Linux Kernel

Kernel Threads

ps ax PID TTY STAT TIME COMMAND 1 ? S 0:00 init [2] 2 ? SN 0:00 [ksoftirqd/0] 3 ? S< 0:00 [events/0] 4 ? S< 0:00 [khelper] 5 ? S< 0:00 [kblockd/0] 6 ? S 0:00 [khubd] 32 ? S 0:00 [pdflush] 33 ? S 0:00 [pdflush] 35 ? S< 0:00 [aio/0] 34 ? S 0:00 [kswapd0] 619 ? S 0:00 [kseriod] 871 ? S 0:00 [pccardd] 873 ? S 0:00 [pccardd]

Kernel Threads werden mit eckigen Klammern hervorgehoben um sie von normalen Prozessen zu unterscheiden

Kernel Prio

die priorität von prozessen wird mittels nice gesetzt [-20,19], im Linux Kernel werden Prioritäten einfacher von 0-139 dargestellt [-20,19] entspricht hierbei den prioritäten 100 - 139, der niedrigste Wert hat demnach auch die höchste Priorität

NUMA

http://lse.sourceforge.net/numa/faq/

Verteilung des Kernels im Speicher

cat /proc/iomem

Zeigt an das der Kernel erst ab dem 1. MB im Arbeitsspeicher beginnt der Code benötigt ungefähr 2.5 MB, der Datenabschnitt 0.9MB. Man sieht hier auch z.b die Adresse des BIOS ROM/RAMs, Video ROM/RAMs, usw.

Virtueller Adress Raum

Nettes Thema, wurde im Kernelbuch noch nicht beschrieben, jedoch ist dort oft davon die Rede.. Da ich's nicht verstanden hab hab ich's mir mal auf irc.oftc.net/#kernelnewbies erklären lassen :-))

02:47 <revenger1> noch wach? 02:51 <Bertl> yep yep ... 02:52 <revenger1> ich versteh absolut nicht was da noch sein sollte ausser swap und ram.. egal auch wenn das ganze virtuell ist musses doch mindestens existieren ansonsten könnte n teil von ner applikation im speicher fehlen.. 02:53 <Bertl> nein, schau ... 02:53 <Bertl> z.b. du startest java 02:53 <Bertl> java sagt dem kernel ... ich will 1GB memory (weil es dann die mm verwaltung selber macht) 02:53 <Bertl> nun wäre das kernel ja dumm, wenn es 1GB ram belegen würde ... 02:54 <Bertl> also sagt es einfach, 1GB das sind ... hmmm ..262144 pages ... 02:54 <Bertl> da nimm und werd glücklich ... 02:55 <Bertl> alle pages sind read/write protected 02:55 <revenger1> ok und wenn eine page angesprochen wird die nicht mit dem ram/swap verbunden ist wird sie angelegt? 02:55 <Bertl> d.h. wenn java nun die erste (oder welche auch immer) page anfasst 02:56 <Bertl> dann wird die entsprechend angelegt ... zuerst im ram, dann möglicherweise ausgeswappt (später) 02:56 <Bertl> dann gibts aber auch noch pages die garnicht ins swap kommen 02:56 <revenger1> ok 02:56 <Bertl> z.b. alle files die gemapped werden (seis libraries oder executables) 02:56 <revenger1> is doch so einfach :) 02:57 <Bertl> und natürlich gibts auch pages die niemals gültig werden, wie der zero page blocker oder pages die sich mit dem kernel überschneiden würden ... 02:58 <revenger1> die erklärung war eindeutig danke! 02:58 <Bertl> gern geschehen, have fun!

http://www.redhat.com/docs/manuals/enterprise/RHEL-3-Manual/admin-guide/s1-memory-virt-details.html

http://www.xml.com/ldd/chapter/book/ch13.html

PAE Physical Address Extension

(intel invention) pae makes 4 extra bits available for addressing of memory, result => 2^36 => 64GiB though still there's the limitation of 4GiB for 32 bit applications so one process _cannot_ take more than 3GiB memory on a Linux system (since the kernel takes the other GiB? for managing the process)

{ZONE DMA}? First 16MiB of memory {ZONE NORMAL}? 16MiB - 896MiB {ZONE HIGHMEM}? 896 MiB? - End

OS (Arch ia32) relation   Windows 2:2 http://tinyurl.com/4gw7q Solaris 3.75:0.25   Linux 3:1; 3.5:0.5; 4:4 (there are patches available)   FreeBSD 2:2 (also adjustable)

$ readelf --sections /usr/src/linux-2.6.9/vmlinux There are 31 section headers, starting at offset 0x31528c: Section Headers: [Nr] Name Type Addr Off Size ES Flg Lk Inf Al [ 0] NULL 00000000 000000 000000 00 0 0 0 [ 1] .text PROGBITS c0100000 001000 210c95 00 AX 0 0 16 [ 2] __ex_table PROGBITS c0310ca0 211ca0 0010a8 00 A 0 0 4 [ 3] .rodata PROGBITS c0311d60 212d60 044802 00 A 0 0 32 [ 4] .pci_fixup PROGBITS c0356564 257564 000340 00 WA 0 0 4 [ 5] __ksymtab PROGBITS c03568a4 2578a4 004828 00 A 0 0 4 [ 6] __ksymtab_gpl PROGBITS c035b0cc 25c0cc 000240 00 A 0 0 4 [ 7] __kcrctab PROGBITS c035b30c 25c30c 002414 00 A 0 0 4 [ 8] __kcrctab_gpl PROGBITS c035d720 25e720 000120 00 A 0 0 4 [ 9] __ksymtab_strings PROGBITS c035d840 25e840 009bbb 00 A 0 0 32 [10] __param PROGBITS c03673fc 2683fc 0003e8 00 A 0 0 4 [11] .data PROGBITS c0368000 269000 082478 00 WA 0 0 4096 [12] .data.page_aligne PROGBITS c03eb000 2ec000 000800 00 WA 0 0 32 [13] .data.cacheline_a PROGBITS c03eb800 2ec800 0024c0 00 WA 0 0 32 [14] .data.init_task PROGBITS c03ee000 2ef000 002000 00 WA 0 0 32 [15] .init.text PROGBITS c03f0000 2f1000 015cca 00 AX 0 0 32 [16] .init.data PROGBITS c0405ce0 306ce0 0040bc 00 WA 0 0 32 [17] .init.setup PROGBITS c0409da0 30ada0 00036c 00 WA 0 0 4 [18] .initcall.init PROGBITS c040a10c 30b10c 0001d8 00 WA 0 0 4 [19] .con_initcall.ini PROGBITS c040a2e4 30b2e4 000004 00 WA 0 0 4 [20] .security_initcal PROGBITS c040a2e8 310000 000000 00 W 0 0 1 [21] .altinstructions PROGBITS c040a2e8 30b2e8 00236f 00 A 0 0 4 [22] .altinstr_replace PROGBITS c040c657 30d657 0008e1 00 AX 0 0 1 [23] .exit.text PROGBITS c040cf40 30df40 000e60 00 AX 0 0 16 [24] .init.ramfs PROGBITS c040e000 30f000 000085 00 A 0 0 1 [25] .bss NOBITS c040f000 310000 023904 00 WA 0 0 32 [26] .comment PROGBITS 00000000 310000 005115 00 0 0 1 [27] .note.GNU-stack NOTE 00000000 315115 000000 00 X 0 0 1 [28] .shstrtab STRTAB 00000000 315115 000176 00 0 0 1 [29] .symtab SYMTAB 00000000 315764 07cb30 10 30 5da0 4 [30] .strtab STRTAB 00000000 392294 095ad2 00 0 0 1 Key to Flags: W (write), A (alloc), X (execute), M (merge), S (strings) I (info), L (link order), G (group), x (unknown) O (extra OS processing required) o (OS specific), p (processor specific)

Linux Speicherverwaltung

 * Slab(Kachel) Allocator (1994, Jeff Bonwick, sun microsystems)
 * virtueller Speicher

Beside my mind (probably had a nice evening before)

03:41 < revenger> There are screens on: 03:41 < revenger> 82922.ttyp0.revenger (Detached) 03:41 < revenger> that's not really possible with linux right? 03:41 < revenger> max pid is smallint 64767 or something like that 03:41 < revenger> or 62* ## (Added after the conversation) 65676 is it ors so don't really care about the accurat evalue since I can look it up 03:42 < revenger> just wonder about that high pidnumber on my bsd box.. never recognized that before though 03:42 < shadows> I think it's possible. 03:42 < revenger> well possible without patches? 03:42 < shadows> and smallint is like 65535. 03:42 < revenger> yes.. but 82922 03:42 < revenger> it's a pid on bsd 03:43 < shadows> yeah... I dunno. I've seen up of 70k on my linux box all the time. 03:43 < revenger> never seen that before 03:43 < revenger> even our high load webservers just have <65k pids 03:44 < revenger> just started to start over with the pids here.. 30771 and afterwards 2277.. 03:45 < shadows> I dunno. 03:45 < DrNick> /proc/sys/kernel/pid_max 03:45 -!- jayakumar2 [~jayakumar@219.95.45.130] has joined #kernelnewbies 03:45 < revenger> cat /proc/sys/kernel/pid_max 03:45 < revenger> cat: /proc/sys/kernel/pid_max: No such file or directory 03:46 -!- sindian [~sindian@va-charlottesville-cdnt1-bg8-11c-b-152.chvlva.adelphia.net] has quit [Ping timeout: 480 seconds] 03:46 < revenger> not in the kernel here 03:46 < revenger> ok.. in 2.6 it's there 03:46 < revenger> 32768 thanks so far! 03:47 < DrNick> that's the default for compatibility with old apps that expect pid_t to be a signed 16-bit integer 03:48 < revenger> 32768 is unsigned but why unsigned then? 03:48 < rene> then it would need to be 32767 03:48 < revenger> signed int was 65k even on my old 286pc 03:48 < revenger> unsigned* 03:48 < rene> 16-bit int = -32768 .. 32767 03:48 < revenger> signed was 32* 03:49 < revenger> -pids were allowed?! 03:49 < revenger> don't think so 03:49 < rene> nono 03:49 < rene> bu 32767 is therefore the maximum value you can represent in a 16bit int 03:50 < zinx> 16 bit signed int :/ 03:50 < rene> int in the C sense is signed 03:50 < revenger> but why 32768 -? 03:50 < rene> otherwise it's an unsigned int ;) 03:50 < revenger> better but why -32768 03:51 < revenger> why would you need signed int for pids? 03:51 < zinx> revenger: because 1 bit is the sign, and 0 doesn't need a sign 03:51 < revenger> just say pid 0 is an error everything else is valid 03:51 < zinx> revenger: so you don't need 0x8000 and 0x0000 to both be 0 03:51 < zinx> revenger: therefore, 0x8000 is -32768 03:52 < zinx> revenger: (-1 is 0xffff, aka 0 - 1) 03:52 < revenger> but why for pids?.. still not clear either a process is valid or not .. lets say invalid is 0 03:52 < rene> revenger: you wouldn't need a negative PID, but (apparently) a PID historically was just stored in a (signed) int, back in the days when 32767 processes was insanity 03:53 < revenger> so back then it was a quickndirty startover :-) 03:53 < rene> now, having a max of 32767 would allow for compatibility with programs that still expect that 03:53 < rene> (as to why it's 32768 and not 32767... bug, I guess) 03:53 < revenger> wonder what apps would require that limit .. opensource is known to be more flexible than closed source.. 03:54 < revenger> anyway my question is answered thanks so far! :-) now the bsd question how many pids are allowed there.. (I'll better ask that question in a bsd channel as well) 03:56 < rene> btw: Documentation/sysctl/kernel.txt:PIDs of value pid_max or larger are not allocated. 03:57 < rene> so just misnemd 03:57 < rene> *misnamed

Notizen

n elemente von from in den kernelspace kopieren:

copy_from_user(to, from, n);

API Changes Kernel 2.6.11:

remap_page_range() -> remap_pfn_range()

DMA Memory content/creative extigy 2 channels

-86 26 72 18 -95 21 36 14 -30 17 -116 11 -51 23 -108 18 109 22 96 18 -49 8 45 6 80 -2 24 -3 -89 -5 -118 -5 43 -2 -33 -2 -14 3 84 5 -116 2 91 4 35 -6 10 -4 -72 -9 -61 -7 14 -15 84 -13 -20 -16 7 -13 -33 -15 117 -13 105 -16 105 -15 72 -18 122 -18 123 -23 -84 -24 54 -26 -115 -28 -45 -28 -93 -30 -6 -31 89 -33 -80 -29 126 -32 19 -15 91 -19 86 2 27 -2 -7 10 -17 5 -70 8 -23 2 -114 11 113 5 -12 11 -74 5 14 11 -75 4 -39 15 -113 9 97 21 59 15 -106 23 106 17 58 25 -18 18 16 29 -23 22 -91 36 0 31 7 47 10 42 -99 58 -100 54 -80 66 61 64 43 63 73 62 -107 60 45 61 -77 57 0 60 35 47 81 51 76 32 90 38 80 21 86 29 94 17 -105 27 -108 15 3 28 85 10 -88 24 -19 7 -44 23 96 9 -106 26 -101 6 101 24 -85 6 91 24 82 4 -86 21 -29 -6 -93 11 114 -18 67 -2 31 -24 -28 -10 -107 -23 76 -9 43 -22 -99 -10 -38 -26 -77 -15 42 -25 95 -16 -46 -25 -95 -17 -1 -30 -94 -23 38 -21 47 -15 95 -10 -10 -4 0 -10 -10 -3 -107 -12 107 -2 119 -14 -81 -2 26 -19 11 -4 65 -28 -34 -11 -81 -34 -43 -14 24 -29 -56 -7 -86 -21 -47 4 -6 -21 43 7 -74 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10 -97 26 -25 12 30 29 16 16 80 32 -48 2 -14 -9 -64 -9 -41 -6 -86 -8 -82 -3 118 -7 63 4 -17 -3 108 11 30 4 101 13 113 5 -113 12 -117 3 -72 10 111 0 14 7 -58 -5 -110 3 -36 -9 -9 1 -97 -10 10 -5 72 -16 -115 -16 73 -26 -32 -23 98 -32 -16 -30 -38 -38 -46 -35 -89 -41 -38 -36 19 -39 91 -37 28 -38 -63 -42 -90 -41 -128 -47 53 -44 40 -51 117 -47 110 -54 31 -48 34 -52 115 -45 -87 -48 -12 -39 77 -47 91 -36 21 -45 44 -32 83 -46 -44 -32 26 -50 86 -35 -67 -48 97 -32 -9 -40 2 -23 69 -30 8 -13 111 -23 -124 -6 -82 -20 -124 -3 -89 -21 69 -4 4 -24 95 -8 -26 -27 92 -11 -49 -22 -65 -7 38 -17 -40 -2 -93 -20 -89 -4 23 -19 45 -4 124 -19 126 -5 -37 -21 -5 -9 78 -20 -94 -11 -50 -16 1 -9 9 -10 94 -7 118 -9 -86 -8 30 -10 -89 -11 -26 -10 67 -12 70 -10 -104 -15 93 -17 96 -23 50 -17 -21 -25 7 -12 -66 -21 39 -12 -120 -22 -101 -12 112 -22 -67 -10 69 -20 30 -7 127 -19 97 -5 -36 -18 -6 -4 -31 -16 -118 -4 -104 -15 23 -7 51 -17 -95 -14 97 -23 121 -19 31 -28 94 -21 0 -30 61 -24 -64 -34 37 -24 -10 -35 94 -23 9 -33 -107 -24 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-5 122 -10 126 -6 -101 -9 45 -5 72 -4 64 -1 18 1 125 3 -24 2 88 5 -50 2 59 6 43 3 83 7 77 5 17 9 39 8 63 11 -71 9 -111

C Format:

char foo[]={-86,26,72,18,-95,21,36,14,-30,17,-116,11,-51,23,-108,18,109,22,96,18,-49,8,45,6,80,-2,24,-3,-89,-5,-118,-5,43,-2,-33,-2,-14,3,84,5,-116,2,91,4,35,-6,10,-4,-72,-9,-61,-7,14,-15,84,-13,-20,-16,7,-13,-33,-15,117,-13,105,-16,105,-15,72,-18,122,-18,123,-23,-84,-24,54,-26,-115,-28,-45,-28,-93,-30,-6,-31,89,-33,-80,-29,126,-32,19,-15,91,-19,86,2,27,-2,-7,10,-17,5,-70,8,-23,2,-114,11,113,5,-12,11,-74,5,14,11,-75,4,-39,15,-113,9,97,21,59,15,-106,23,106,17,58,25,-18,18,16,29,-23,22,-91,36,0,31,7,47,10,42,-99,58,-100,54,-80,66,61,64,43,63,73,62,-107,60,45,61,-77,57,0,60,35,47,81,51,76,32,90,38,80,21,86,29,94,17,-105,27,-108,15,3,28,85,10,-88,24,-19,7,-44,23,96,9,-106,26,-101,6,101,24,-85,6,91,24,82,4,-86,21,-29,-6,-93,11,114,-18,67,-2,31,-24,-28,-10,-107,-23,76,-9,43,-22,-99,-10,-38,-26,-77,-15,42,-25,95,-16,-46,-25,-95,-17,-1,-30,-94,-23,38,-21,47,-15,95,-10,-10,-4,0,-10,-10,-3,-107,-12,107,-2,119,-14,-81,-2,26,-19,11,-4,65,-28,-34,-11,-81,-34,-43,-14,24,-29,-56,-7,-86,-21,-47,4,-6,-21,43,7,-74,-20,114,9,71,-40,-15,-6,-16,-9,-18,111,-19,47,-20,42,-22,56,-16,22,-18,88,-8,59,-10,43,0,4,-2,55,6,-110,3,37,10,119,6,-9,10,19,6,-92,8,-46,2,80,6,20,0,-88,7,-64,1,-73,9,124,4,-73,9,-18,4,19,10,68,5,-85,7,22,2,-53,1,43,-5,81,-1,-79,-9,1,4,-118,-5,35,11,39,2,-6,14,-73,5,-110,15,10,6,47,16,94,6,-18,17,-53,7,-76,20,37,10,88,23,-125,12,-29,25,-81,14,18,28,121,16,19,27,39,15,71,24,-35,11,70,23,81,10,10,25,115,11,110,28,13,14,127,31,69,16,-18,31,-13,15,28,29,-116,12,-54,26,41,10,-88,27,107,11,38,29,-75,13,103,30,73,16,89,30,-49,17,74,26,-75,15,123,19,85,11,-40,13,110,8,-126,11,-25,8,-40,11,-72,11,125,13,10,15,60,15,-119,17,-76,14,-25,16,78,9,-77,10,-36,3,120,4,91,4,80,4,-85,5,1,5,46,6,-31,4,-93,6,101,4,-74,4,81,1,91,0,-56,-5,-29,-5,58,-10,87,-8,-53,-15,-6,-11,-83,-18,27,-9,-68,-18,-106,-7,-61,-17,-86,-9,7,-20,-21,-11,55,-24,8,-6,-80,-22,70,1,-68,-16,-25,6,-98,-11,15,9,81,-9,-85,8,94,-10,-66,6,-76,-13,77,4,118,-16,-95,3,-1,-18,41,7,-4,-15,110,14,41,-7,-106,21,100,0,69,22,95,1,20,19,116,-2,121,19,7,-1,112,23,65,3,-107,2,42,1,82,1,-20,3,19,4,-119,-5,-19,-5,94,-11,29,-10,120,-10,-58,-9,-22,-11,73,-8,-120,-16,-118,-12,36,-19,12,-13,118,-17,22,-9,-87,-16,118,-7,-3,-23,43,-13,-51,-31,95,-22,59,-28,73,-21,95,-18,-105,-13,100,-14,32,-10,92,-16,44,-13,-69,-16,59,-13,82,-16,38,-13,-22,-25,-116,-21,121,-35,13,-30,-21,-38,73,-32,7,-34,-29,-29,-101,-36,-120,-30,-29,-42,46,-36,127,-42,71,-38,24,-36,-59,-35,115,-38,-12,-39,-109,-44,41,-46,-52,-44,-33,-48,-58,-41,-11,-46,-92,-43,-114,-48,-5,-49,-6,-54,63,-50,86,-55,20,-46,20,-51,80,-43,-13,-49,124,-44,89,-50,-42,-44,-122,-51,36,-36,-108,-45,123,-32,3,-41,-73,-35,-99,-45,8,-31,91,-42,-55,-23,-102,-34,72,-16,-60,-28,-87,-16,8,-27,13,-19,-105,-31,126,-21,-104,-32,-62,-19,-61,-29,-68,-19,-108,-28,-94,-21,-89,-30,75,-17,-115,-27,52,-11,-5,-23,64,-10,71,-23,-32,-14,101,-28,103,-12,40,-27,68,-4,49,-19,72,3,0,-11,18,6,-63,-8,-79,6,63,-6,46,7,118,-5,-26,5,-76,-6,62,0,69,-11,-52,-3,-50,-14,-43,7,-60,-4,78,16,-6,4,112,18,111,6,-97,20,-71,7,-63,23,42,10,-97,26,-25,12,30,29,16,16,80,32,-48,2,-14,-9,-64,-9,-41,-6,-86,-8,-82,-3,118,-7,63,4,-17,-3,108,11,30,4,101,13,113,5,-113,12,-117,3,-72,10,111,0,14,7,-58,-5,-110,3,-36,-9,-9,1,-97,-10,10,-5,72,-16,-115,-16,73,-26,-32,-23,98,-32,-16,-30,-38,-38,-46,-35,-89,-41,-38,-36,19,-39,91,-37,28,-38,-63,-42,-90,-41,-128,-47,53,-44,40,-51,117,-47,110,-54,31,-48,34,-52,115,-45,-87,-48,-12,-39,77,-47,91,-36,21,-45,44,-32,83,-46,-44,-32,26,-50,86,-35,-67,-48,97,-32,-9,-40,2,-23,69,-30,8,-13,111,-23,-124,-6,-82,-20,-124,-3,-89,-21,69,-4,4,-24,95,-8,-26,-27,92,-11,-49,-22,-65,-7,38,-17,-40,-2,-93,-20,-89,-4,23,-19,45,-4,124,-19,126,-5,-37,-21,-5,-9,78,-20,-94,-11,-50,-16,1,-9,9,-10,94,-7,118,-9,-86,-8,30,-10,-89,-11,-26,-10,67,-12,70,-10,-104,-15,93,-17,96,-23,50,-17,-21,-25,7,-12,-66,-21,39,-12,-120,-22,-101,-12,112,-22,-67,-10,69,-20,30,-7,127,-19,97,-5,-36,-18,-6,-4,-31,-16,-118,-4,-104,-15,23,-7,51,-17,-95,-14,97,-23,121,-19,31,-28,94,-21,0,-30,61,-24,-64,-34,37,-24,-10,-35,94,-23,9,-33,-107,-24,-93,-34,53,-27,42,-37,126,-33,11,-43,-17,-37,-68,-47,72,0,9,12,107,-1,-37,11,85,-3,5,10,-53,-8,-58,5,-13,-7,-108,7,-117,-5,13,10,-9,-6,38,10,117,-5,-103,10,-116,-5,-74,9,73,-8,-50,4,-39,-9,-94,2,15,-6,-120,3,-38,-5,-114,4,-63,1,-35,9,27,4,68,11,28,7,-29,12,-50,10,30,15,127,12,-53,15,0,15,3,18,-44,18,42,22,-51,23,-96,27,98,29,91,33,-75,31,75,35,-20,29,-51,32,14,30,74,32,-60,27,-81,29,83,25,13,27,93,23,-125,24,-88,17,-119,17,-105,11,-97,9,48,6,61,2,-56,2,59,-3,-92,3,36,-3,-70,7,-38,0,-108,10,-102,3,74,10,60,3,41,7,19,0,-61,3,3,-3,-29,2,67,-3,25,3,66,-1,-24,5,-1,3,11,10,-81,9,5,12,-108,12,98,12,107,13,71,12,-44,13,-2,11,-121,14,-113,12,-100,16,-98,13,81,19,-121,9,90,16,51,1,33,8,-100,-6,-119,0,55,-12,-126,-8,112,-17,-1,-15,-63,-21,-87,-20,80,-23,-125,-24,-95,-24,-29,-27,34,-25,63,-30,-89,-29,-64,-36,-101,-32,75,-40,-63,-33,-5,-42,-113,-33,51,-41,58,-34,-91,-42,-69,-36,-89,-43,-89,-35,112,-42,-20,-36,63,-43,5,-36,16,-44,-89,-34,-9,-42,71,-30,106,-37,-51,-27,6,-32,-86,-22,-17,-27,-31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Datei im Kernelmodus öffnen und beschreiben(dateirechte müssen beachtet werden!):

mm_segment_t fs; fs = get_fs(); set_fs (KERNEL_DS);//get_ds()); pr_file = filp_open("/var/log/usb.log",O_RDWR|O_CREAT|O_APPEND,600); if (IS_ERR(pr_file)){ printk("error unable to create /var/log/usb.log\n"); } else { pr_file->f_op->write(pr_file, "foo", 3, &pr_file->f_pos); filp_close(pr_file,NULL); }

Linux DMA

http://www.linux-magazin.de/Service/Books/Buecher/HW-Treiber/memdma.html

Wenn alles zusammenkommt und auf einmal Sinn ergibt

Mit einer standard Debian kann man so ca 375 Threads erstellen. Woher kommt die Limitierung aber? Ziemlich einfach, der Kernel hat eine Aufteilung von 3:1 unter Linux (BSD und Windows sind häufig 2:2) das heißt von 4 GB physikalischen RAM können maximal 3 GB von einem Prozess verwendet werden. Teilt man jetzt 3 GB / die definierte Stack größe erhält man die Limitierung der Threads auf dem System. Die Größe der Stacksize wird in der limits.conf unter /etc/security festgelegt(das ganze muss auch mittels PAM erlaubt sein), sie kann jedoch auch "OnTheFly?" mittels ulimit -s geändert werden. Bei mysql ist zum Beispiel eine Größe von 128kbyte sinnvoll(laut Doku) was wiederum eine sehr hohe Anzahl von Verbindungen erlaubt.

Diskussion die mich dazu angeregt hat:

However, I was most amazed to see that the limit on stack size on FreeBSD (5.3 Release) was 64M by default! I was just wondering, how is FreeBSD able to create about a 1000 threads with that kind of a stack limit. Also, is there anything specific in its implementation which makes it difficult to incorporate in Linux? Wouldn't it be a good idea to remove this "trade-off" between stack limit and number of threads and fail thread creation only when we have run out of address space being *actually used* in the stacks in a process.

Antwort

On FreeBSD the default thread stack size is not computed from ulimit -s, but is constant. They apparently only recently increased it to 1MB (resp. 2MB on 64-bit arches), from 64K. On Linux, the default thread stack size (except with fixed stack LinuxThreads) is determined from ulimit -s (with a constant default if ulimit -s is unlimited). If your threaded application has specific needs for stack sizes, it can always pthread_attr_setstacksize to whatever you find appropriate. The thread library needs to know the stack size limit before creating the thread, that can't be changed dynamically.

Quelle: linux-kernel@vger.kernel.org (mailinglist)

Linked Lists im Kernel

struct foobar{ int a; int b; struct list_head list; }; struct foobar testlist; struct foobar *tmp; struct list_head *pos, *q; INIT_LIST_HEAD(&testlist.list); tmp=(struct foobar*)malloc(sizeof(struct foobar)); tmp->a=1; tmp->b=2; list_add(&(tmp->list),&(testlist.list)); // fügt das element hinzu list_for_each(pos, &testlist.list){ tmp = list_entry(pos,struct foobar, list); // define printf("%d\n",tmp->a); } // alles in einem list_for_each_entry(tmp,&foobar.list,list){ printf("%d\n",tmp->a); } list_for_each_safe(pos,q,&foobar.list){ tmp=list_entry(pos,struct foobar, list); list_del(pos); free(tmp); }

Memory Mapped IO

http://www.kernelnewbies.org/documents/kdoc/deviceiobook/mmio.html

http://www.oreilly.de/german/freebooks/linuxdrive2ger/memmap.html

dev->frame[i].bufmem; (void*) vmalloc_to_pfn Map a vmalloc()-space virtual address to the physical page frame number. remap_pfn_range

Kernelmodule

Aufbau:

Module verwenden das ELF Binärformat das mit einigen zusätzlichen Sektionen versehen ist.

__ksymtab und __ksymtab_gpl .. enthalten eine Symboltabelle mit allen Symbolen die vom Modul exportiert werden.

__kcrctab und __kcrctab_gpl enthalten Checksummen für alle GPL- exportierten Funktionen des Moduls.

in __versions befinden sich die checksummen für alle Referenzen die das modul aus externen Quellen verwendet. (diese sektionen werden nur angelegt wenn das versionskontroll feature bei der konfiguration des kerns aktiviert wurde.

__param speichert die informationen darüber, mit welchen Parametern ein Modul versorgt werden kann.

in .modinfo stehen die abhängigkeiten des jeweiligen moduls

Dummy modul

hello.c:

#include <linux/module.h #include <linux/kernel.h> #include <linux/fs.h> static int dev_open(struct inode *inode, struct file *file){ printk("device opened!\n"); return(0); } static ssize_t dev_read(struct file *file, char __user * buffer, size_t length, loff_t *offset){ printk("device opened!\n"); return(0); } struct file_operations fops = { .read = dev_read, .open = dev_open, }; static int __init hello_main(void) { register_chrdev(185,"test",&fops); return 0; } static void __exit hello_exit(void) { unregister_chrdev(185,"test"); } module_init(hello_main); module_exit(hello_exit);

test erscheint dann in /proc/devices

Makefile

obj-m += hello.o #hello-objs = hello.o #additional objects here KERNEL_VERSION = $(shell uname -r) KERNEL_DIR = /lib/modules/$(KERNEL_VERSION)/build default: $(MAKE) -C $(KERNEL_DIR) SUBDIRS=$(PWD) modules

Doku: <linuxkernel>Documentation/kbuild/makefiles.txt und modules.txt

Locking Mechanismen

 * Atomare Operationen

 * Semaphore

will während der erste prozess sich im down segment befindet ein weiterer prozess den kritischen code betreten wird er vom kernel sozusagen schlafengelegt solange bis der erste prozess wieder die up funktion aufgerufen hat (welche den wert der semaphore wieder auf 1 erhöht und einen schlafenden prozess aus einer queue auswählt, welcher dann die down funktion weiter ausführt und die semaphore wieder auf 0 setzt)

 * und Spinlocks,

01:37 < revenger> what are these flags for in for example spinlock_irqsave? the first one is clear the spinlock struct.. but the second one? 01:37 -!- santamarta [~Juanjo@195.Red-213-96-224.pooles.rima-tde.net] has quit [Remote host closed the connection] 01:38 < conman> save the state of the irqs and return it back after unlock ? 01:38 < revenger> well what's meant with state? what state? 01:39 < conman> enable/disabled irqs 01:39 < revenger> ah ok! 01:39 < revenger> thanks

debugging

die ersten 3 zeichen werden von syslog weggeschnitten sofern das kommentar eines von folgenden tags am anfang enthält:

 <0> System is not usable
 <1> kern alert
 <2> critical system
 <3> errors occured
 <4> warning
 <5> notice
 <6> information
 <7> debug info

 {WARN ON}?(index==limit); -- gibt ein warning/zeilennummer und einen traceback aus an dieser stelle
 {BUG ON}?(foo==bar); -- das selbe wie {WARN ON}? nur der codeblock wird auch verlassen

#if 0 ... ... #endif

license fun

MODULE_LICENSE("GPL\0for files in the \"GPL\" directory; for others, only LICENSE file applies");

no description .. just funny

modinfo

macros defined in the module

MODULE_LICENSE("GPL"); MODULE_AUTHOR("Markus Rechberger"); MODULE_DESCRIPTION("just a module template");

modinfo test.ko filename: test.ko license: GPL author: Markus Rechberger description: just a module template vermagic: 2.6.11.5 preempt PENTIUMM gcc-3.3

copy_to_user

der rückgabewert ist die anzahl bytes die nicht kopiert werden konnte

interrupt service routinen

es gibt davon nur 16 (siehe z.b xosview 0-15), Registrierung von Isrs kommt noch..

datenablage im speicher

Daten werden meist alligned in den speicher abgelegt

z.b

struct foobar { __u8 a; __u8 b; __s32 c; };

wenn der speicher bei 0xbffffa8c anfängt würde der block für __s32 c; bei addresse 0xbfffa8e beginnen, da diese adresse aber nicht durch 4 teilbar ist werden diese 2 bytes aus performancegründen "verschenkt". Will man die daten explizit gepackt angeben muss man am ende des structs noch __attribute__ packet; einfügen

TSC

02:27 < revenger> any idea what cpu_has_tsc stands for? (tsc actually)? 02:28 < bob2> it's a timer thing 02:28 < bob2> google says www.kernelhacking.org/docs/kernelhacking-HOWTO/indexs17.html 02:28 < revenger> right I got a book (kernel device drivers) but it doesn't explain what tsc is for.. 02:28 < revenger> is/stands for 02:29 < revenger> time stamp counter ah 02:29 < revenger> thanks again

VMA

If a page needs to be aligned on a page boundary, {PAGE ALIGN}?() is used.

/* to align the pointer to the (next) page boundary */ #define PAGE_ALIGN(addr) (((addr) + PAGE_SIZE - 1) & PAGE_MASK)

>The PAGE_MASK macro is defined as > >/* PAGE_SHIFT determines the page size */ >#define PAGE_SHIFT 12 >#define PAGE_SIZE (1UL << PAGE_SHIFT) >#define PAGE_MASK (~(PAGE_SIZE-1)) > >in /linux/include/asm-i386/page.h > >and the macro usage is like > >pos=filp->f_pos; >ppos=pos&PAGE_MASK ppos will result something like the offset from the start of a page. It will mean how much pos is disaligned by the 4k boundaries.

graphical overview: http://i30www.ira.uka.de/teaching/coursedocuments/106/03-06_Kernallokation-und-Mapping_Meinhardt.pdf

regarding linus, don't use vmalloc -> it's slow, everything's explained in that pdf so far..

11:31 < revenger_> hmm.. #define PAGE_ALIGN(addr) (((addr) + PAGE_SIZE - 1) & PAGE_MASK) 11:31 < revenger_> don't really understand that now.. 11:53 < da-x> PAGE_ALIGN(addr) = returns the 'end' page address of an 'end' address. 11:53 < da-x> which is a quite cryptic description. 11:56 < da-x> suppose you have a buffer with an address X and size Y bytes. PAGE_ALIGN(X+Y) will return the first page which *doesn't* overlap with the buffer. 11:57 < da-x> which can be useful at times. 12:00 < da-x> a better description would be 'align to the next page if not already aligned'.

Einfach erklärt:

{PAGE ALIGN}? Beispiel:

int b=55; b=PAGE_ALIGN(b);

b entspricht dann 4096 bytes

int b=5555; b=PAGE_ALIGN(b);

b entspricht dann 8192 bytes

http://www.xtrj.org/ppc/ powerpc and linux inside..

hier nochmal linux device drivers online (already ordered that book as well)

http://www.xml.com/ldd/chapter/book/

Sequence Files/Proc filesystem

descrpition about sequence files on lwn.net (english) also includes a discussion

  https://lwn.net/Articles/22355/

  http://ezs.kr.hsnr.de/TreiberBuch/html/sec.proc01.html

Neues Geräte Modell (/sys/)

Das Gerätemodell bildet ab, wie die Prozessoren eines Systems mit seinen Controller-Bausteinen und diese wiederum mit den Peripheriekarten und mit sonstiger Hardware zusammenhängen. Eine detailierte Beschreibung gibts wiedermal in den Treiberbüchern..

z.b neue Bussysteme anlegen

static struct bus_type can = { .name = "CAN", }; drvinit(){ bus_register(&can); } drvexit(){ bus_unregister(&can); }

devfs

bereits in 2.6 als depreciated gekennzeichnet, da es angeblich race conditions enthält sowie z.b auch die zugriffsregelung nicht ordentlich implementiert ist (broken by design) ansonsten siehe devfs_mk_cdev, devfs_remove und devfs_mk_symlink

Module parametrieren

In Kernel 2.6 wurde das Makro {MODULE PARM}? durch drei neue Makros ersetzt: module_param, module_param_array und module_param_string.

Example (also includes a sysfs example):

#include <linux/fs.h> #include <linux/module.h> #include <linux/init.h> #include <linux/device.h> #define DRIVER_MAJOR 240 MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("Another sample module."); MODULE_AUTHOR("Markus Rechberger"); static int exampleparam = 0; //MODULE_PARM(exampleparam, "i"); or following line, the last argument is responsible for permissions module_param(exampleparam,int,0); MODULE_PARM_DESC(exampleparam, " sample desc, integer value(1-10)"); static struct file_operations fops; static DECLARE_COMPLETION (dev_obj_is_free); static int frequenz; // Zustandsvariable des Gerätes static void mydevice_release( struct device *dev){ complete(&dev_obj_is_free); } struct platform_device mydevice ={ .name ="MyDevice", .id = 0, .dev = { .release = mydevice_release, } }; static struct device_driver mydriver ={ .name = "MyDevDrv", .bus = &platform_bus_type, }; static ssize_t read_freq (struct device *dev, char *buf){ snprintf(buf,256,"frequenz: %d",frequenz); return strlen(buf)+1; } static ssize_t write_freq (struct device *dev,const char *buf, size_t count){ frequenz=simple_strtoul(buf, NULL, 0); return strlen(buf)+1; } static DEVICE_ATTR(freq, S_IRUGO|S_IWUGO, read_freq, write_freq); static int __init drv_init(void){ printk("example param: %d\n",exampleparam); if(register_chrdev(DRIVER_MAJOR,"MyDevice",&fops)==0){ driver_register(&mydriver); platform_device_register(&mydevice); mydevice.dev.driver = &mydriver; device_bind_driver(&mydevice.dev); device_create_file(&mydevice.dev,&dev_attr_freq); return 0; } return -EIO; } static void __exit drv_exit(void){ device_remove_file(&mydevice.dev,&dev_attr_freq); device_release_driver(&mydevice.dev); platform_device_unregister(&mydevice); driver_unregister(&mydriver); unregister_chrdev(DRIVER_MAJOR, "MyDevice"); wait_for_completion(&dev_obj_is_free); } module_init(drv_init); module_exit(drv_exit);

debian:/devel/kernel/example15# modinfo main.ko filename: main.ko license: GPL description: Another sample module. author: Markus Rechberger vermagic: 2.6.11.5 preempt PENTIUMM gcc-3.3 depends: parm: exampleparam: sample desc, integer value(1-10)

available datatypes:

type desc short signed short ushort unsigned short int signed int uint unsigned int long signed long ulong unsigned long charp string bool bool invbool inverted bool

HZ

#ifdef __KERNEL__ # define HZ 1000 /* Internal kernel timer frequency */ # define USER_HZ 100 /* .. some user interfaces are in "ticks" */ # define CLOCKS_PER_SEC (USER_HZ) /* like times() */ #endif

# export ... declare -x HOME="/root" declare -x HUSHLOGIN="FALSE" declare -x HZ="100" ...

so in the kernel HZ is set to 1000 which stands for 1 second, for applications it's set to 100

20:35 < rene> revenger_: the HZ environment variable isn't directly set by the kernel. It's set from the ENV_HZ value in /etc/login/defs (if present). Yes, it is supposed to be the kernel HZ and as such, 100 is stil correct, asthe kernel internal HZ and what is presented to userspace are decoupled -- userspace is always supposed to see 100 20:39 < rene> revenger_: (/etc/login.defs)

memory allocation

SetPageReserved?() wird benutzt um Speicher zu markieren der nicht ausgelagert werden soll

RingQueue?

here's an example of a ringqueue (usbvideo.c), the depreciated function wait_on is used in that driver as well, below the main functions which also get exported in the kernel.

#define RING_QUEUE_SIZE (128*1024) /* Must be a power of 2 */ #define RING_QUEUE_ADVANCE_INDEX(rq,ind,n) (rq)->ind = ((rq)->ind + (n)) & ((rq)->length-1) #define RING_QUEUE_DEQUEUE_BYTES(rq,n) RING_QUEUE_ADVANCE_INDEX(rq,ri,n) #define RING_QUEUE_PEEK(rq,ofs) ((rq)->queue[((ofs) + (rq)->ri) & ((rq)->length-1)]) struct RingQueue { unsigned char *queue; /* Data from the Isoc data pump */ int length; /* How many bytes allocated for the queue */ int wi; /* That's where we write */ int ri; /* Read from here until you hit write index */ wait_queue_head_t wqh; /* Processes waiting */ };

static void RingQueue_Initialize(struct RingQueue *rq) { assert(rq != NULL); init_waitqueue_head(&rq->wqh); } static void *usbvideo_rvmalloc(unsigned long size) { void *mem; unsigned long adr; size = PAGE_ALIGN(size); // padding up to a full page size (for example if size is 234 size will get padded up to 4096 mem = vmalloc_32(size); if (!mem) return NULL; memset(mem, 0, size); /* Clear the ram out, no junk to the user -- also security issue, passwords might be in that memoryjunk worst case */ adr = (unsigned long) mem; while (size > 0) { SetPageReserved(vmalloc_to_page((void *)adr)); // pin them in memory (no swapping out for these addresses) adr += PAGE_SIZE; size -= PAGE_SIZE; } return mem; } static void RingQueue_Allocate(struct RingQueue *rq, int rqLen) { /* Make sure the requested size is a power of 2 and round up if necessary. This allows index wrapping using masks rather than modulo */ int i = 1; assert(rq != NULL); assert(rqLen > 0); while(rqLen >> i) i++; if(rqLen != 1 << (i-1)) rqLen = 1 << i; rq->length = rqLen; rq->ri = rq->wi = 0; // read index = write index = 0 rq->queue = usbvideo_rvmalloc(rq->length); assert(rq->queue != NULL); } int RingQueue_Enqueue(struct RingQueue *rq, const unsigned char *cdata, int n) { int enqueued = 0; assert(rq != NULL); assert(cdata != NULL); assert(rq->length > 0); while (n > 0) { int m, q_avail; /* Calculate the largest chunk that fits the tail of the ring */ q_avail = rq->length - rq->wi; if (q_avail <= 0) { rq->wi = 0; q_avail = rq->length; } m = n; assert(q_avail > 0); if (m > q_avail) m = q_avail; memcpy(rq->queue + rq->wi, cdata, m); RING_QUEUE_ADVANCE_INDEX(rq, wi, m); cdata += m; enqueued += m; n -= m; } return enqueued; } int RingQueue_Dequeue(struct RingQueue *rq, unsigned char *dst, int len) { int rql, toread; assert(rq != NULL); assert(dst != NULL); rql = RingQueue_GetLength(rq); if(!rql) return 0; /* Clip requested length to available data */ if(len > rql) len = rql; toread = len; if(rq->ri > rq->wi) { /* Read data from tail */ int read = (toread < (rq->length - rq->ri)) ? toread : rq->length - rq->ri; memcpy(dst, rq->queue + rq->ri, read); toread -= read; dst += read; rq->ri = (rq->ri + read) & (rq->length-1); } if(toread) { /* Read data from head */ memcpy(dst, rq->queue + rq->ri, toread); rq->ri = (rq->ri + toread) & (rq->length-1); } return len; } static void RingQueue_InterruptibleSleepOn(struct RingQueue *rq) { assert(rq != NULL); interruptible_sleep_on(&rq->wqh); } void RingQueue_WakeUpInterruptible(struct RingQueue *rq) { assert(rq != NULL); if (waitqueue_active(&rq->wqh)) wake_up_interruptible(&rq->wqh); } void RingQueue_Flush(struct RingQueue *rq) { assert(rq != NULL); rq->ri = 0; rq->wi = 0; }

RingQueue? Test im Userspace:

Values: 134515731 - 6 - 0 enqueued: 6 Markus Values: 134515731 - 6 - 0 enqueued: 6 Markus Values: 134515731 - 6 - 0 enqueued: 6 Markus Values: 134515731 - 6 - 0 enqueued: 6 Markus Queue: Mark //queuecontent 4 chars Values: 134515768 - 11 - 0 Rechberger Queue: usMarkusMarkusMarkusRechberger //queuecontent the rest

Linux DMA

http://www.linuxjournal.com/article/1222

also isa ist limitiert auf die ersten 16 MB Ram für DMA transfers

IO

the first parallel port starts at 0x378, the second one is 0x278 there are 12 output pins and 5 input pins (rest is grounding)

Mutexes over Semaphores

recently many drivers got patched to use mutexes instead of semaphores, the reason behind that action - mutexes are supposed to be faster - https://lwn.net/Articles/165039/