrutinizer05 idly wonders if somebody already pondered to create a striped raid from eMMC and uSD10:34
Guest98402Maxdamantus: DocScrutinizer05 yeah, I mean the regular 28GB partition10:35
kerioDocScrutinizer05: after a successful halt10:35
DocScrutinizer05Guest98402: mount /dev/sdb /media -t vfat10:36
MaxdamantusI'm going to eventually run btrfs across the eMMC and SD.10:36
DocScrutinizer05:-D10:36
* Maxdamantus should get around to writing that alternative phone thing so he can stop using Maemo and use a newer kernel.10:37
Guest98402Thanks DocScrutinizer05 that worked10:37
DocScrutinizer05yw :)10:37
Guest98402I just wonder why pcmanfm and other file managers can't mount it themselves anymore, though10:37
* Maxdamantus wrote most of a 9p implementation in Go with a better interface than the other 9p implementations.10:37
Guest98402That used to work without problems10:38
DocScrutinizer05don't forget to sync and umount before you unplug!10:38
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Guest98402Is sync still necessary if you umount?10:38
MaxdamantusNo.10:38
DocScrutinizer05good question10:38
DocScrutinizer05prolly not10:38
Maxdamantusassuming it is fully unmounted.10:39
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MaxdamantusYou can mount the same filesystem in different places.10:39
Maxdamantusso if you "unmount" one, it's not actually unmounted.10:39
antithesis_Yeah, well, I won't do that10:39
antithesis_What about the other way around? Can you sync, then unplug without umounting?10:39
MaxdamantusDepends on the filesystem.10:40
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antithesis_FAT filesystems10:40
MaxdamantusShould be fine.10:40
Maxdamantusas long as you don't write anything after the sync.10:41
DocScrutinizer05dd if=image.bin of=/dev/sdc to flash a complete image to a uSD took >60s for sync.10:41
kerioanswer = NO10:41
DocScrutinizer05after dd finished10:41
keriothere's so much shit going on in a modern linux system10:41
kerioyou can't be sure10:41
DocScrutinizer05mount -o remount,ro /media10:42
kerioDocScrutinizer05: i would expect that to not necessarily sync10:42
MaxdamantusYes, you can do that.10:42
DocScrutinizer05sure it doesn't sync, but after sync you can be sure10:43
MaxdamantusIt does necessarily sync.10:43
DocScrutinizer05the device can't go r/o before all buffers got flushed10:43
keriothe mounted partition is going r/o10:44
MaxdamantusSo the mount call hangs until that happens.10:44
DocScrutinizer05dunno if it forces sync, or just idles and waits10:44
DocScrutinizer05prolly should force10:45
MaxdamantusIt wouldn't just idle and wait.10:45
Maxdamantusbut imo, that's what sync should do.10:45
MaxdamantusIt's not usually :(10:45
DocScrutinizer05no, sync actively flushes the buffers10:46
zGrrmoin :)10:46
DocScrutinizer05moinmoin10:46
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MaxdamantusNot really.10:47
DocScrutinizer05sync takes no parameters afaik, and that sucks10:47
MaxdamantusThe system will continuously be writing dirty stuff as long as there's stuff to write.10:47
Maxdamantusso sync/fsync means "wait until the writeback cache has passed the current moment in time"10:48
Maxdamantusbut they usually additionally send some sort of commit to the filesystem.10:48
DocScrutinizer05wut? there's a dirty-flush-timeout that's up to 1 minute on laptops etc10:49
Maxdamantusand fsync might actually prioritise things.10:49
DocScrutinizer05I'd expect sync to "increase the pressure"10:49
DocScrutinizer05sync(1) that is10:50
MaxdamantusAh yeah, when the writeback cache isn't stressed.10:50
antithesis_oshit what did I ignite10:50
antithesis_still about sync10:50
DocScrutinizer05echo 500 > /proc/sys/vm/dirty_expire_centisecs10:51
DocScrutinizer05rcS10:52
MaxdamantusI think it should only be up to the computer operator to "increase the pressure".10:52
Maxdamantusso calls like fsync should be there for processes to know when the stuff they wrote has been written.10:53
DocScrutinizer05which he did, by issueing a sync command10:53
DocScrutinizer05I'm not talking about fsync(2)10:54
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DocScrutinizer05anyway all info about sync, fsync and fdatasync seem to suggest that those function calls are kernel and executed immediately11:02
DocScrutinizer05"the kernel flushes all buffers"11:02
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MaxdamantusWonder if Linux provides a passive version of fsync.11:06
MaxdamantusIf you only want to know when some data has been written.11:07
DocScrutinizer05doesn't seem so. But I just learned that (f)sync even is supposed to flush drive cache11:07
Maxdamantuseg, in a CoW system, you'd do that to know when a revision has been completed, so you can know that it's safe to reuse space from the revision before it.11:08
DocScrutinizer05>> This includes writing through or flushing a disk  cache if present.<<11:08
DocScrutinizer05yeah, there SHOULD be such function call11:09
MaxdamantusThat should be what fsync itself does.11:09
DocScrutinizer05no, fsync serves other purpose11:10
MaxdamantusVery little other, except in distributed systems.11:10
Maxdamantuswhere you want to tell peers that the data has been safely written, as quickly as possible.11:11
DocScrutinizer05right, fsync is a bit... nonsensical for purposes of e.g. safe shutdown etc11:11
DocScrutinizer05sync otoh11:11
DocScrutinizer05generally speaking fsync makes sure your data is "safe"11:12
MaxdamantusI'd say generally speaking it doesn't.11:13
MaxdamantusIt provides a way for you to make sure your data is safe.11:14
DocScrutinizer05I guess there might be a option bit in write() to say "no buffering", then you do blocking write() and here you are11:14
Maxdamantusby letting programs know when a future revision of something has been completely written.11:14
DocScrutinizer05?11:15
Maxdamantusfsync doesn't actually provide a way to know that your data is safe.11:16
Maxdamantusa milisecond after fsync calls, someone else might've overwritten it.11:16
DocScrutinizer05fsync (and fdatasync) says "write this now, I don't want to risk it getting lost on unadvertised brownout"11:16
DocScrutinizer05and with your overwritten data you're really going weird now11:17
MaxdamantusSo what do you do after the fsync?11:17
DocScrutinizer05when somebody overwrites my file, well then my system is a pile of bullshot coded by monkeys11:18
MaxdamantusYou shouldn't just fsync for the hell of it.11:18
DocScrutinizer05let's see... what does mySQL do after fsync11:18
MaxdamantusIt's going to be written eventually11:18
DocScrutinizer05close the transaction maybe?11:18
MaxdamantusNon-distributed databases have a reason to do what I said fsync should do.11:19
MaxdamantusIf they want to be able to guarantee database consistency, they need something like fsync.11:19
DocScrutinizer05aha. and what is a commit in your book then?11:19
Maxdamantusbut they don't need the "force it to write now" bit.11:19
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DocScrutinizer05oh, they don't?11:20
MaxdamantusNo. The "force it to write now" doesn't help in ensuring consistency.11:20
DocScrutinizer05aha11:20
MaxdamantusThe system could lose power during the fsync or before it.11:20
DocScrutinizer05great11:20
DocScrutinizer05so what?11:20
DocScrutinizer05AFTER the fsync anyway I KNOW my data is on magenitzed bits on a disk11:21
DocScrutinizer05so I return from commit()11:21
MaxdamantusYes. That's what fsync should ensure.11:21
MaxdamantusIt shouldn't try to force anything.11:22
DocScrutinizer05aha11:22
Maxdamantusit should just wait until the data written beforehand is on the disk.11:22
DocScrutinizer05tzz11:22
DocScrutinizer05which may never happen11:22
MaxdamantusIt will happen eventually, unless there's a hardware failure.11:23
DocScrutinizer05no it won't11:23
DocScrutinizer05not in any warranted finite timespan11:23
MaxdamantusDo you mean indefinite?11:24
Maxdamantusor infinite?11:24
MaxdamantusIt will happen, eventually.11:24
Maxdamantusie, within a finite amount of time.11:24
DocScrutinizer05I mean  system with echo 5000000000 > /proc/sys/vm/dirty_expire_centisecs11:24
MaxdamantusThen it will have to wait a while.11:25
DocScrutinizer05I'd say THANKYOU to a db that takes 30min to return from a commit()11:25
DocScrutinizer05I suggest you write your own kernel and libs11:26
DocScrutinizer05since on unix or posix fsync won't do what you ask for11:26
MaxdamantusUnless it's part of a distributed system, the database shouldn't wait for the data to be on disk before returning.11:27
DocScrutinizer05maybe some other call does11:27
DocScrutinizer05AHA, you also need to write your own db then, see definition of "commit"11:27
Maxdamantuscommit in databases usually has to do with atomicity afaik11:28
DocScrutinizer05good luck with evaluating and certifying that critter11:28
Maxdamantusie, you have a bunch of stuff in a commit, which either happens or doesn't.11:28
freemangordon_hmm, isn't commit related to transactions, rather to io?11:28
MaxdamantusYes.11:28
Maxdamantus(afaik)11:28
DocScrutinizer05commit first and foremost has to do with rolling back atomic sequences of actions11:28
MaxdamantusYes.11:28
freemangordon_sure11:28
Maxdamantuswhich is what my use case of fsync is about.11:29
freemangordon_but shouldn't be related to io11:29
freemangordon_what db is that?11:29
MaxdamantusYou don't need to wait for a filesystem fsync to return before claiming a commit has finished though.11:29
freemangordon_exactly11:29
DocScrutinizer05depends on your level of consistency you expect from the db11:30
MaxdamantusThe point of the filesystem fsync is for there to always be a consistent (not corrupt) version of the DB accessible.11:30
DocScrutinizer05when your commit returns before data got written to disk, it ISN'T committed yet11:30
MaxdamantusSo you'll be able to roll back to some good copy after unexpected power loss.11:30
freemangordon_DocScrutinizer05: it is11:30
MaxdamantusTo do that, you need to make sure you haven't overwritten all good copies.11:31
freemangordon_as your inserts/updates are in the journal11:31
MaxdamantusSo you either need some WORM system, or something based on a passive fsync.11:31
DocScrutinizer05freemangordon_: when system goes down after commit returns but before buffers flushed, you're fsckd11:31
Maxdamantus(with the WORM system, you'd additionally need the guarantee that writes are ordered)11:31
antithesis_Okay, okay, I'll just use umount...11:32
freemangordon_sure, and I've seen that11:32
freemangordon_with oracle on solaris :)11:32
DocScrutinizer05that's why I say "depends"11:32
freemangordon_duplicated primary keys :D11:32
freemangordon_but it is not db job to care about fs11:33
freemangordon_because begin/end transaction, commit, etc is related to db, not to fs11:33
freemangordon_anyway, back to my job :)11:34
DocScrutinizer05anyway demanding a change of fsync(2) sematics so you don't need to use sth like a non-buffered blocking write() is nonsensical11:34
Maxdamantusin Linux, it's ultimately up to the filesystem implementation to provide the semantics.11:35
Maxdamantusand it seems reasonable to offer different meanings as mount options.11:36
MaxdamantusI'd like to use btrfs without a log.11:36
MaxdamantusSo if I lose power, I'll just lose up to 30s of activity.11:36
MaxdamantusI don't need to guarantee to other people that I've saved their data.11:37
DocScrutinizer05whatever you like11:37
DocScrutinizer05toldya, linux is FOSS, go and fork!11:38
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DocScrutinizer05since I don't see another way to redefine the clearly specified and fixed sematics of an existing function call when you as well could create a new function call that does what you ask for11:39
DocScrutinizer05man 2 fsync11:40
MaxdamantusMost proper uses of fsync would work with either semantics.11:41
DocScrutinizer05>>fsync()  transfers  ("flushes")  all  modified in-core data of (i.e., modified buffer cache pages for) the file referred to by the file descriptor fd to the disk device<<11:41
MaxdamantusI doubt a database is actually going to wait until the data is on disk before returning from a commit.11:41
DocScrutinizer05not "waits until that happens, eventually"11:41
MaxdamantusThat will just slow stuff down.11:41
MaxdamantusUnless you've configured the database to do it.11:41
Maxdamantuswhich might be useful in distributed systems.11:41
DocScrutinizer05exactly ;)11:42
DocScrutinizer05or in high security systems11:42
DocScrutinizer05where a commit is a commit is a commit11:42
Maxdamantusif the information is contained locally, there's usually the excuse "well, what if it crashed before the fsync? the data's lost anyway"11:42
DocScrutinizer05irrelevant, the transaction gets rolled back11:43
MaxdamantusRolled back to what?11:43
DocScrutinizer05to "money on account A"11:43
MaxdamantusHow does it know where that is?11:44
DocScrutinizer05*sigh*11:44
MaxdamantusWhat if the "money on account A" hadn't been commited to disk yet?11:44
DocScrutinizer05eh?11:44
DocScrutinizer05it *has* been, otherwise it wasn't on account A so nothing to move from A to B11:45
MaxdamantusIf you make two transactions: B → A, A → C, there are three possible places for the money to be.11:46
MaxdamantusYou have to roll back to the state you know is not corrupt.11:46
DocScrutinizer05if you make two transactions, then they are atomic each and unentangled11:46
Maxdamantusnot necessarily the one before the last.11:46
DocScrutinizer05you can't do A->C before B->A got committed11:48
MaxdamantusYou do it by keeping all states accessible, except for ones before the last one you know has been completed.11:48
MaxdamantusSo if you know the money-in-A state has been completed, you can forget about the money-in-B state.11:48
Maxdamantus(completed as in: all information about that state is on disk)11:49
DocScrutinizer05that's called "commit"11:49
MaxdamantusNo. Commit doesn't have to ensure it's on disk.11:49
DocScrutinizer05maybe in your world11:50
MaxdamantusCommit just has to ensure either none of it or all of it happens.11:50
Maxdamantusrather than half of it.11:50
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DocScrutinizer05define 'happens'11:50
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Maxdamantusis part of an accessible state.11:50
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DocScrutinizer05gibberish11:51
MaxdamantusNot gibberish.11:51
MaxdamantusThe accessible states are the one the database is currently portraying and the ones it might roll back to after power loss.11:52
DocScrutinizer05and how's that explaining what you  meant by 'happens'?11:52
MaxdamantusYou don't want an in-between state where half of the transaction has taken effect.11:52
Maxdamantuseg, in `A → C`, you don't want to accidentally roll back to a state where both A and C have the money11:53
Maxdamantusor where neither of them have the money.11:53
DocScrutinizer05yes, exactly. Like magnetic record of account A is 5 bucks lower but those 5 bucks are moving somewhere in RAM when machine gone down11:53
DocScrutinizer05instead of got written into magnetic record of B11:54
MaxdamantusWhat happens if you write that A no longer has the money, then you write that C has the money, then you fsync, but the system crashes in the middle of it?11:54
Maxdamantusso the first write has taken effect, but the second hasn't.11:54
DocScrutinizer05then the commit didn't complete11:55
MaxdamantusThere's a magnetic record of A not having the money.11:55
MaxdamantusObviously "having a magnetic record" isn't useful on its own.11:55
DocScrutinizer05meh11:55
DocScrutinizer05are we going to discuss how transactions and commits work now?11:56
MaxdamantusI'm pretty sure that's what we've been doing.11:56
Maxdamantusat least what I've been doing.11:56
Maxdamantus20:46:24 < Maxdamantus> You have to roll back to the state you know is not corrupt.11:56
Maxdamantus20:48:10 < Maxdamantus> You do it by keeping all states accessible, except for ones before the last one you know has been completed.11:56
DocScrutinizer05not on a beginner's level11:56
MaxdamantusSo you don't actually overwrite anything about A's or C's money.11:57
MaxdamantusBecause you need to make sure at least one consistent state is accessible.11:57
DocScrutinizer05FILE A: ta:345, -5bucks;   FILE B: ta:345, +5bucks;  log: ta:345 committed11:58
DocScrutinizer05rollback from right to left all you like11:58
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MaxdamantusIf you're just appending to files, you don't need anything like sync.11:59
DocScrutinizer05aha11:59
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MaxdamantusYou just need a guarantee of ordered writes.11:59
DocScrutinizer05you're aware HDD work with sectors and blocks and such shite? They even spin12:00
MaxdamantusSo when you get power back, you read the last complete line of the log file, and truncate everything after that commit on all files.12:00
MaxdamantusA journal can give you ordered writes.12:00
MaxdamantusYou only need the metadata to be ordered in this case.12:01
DocScrutinizer05and in-order write for everything will give you a db that's blatantly useless regarding performance. Possibly even runs into deadlocks12:01
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MaxdamantusWhy would you run into deadlocks?12:02
DocScrutinizer05and it doesn't matter if you fsync your data or your journal12:02
DocScrutinizer05you need to fsync *something* anyway12:03
MaxdamantusYou don't need to. You just need ordered metadata writes.12:04
Maxdamantusif you're only appending.12:04
Maxdamantusthe fsync is useful for knowing what you can overwrite.12:04
DocScrutinizer05I'm afk12:05
DocScrutinizer05this leads nowhere anyway12:05
DocScrutinizer05particularly since I'm no db developer, I just use them every now and then12:06
DocScrutinizer05e.g to move your money to and from your bank account12:07
DocScrutinizer05and i'd not be surprised if COBOL commit definition actually requires data to get written to HDD12:08
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DocScrutinizer05afk now12:09
DocScrutinizer05re your sequential writing and rolling back arbitrary amounts, so you wouldn't need a fsync: alas e.g. a ATM transaction can't get rolled back, the money got released to the customer12:19
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DocScrutinizer05so you damn sure wanna release the money same point in time you do the commit to your transaction that books -200$ to the customer's account, and you wanna be sure that's in magnetic storage, not in some buffer12:22
DocScrutinizer05you can't sit on a frankenstein-fsync and wait for buffers to eventually get flushed12:25
DocScrutinizer05in 5 minutes12:25
DocScrutinizer05for a system that has absolutely no dynamic input data to deal with, and doesn't matter when the printout with the result of all your equations and transactions falls off the printer, you may get away with your approach12:34
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MaxdamantusYes. That's an example of a distributed system.12:57
MaxdamantusYou have to tell someone else that the commit is permanent, and optimially as quickly as possible.12:57
Maxdamantus(you wouldn't want to wait a minute for the data to be flushed before responding to an ATM request)12:58
MaxdamantusWhen the ATM server dies, the customer doesn't.12:58
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DocScrutinizer05I don't know what to complain about... My GPS seems to work better than ever. After enabling Location Test indoors next to a closed window, I hardly could enable sat view fast enough to see the last 2 of 6 sats turning green. After ~10s I had a 4-sat fix19:08
DocScrutinizer05and GPS had not been used for at least 2 weeks before19:08
DocScrutinizer05AGPS, supl.google.com19:10
DocScrutinizer05SIM activated, WLAN for internet access19:11
bencohI thought supl.google didnt work anywore19:11
DocScrutinizer05O2-Germany19:11
bencohanymore*19:11
DocScrutinizer05*shrug*19:11
bencoh(my mobile operator provides me a supl anyway)19:11
DocScrutinizer05possibly it doesn't need any supl, since usually the assistance is via WWAN19:12
bencohWWAN ?19:12
DocScrutinizer052/3G19:12
DocScrutinizer05~wwan19:12
DocScrutinizer05o.O19:12
DocScrutinizer05anyway19:12
DocScrutinizer05~gsm-agps19:13
infoboti heard rrlp is the Radio Resource LCS (Location Service) Protocol as specified first in GSM TS 04.31, or http://security.osmocom.org/trac/wiki/RRLP19:13
bencohhmm, can the n900 use something else than supl for that ?19:13
DocScrutinizer05^^^19:13
DocScrutinizer05http://en.wikipedia.org/wiki/RRLP19:13
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bencohright but that doesn't give infos needed for gps stuff19:14
DocScrutinizer05prolly 3G helps a lot, via E-OTD19:14
bencoh(ephemerids and all)19:14
bencohor does it ?19:14
DocScrutinizer05rrlp does19:14
DocScrutinizer05it's basically supl via wwan19:15
DocScrutinizer05well, part of it is19:15
bencohoh, okay19:15
bencohinteresting19:15
DocScrutinizer05there's a system and a user layer iirc19:15
DocScrutinizer05and on 3G there's E-OTD19:15
DocScrutinizer05which isn't specified as giving feedback to MS19:16
bencohthe MS-assisted GPS part I guess ?19:16
DocScrutinizer05but also nobody says it mustn't19:16
DocScrutinizer05aiui E-OTD has no MS-based mode19:17
DocScrutinizer05the enodeb doesn't share sufficient info to MS to do that on-board19:18
DocScrutinizer05but enodeb could return the result of E-OTD to MS19:18
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DocScrutinizer05NB that for GSM/2G there's no such thing like E-OTD19:20
bencohno E-OTD for me then :)19:21
DocScrutinizer05at least not in specs. Carriers could do passive (from MS POV) OTD triangulation, when they add special equipment to BTS19:21
DocScrutinizer05passive OTD would mean: make MS send any arbitrary thing, check timing difference as seen by receivers of at least 3 BTS19:22
DocScrutinizer05for that the BTS need special equipment to precisely sync to each other and also precisely measure time of arrival of signal from MS19:23
bencohhmm19:24
DocScrutinizer05it's unclear which providers equipped how many of their BTS with such additional gear19:24
DocScrutinizer05anyway GPS based RRLP is defined also for 2G19:27
DocScrutinizer05afaik19:27
DocScrutinizer05yep, wiki clearly states it19:27
DocScrutinizer05>>Radio resource location services (LCS) protocol (RRLP) applies to GSM and UMTS Cellular Networks<<19:28
bencohgood to know19:29
bencohdoesn't that mean  supl should be useless then ?19:30
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DocScrutinizer05well, as long as your carrier provides it via RRLP it actually might be useless19:38
DocScrutinizer05NB the N900 GPS is controlled by modem, not by main CPU19:39
bencohI should test it some time19:39
bencohyeah I know19:39
DocScrutinizer05RRLP is the reason for that19:39
bencohbtw how does main cpu feeds the gps with supl results ?19:40
DocScrutinizer05a god question19:40
DocScrutinizer05good19:40
bencohthat goes with all the gps-related secrets ?19:41
DocScrutinizer05there are some (usually proprietary) AT commands (or in case of BB5 modem: ISI messages) to send supl data to modem and from there to GPS system19:41
DocScrutinizer05see the *closed-blob* mini tool Nokia provided for clearing position cache19:42
bencohyou mean ssi-encapsulated AT commands ?19:42
bencoh(ssi/hsi)19:43
DocScrutinizer05for debugging purposes when we had that GPS-doesn't-get-fix issue19:43
DocScrutinizer05I don't think ISI protocol is anything like "AT encapsulated into whatever"19:43
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DocScrutinizer05it's more like tcp/ip19:44
DocScrutinizer05with slots/ports for certain services19:44
bencohyeah I got confused, misread "there are some (usually proprietary) AT commands (or in case of BB5 modem: ISI messages)19:44
DocScrutinizer05we got pnatd to convert AT to ISI19:45
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DocScrutinizer05though that critter is so small and so little result from string(1) it, I could even figure they transport the raw ascii to BB5 via ISI, so actually some form of AT-over-HSI19:46
DocScrutinizer05prolly BB5 runs an AT-interpreter service of some sorts, on some slot/port19:47
DocScrutinizer05but that's not the recommended and usual way to communicate with ISI modem19:47
DocScrutinizer05disclaimer: all AIUI/AFAIK19:48
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DocScrutinizer05anyway I'm pretty convinced that BB5 does E-OTD on 3G19:49
DocScrutinizer05I could't think of any other explanation for a stable fix after <5s19:49
DocScrutinizer05*indoors* even19:49
DocScrutinizer05oooh, and O2 prolly still runs their "homezone" tariff, which is supposed to knpow about MS position within a circle of iirc 500m around your home19:51
DocScrutinizer05so odds are O2 has a vital interest in running RRLP/E-OTD19:52
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DocScrutinizer05I could even figure they do a E-OTD by default, each time a communication with MS happens19:53
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DocScrutinizer05hmm, according to http://www.teltarif.de/festnetz-nummer-handy-homezone-funktioniert-technik/news/53020.html?page=2 O2 does NOT use RRLP to define homezone20:38
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bencohI suspect sfr (france) doesn't either but I'm not sure about it20:40
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DocScrutinizer05wow, seems that's a nice new virtual provider: https://www.simquadrat.de/produkte/roaming20:51
DocScrutinizer05and they leaked a interesting info there: they call theri own network "sipgate netz" ;-)20:52
DocScrutinizer05sipgate is a great SIP-VoIP provider I'm using since err 14 years?20:53
DocScrutinizer05seems now they go GSM/UMTS20:53
DocScrutinizer05ok, 9 years, not 1420:55
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DocScrutinizer05anyway EU-wide free voice roaming, and data roaming that's not take an arm and a leg from you, like other tariffs/providers do21:04
DocScrutinizer05and Germany-wide geo-number/landline-number21:04
DocScrutinizer05that's awesome and pretty much in line with what Sipgate offers for VoIP21:05
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DocScrutinizer05bencoh: no RRLP for homezone doesn't mean the carrier doesn't run any RRLP service. Particularly in France I'd bet on it being mandatory for all carriers, to allow for proper law enforcement agencies' target tracking21:08
DocScrutinizer05as well as in GB21:09
DocScrutinizer05dunno about norway - either they hate it or they *want* it21:09
DocScrutinizer05in Germany afaik government can't enforce it21:10
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DocScrutinizer05so if O2 or other carriers do RRLP here, I'd guess they do it for location awareness of their customers' iPhone apps21:11
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DocScrutinizer05and obviously it works like a charm - I mean 5s TTFF, really?21:11
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bencohDocScrutinizer05: true21:12
* DocScrutinizer05 switches to 2G ...21:13
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DocScrutinizer05AHA! 50s till first feeble 3sat fix21:16
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DocScrutinizer05yep, reproducable. though stopping Location Test acquisition and switching to 3G, then resuming LT does _not_ result in fast TTFF. You need to quit LT and restart it, don't ask me why21:19
DocScrutinizer05absolutely obviously only 3G O2 provides data for MS-based GPS assistance21:21
DocScrutinizer05oooh, I just found the term used for what I described as "passive E-OTD alike triangualtion" above: http://en.wikipedia.org/wiki/U-TDOA21:23
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DocScrutinizer05>>Today, in the United States, Sprint and Verizon use a form of GPS known as Assisted GPS, and AT&T Mobility and T-Mobile use U-TDOA for their E9-1-1 solutions.<<21:26
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bencohhmm21:26
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kerio8 seconds for me :c21:30
DocScrutinizer058s still is great, no?21:33
kerioyeah yeah21:33
DocScrutinizer05I think the theoretical minimum on GPS are 14s21:33
DocScrutinizer05honestly GPS kinda starts becoming a niche technology and obsolete for everyday usage21:35
keriowait what21:35
kerioyou mean "pure" gps, right21:35
DocScrutinizer05yeah, obviously21:36
DocScrutinizer05since A-GPS with rich detailled assistance via RRLP is ibviously better. I mean, Location Test shows me 6 SATs with proper good S/N figures it's using after 5s21:37
kerioagps is great if you have it21:38
DocScrutinizer05while it's augmented and assisted by RRLP, it's still GPS21:38
DocScrutinizer05note that RRLP aiui also sends an ultra-exact timing reference, by telling the MS GPS about phase skew between GSM signal and the SAT signal, so the receiver doesn't need to check correlations for a window of 100ms but maybe only 5ms or less21:40
DocScrutinizer05SUPL never could do this21:40
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keriowhy is there even a skew?21:41
DocScrutinizer05huh?21:41
DocScrutinizer05why are two unrelated signals not in sync everywhere on this globe?21:41
kerioyes!21:41
kerio(i see)21:41
kerio(stupid relativity)21:41
DocScrutinizer05rather unrelativity21:42
DocScrutinizer05;-P21:42
DocScrutinizer05the WWAN signal is not necessarily in sync with GPS signals, and for sure there's a skew caused by realtive distance of MS to both the base station and the satellite21:43
bencohwell, didnt get a fix in a minute from the window (2G/operator supl)21:43
bencohweather might not help though21:44
kerioraw gps is still useful if you're somewhere with no internets and no clock21:44
DocScrutinizer05yes, sure21:44
bencohyup, getting a position in 12mn is better than nothing21:44
kerioit's also useful if you never lose the fix21:44
kerio:D21:44
DocScrutinizer05alm and eph stay valid for quize a few hours. So it's sufficient to enable GPS every 20min and you always should get an acceptable TTFF. Not <10s but for sure no 12min21:46
kerioevery 20 minutes is 20 minutes too often21:46
bencohyup21:46
bencohand yup :)21:46
DocScrutinizer05well, either you need GPS or you don't ;-)21:46
kerioisn't there a way to get an offline supl?21:46
kerioassuming a good clock21:47
DocScrutinizer05how's that supposed to work?21:47
bencohyou mean, computing eph ?21:47
kerioread clock, do calculations to figure out which satellites should be visible21:47
DocScrutinizer05eph is hard to compute, or pretty poor accuracy21:47
DocScrutinizer05that's alm21:47
keriowhat's eph?21:48
DocScrutinizer05eph takes into account the local errors in what you would expect according to alm21:48
kerio"local"?21:48
bencohephemeris21:48
bencohand almanacs should stay valid for a day anyway21:49
DocScrutinizer05weeks21:49
bencohhmm is it all transmitted ?21:50
DocScrutinizer05http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html21:51
DocScrutinizer05http://www.colorado.edu/geography/gcraft/notes/gps/gps.html#SVData21:53
DocScrutinizer05bencoh: so yes, all is transmitted in 12.5min21:56
DocScrutinizer05and then stored to N900's data cache21:57
DocScrutinizer05so one uninterrupted 13min GPS session per week should suffice21:58
DocScrutinizer05even when you don't have any SUPL or whatever21:58
keriowhat about devices that don't have enough space?21:58
DocScrutinizer05those devices don't exist, kerio21:58
keriohow much data is that?21:58
DocScrutinizer05calculate it! the data is there on http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html21:59
kerio:c21:59
DocScrutinizer05Data frames (1500 bits) are sent every thirty seconds21:59
kerio30000 bits!22:00
kerioit's 3.66KB22:00
DocScrutinizer05An entire set of twenty-five frames (125 subframes) makes up the complete Navigation Message that is sent over a 12.5 minute period.22:00
kerioanyway, make that 25 minutes22:01
kerioto get the data at least twice22:01
DocScrutinizer05only when you use a particularly stupid algo22:01
kerioi doubt that there's strong error correction22:01
DocScrutinizer05or have dropouts22:01
DocScrutinizer05there are parity bits, a few of them22:02
DocScrutinizer05but yeah, you shouldn't have any significant dropouts22:02
DocScrutinizer05I guess >1s is a sure killer22:03
DocScrutinizer05>>Data bit subframes (300 bits transmitted over six seconds) contain parity bits that allow for data checking and limited error correction.<<22:04
DocScrutinizer05http://www.colorado.edu/geography/gcraft/notes/gps/gif/databits.gif22:05
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DocScrutinizer05this is a very nice anim-gif, to understand how GPS receiver determines SAT (aka C/A RNG code) and time delay: http://www.colorado.edu/geography/gcraft/notes/gps/gif/bitsanim.gif22:13
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DocScrutinizer05note that you need to use local sliding code pattern to compare, for all SAT in vicinity, and each local pattern needs to get streched according to doppler seen from SAT's velocity relative to you22:14
DocScrutinizer05assistance helps reduce number of patterns to feed to correlator to spot the SAT22:15
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DocScrutinizer05modern chips have many of those correlators22:16
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DocScrutinizer05ultra-high sensitivity receivers work by extending the time of comparing the patterns, often up to a minute or more22:19
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keriomh, so they actually take longer to get a fix?22:20
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DocScrutinizer05sure22:23
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DocScrutinizer05they still may get a fix after 1min, when other standard receivers already failed22:24
DocScrutinizer05on a good signal they are no slower than a standard chip22:24
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kerioi see22:27
DocScrutinizer05those chips probably need magnitudes more storage and possibly also more computational grunt to accomplish the task22:28
DocScrutinizer05s/storage/memory aka RAM/22:29
infobotDocScrutinizer05 meant: those chips probably need magnitudes more memory aka RAM and possibly also more computational grunt to accomplish the task22:29
DocScrutinizer05afk, cya in 2 days22:32
RiDlooks like vacations!22:34
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