diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/proc.txt | 2 | ||||
| -rw-r--r-- | Documentation/hwmon/amc6821 | 102 | ||||
| -rw-r--r-- | Documentation/ioctl/ioctl-number.txt | 203 | ||||
| -rw-r--r-- | Documentation/kernel-doc-nano-HOWTO.txt | 12 | ||||
| -rw-r--r-- | Documentation/trace/ring-buffer-design.txt | 56 |
5 files changed, 296 insertions, 79 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 220cc6376ef8..0d07513a67a6 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -177,7 +177,6 @@ read the file /proc/PID/status: CapBnd: ffffffffffffffff voluntary_ctxt_switches: 0 nonvoluntary_ctxt_switches: 1 - Stack usage: 12 kB This shows you nearly the same information you would get if you viewed it with the ps command. In fact, ps uses the proc file system to obtain its @@ -231,7 +230,6 @@ Table 1-2: Contents of the statm files (as of 2.6.30-rc7) Mems_allowed_list Same as previous, but in "list format" voluntary_ctxt_switches number of voluntary context switches nonvoluntary_ctxt_switches number of non voluntary context switches - Stack usage: stack usage high water mark (round up to page size) .............................................................................. Table 1-3: Contents of the statm files (as of 2.6.8-rc3) diff --git a/Documentation/hwmon/amc6821 b/Documentation/hwmon/amc6821 new file mode 100644 index 000000000000..ced8359c50f8 --- /dev/null +++ b/Documentation/hwmon/amc6821 @@ -0,0 +1,102 @@ +Kernel driver amc6821 +===================== + +Supported chips: + Texas Instruments AMC6821 + Prefix: 'amc6821' + Addresses scanned: 0x18, 0x19, 0x1a, 0x2c, 0x2d, 0x2e, 0x4c, 0x4d, 0x4e + Datasheet: http://focus.ti.com/docs/prod/folders/print/amc6821.html + +Authors: + Tomaz Mertelj <tomaz.mertelj@guest.arnes.si> + + +Description +----------- + +This driver implements support for the Texas Instruments amc6821 chip. +The chip has one on-chip and one remote temperature sensor and one pwm fan +regulator. +The pwm can be controlled either from software or automatically. + +The driver provides the following sensor accesses in sysfs: + +temp1_input ro on-chip temperature +temp1_min rw " +temp1_max rw " +temp1_crit rw " +temp1_min_alarm ro " +temp1_max_alarm ro " +temp1_crit_alarm ro " + +temp2_input ro remote temperature +temp2_min rw " +temp2_max rw " +temp2_crit rw " +temp2_min_alarm ro " +temp2_max_alarm ro " +temp2_crit_alarm ro " +temp2_fault ro " + +fan1_input ro tachometer speed +fan1_min rw " +fan1_max rw " +fan1_fault ro " +fan1_div rw Fan divisor can be either 2 or 4. + +pwm1 rw pwm1 +pwm1_enable rw regulator mode, 1=open loop, 2=fan controlled + by remote temperature, 3=fan controlled by + combination of the on-chip temperature and + remote-sensor temperature, +pwm1_auto_channels_temp ro 1 if pwm_enable==2, 3 if pwm_enable==3 +pwm1_auto_point1_pwm ro Hardwired to 0, shared for both + temperature channels. +pwm1_auto_point2_pwm rw This value is shared for both temperature + channels. +pwm1_auto_point3_pwm rw Hardwired to 255, shared for both + temperature channels. + +temp1_auto_point1_temp ro Hardwired to temp2_auto_point1_temp + which is rw. Below this temperature fan stops. +temp1_auto_point2_temp rw The low-temperature limit of the proportional + range. Below this temperature + pwm1 = pwm1_auto_point2_pwm. It can go from + 0 degree C to 124 degree C in steps of + 4 degree C. Read it out after writing to get + the actual value. +temp1_auto_point3_temp rw Above this temperature fan runs at maximum + speed. It can go from temp1_auto_point2_temp. + It can only have certain discrete values + which depend on temp1_auto_point2_temp and + pwm1_auto_point2_pwm. Read it out after + writing to get the actual value. + +temp2_auto_point1_temp rw Must be between 0 degree C and 63 degree C and + it defines the passive cooling temperature. + Below this temperature the fan stops in + the closed loop mode. +temp2_auto_point2_temp rw The low-temperature limit of the proportional + range. Below this temperature + pwm1 = pwm1_auto_point2_pwm. It can go from + 0 degree C to 124 degree C in steps + of 4 degree C. + +temp2_auto_point3_temp rw Above this temperature fan runs at maximum + speed. It can only have certain discrete + values which depend on temp2_auto_point2_temp + and pwm1_auto_point2_pwm. Read it out after + writing to get actual value. + + +Module parameters +----------------- + +If your board has a BIOS that initializes the amc6821 correctly, you should +load the module with: init=0. + +If your board BIOS doesn't initialize the chip, or you want +different settings, you can set the following parameters: +init=1, +pwminv: 0 default pwm output, 1 inverts pwm output. + diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt index 947374977ca5..35cf64d4436d 100644 --- a/Documentation/ioctl/ioctl-number.txt +++ b/Documentation/ioctl/ioctl-number.txt @@ -56,10 +56,11 @@ Following this convention is good because: (5) When following the convention, the driver code can use generic code to copy the parameters between user and kernel space. -This table lists ioctls visible from user land for Linux/i386. It contains -most drivers up to 2.3.14, but I know I am missing some. +This table lists ioctls visible from user land for Linux/x86. It contains +most drivers up to 2.6.31, but I know I am missing some. There has been +no attempt to list non-X86 architectures or ioctls from drivers/staging/. -Code Seq# Include File Comments +Code Seq#(hex) Include File Comments ======================================================== 0x00 00-1F linux/fs.h conflict! 0x00 00-1F scsi/scsi_ioctl.h conflict! @@ -69,119 +70,228 @@ Code Seq# Include File Comments 0x03 all linux/hdreg.h 0x04 D2-DC linux/umsdos_fs.h Dead since 2.6.11, but don't reuse these. 0x06 all linux/lp.h -0x09 all linux/md.h +0x09 all linux/raid/md_u.h +0x10 00-0F drivers/char/s390/vmcp.h 0x12 all linux/fs.h linux/blkpg.h 0x1b all InfiniBand Subsystem <http://www.openib.org/> 0x20 all drivers/cdrom/cm206.h 0x22 all scsi/sg.h '#' 00-3F IEEE 1394 Subsystem Block for the entire subsystem +'$' 00-0F linux/perf_counter.h, linux/perf_event.h '1' 00-1F <linux/timepps.h> PPS kit from Ulrich Windl <ftp://ftp.de.kernel.org/pub/linux/daemons/ntp/PPS/> +'2' 01-04 linux/i2o.h +'3' 00-0F drivers/s390/char/raw3270.h conflict! +'3' 00-1F linux/suspend_ioctls.h conflict! + and kernel/power/user.c '8' all SNP8023 advanced NIC card <mailto:mcr@solidum.com> -'A' 00-1F linux/apm_bios.h +'@' 00-0F linux/radeonfb.h conflict! +'@' 00-0F drivers/video/aty/aty128fb.c conflict! +'A' 00-1F linux/apm_bios.h conflict! +'A' 00-0F linux/agpgart.h conflict! + and drivers/char/agp/compat_ioctl.h +'A' 00-7F sound/asound.h conflict! +'B' 00-1F linux/cciss_ioctl.h conflict! +'B' 00-0F include/linux/pmu.h conflict! 'B' C0-FF advanced bbus <mailto:maassen@uni-freiburg.de> -'C' all linux/soundcard.h +'C' all linux/soundcard.h conflict! +'C' 01-2F linux/capi.h conflict! +'C' F0-FF drivers/net/wan/cosa.h conflict! 'D' all arch/s390/include/asm/dasd.h -'E' all linux/input.h -'F' all linux/fb.h -'H' all linux/hiddev.h -'I' all linux/isdn.h +'D' 40-5F drivers/scsi/dpt/dtpi_ioctl.h +'D' 05 drivers/scsi/pmcraid.h +'E' all linux/input.h conflict! +'E' 00-0F xen/evtchn.h conflict! +'F' all linux/fb.h conflict! +'F' 01-02 drivers/scsi/pmcraid.h conflict! +'F' 20 drivers/video/fsl-diu-fb.h conflict! +'F' 20 drivers/video/intelfb/intelfb.h conflict! +'F' 20 linux/ivtvfb.h conflict! +'F' 20 linux/matroxfb.h conflict! +'F' 20 drivers/video/aty/atyfb_base.c conflict! +'F' 00-0F video/da8xx-fb.h conflict! +'F' 80-8F linux/arcfb.h conflict! +'F' DD video/sstfb.h conflict! +'G' 00-3F drivers/misc/sgi-gru/grulib.h conflict! +'G' 00-0F linux/gigaset_dev.h conflict! +'H' 00-7F linux/hiddev.h conflict! +'H' 00-0F linux/hidraw.h conflict! +'H' 00-0F sound/asound.h conflict! +'H' 20-40 sound/asound_fm.h conflict! +'H' 80-8F sound/sfnt_info.h conflict! +'H' 10-8F sound/emu10k1.h conflict! +'H' 10-1F sound/sb16_csp.h conflict! +'H' 10-1F sound/hda_hwdep.h conflict! +'H' 40-4F sound/hdspm.h conflict! +'H' 40-4F sound/hdsp.h conflict! +'H' 90 sound/usb/usx2y/usb_stream.h +'H' C0-F0 net/bluetooth/hci.h conflict! +'H' C0-DF net/bluetooth/hidp/hidp.h conflict! +'H' C0-DF net/bluetooth/cmtp/cmtp.h conflict! +'H' C0-DF net/bluetooth/bnep/bnep.h conflict! +'I' all linux/isdn.h conflict! +'I' 00-0F drivers/isdn/divert/isdn_divert.h conflict! +'I' 40-4F linux/mISDNif.h conflict! 'J' 00-1F drivers/scsi/gdth_ioctl.h 'K' all linux/kd.h -'L' 00-1F linux/loop.h -'L' 20-2F driver/usb/misc/vstusb.h +'L' 00-1F linux/loop.h conflict! +'L' 10-1F drivers/scsi/mpt2sas/mpt2sas_ctl.h conflict! +'L' 20-2F linux/usb/vstusb.h 'L' E0-FF linux/ppdd.h encrypted disk device driver <http://linux01.gwdg.de/~alatham/ppdd.html> -'M' all linux/soundcard.h +'M' all linux/soundcard.h conflict! +'M' 01-16 mtd/mtd-abi.h conflict! + and drivers/mtd/mtdchar.c +'M' 01-03 drivers/scsi/megaraid/megaraid_sas.h +'M' 00-0F drivers/video/fsl-diu-fb.h conflict! 'N' 00-1F drivers/usb/scanner.h -'O' 00-02 include/mtd/ubi-user.h UBI -'P' all linux/soundcard.h +'O' 00-06 mtd/ubi-user.h UBI +'P' all linux/soundcard.h conflict! +'P' 60-6F sound/sscape_ioctl.h conflict! +'P' 00-0F drivers/usb/class/usblp.c conflict! 'Q' all linux/soundcard.h -'R' 00-1F linux/random.h +'R' 00-1F linux/random.h conflict! +'R' 01 linux/rfkill.h conflict! +'R' 01-0F media/rds.h conflict! +'R' C0-DF net/bluetooth/rfcomm.h 'S' all linux/cdrom.h conflict! 'S' 80-81 scsi/scsi_ioctl.h conflict! 'S' 82-FF scsi/scsi.h conflict! +'S' 00-7F sound/asequencer.h conflict! 'T' all linux/soundcard.h conflict! +'T' 00-AF sound/asound.h conflict! 'T' all arch/x86/include/asm/ioctls.h conflict! -'U' 00-EF linux/drivers/usb/usb.h -'V' all linux/vt.h +'T' C0-DF linux/if_tun.h conflict! +'U' all sound/asound.h conflict! +'U' 00-0F drivers/media/video/uvc/uvcvideo.h conflict! +'U' 00-CF linux/uinput.h conflict! +'U' 00-EF linux/usbdevice_fs.h +'U' C0-CF drivers/bluetooth/hci_uart.h +'V' all linux/vt.h conflict! +'V' all linux/videodev2.h conflict! +'V' C0 linux/ivtvfb.h conflict! +'V' C0 linux/ivtv.h conflict! +'V' C0 media/davinci/vpfe_capture.h conflict! +'V' C0 media/si4713.h conflict! +'V' C0-CF drivers/media/video/mxb.h conflict! 'W' 00-1F linux/watchdog.h conflict! 'W' 00-1F linux/wanrouter.h conflict! -'X' all linux/xfs_fs.h +'W' 00-3F sound/asound.h conflict! +'X' all fs/xfs/xfs_fs.h conflict! + and fs/xfs/linux-2.6/xfs_ioctl32.h + and include/linux/falloc.h + and linux/fs.h +'X' all fs/ocfs2/ocfs_fs.h conflict! +'X' 01 linux/pktcdvd.h conflict! 'Y' all linux/cyclades.h -'[' 00-07 linux/usb/usbtmc.h USB Test and Measurement Devices +'Z' 14-15 drivers/message/fusion/mptctl.h +'[' 00-07 linux/usb/tmc.h USB Test and Measurement Devices <mailto:gregkh@suse.de> -'a' all ATM on linux +'a' all linux/atm*.h, linux/sonet.h ATM on linux <http://lrcwww.epfl.ch/linux-atm/magic.html> -'b' 00-FF bit3 vme host bridge +'b' 00-FF conflict! bit3 vme host bridge <mailto:natalia@nikhefk.nikhef.nl> +'b' 00-0F media/bt819.h conflict! +'c' all linux/cm4000_cs.h conflict! 'c' 00-7F linux/comstats.h conflict! 'c' 00-7F linux/coda.h conflict! -'c' 80-9F arch/s390/include/asm/chsc.h -'c' A0-AF arch/x86/include/asm/msr.h +'c' 00-1F linux/chio.h conflict! +'c' 80-9F arch/s390/include/asm/chsc.h conflict! +'c' A0-AF arch/x86/include/asm/msr.h conflict! 'd' 00-FF linux/char/drm/drm/h conflict! +'d' 02-40 pcmcia/ds.h conflict! +'d' 10-3F drivers/media/video/dabusb.h conflict! +'d' C0-CF drivers/media/video/saa7191.h conflict! 'd' F0-FF linux/digi1.h 'e' all linux/digi1.h conflict! -'e' 00-1F net/irda/irtty.h conflict! -'f' 00-1F linux/ext2_fs.h -'h' 00-7F Charon filesystem +'e' 00-1F drivers/net/irda/irtty-sir.h conflict! +'f' 00-1F linux/ext2_fs.h conflict! +'f' 00-1F linux/ext3_fs.h conflict! +'f' 00-0F fs/jfs/jfs_dinode.h conflict! +'f' 00-0F fs/ext4/ext4.h conflict! +'f' 00-0F linux/fs.h conflict! +'f' 00-0F fs/ocfs2/ocfs2_fs.h conflict! +'g' 00-0F linux/usb/gadgetfs.h +'g' 20-2F linux/usb/g_printer.h +'h' 00-7F conflict! Charon filesystem <mailto:zapman@interlan.net> -'i' 00-3F linux/i2o.h +'h' 00-1F linux/hpet.h conflict! +'i' 00-3F linux/i2o-dev.h conflict! +'i' 0B-1F linux/ipmi.h conflict! +'i' 80-8F linux/i8k.h 'j' 00-3F linux/joystick.h +'k' 00-0F linux/spi/spidev.h conflict! +'k' 00-05 video/kyro.h conflict! 'l' 00-3F linux/tcfs_fs.h transparent cryptographic file system <http://mikonos.dia.unisa.it/tcfs> 'l' 40-7F linux/udf_fs_i.h in development: <http://sourceforge.net/projects/linux-udf/> -'m' 00-09 linux/mmtimer.h +'m' 00-09 linux/mmtimer.h conflict! 'm' all linux/mtio.h conflict! 'm' all linux/soundcard.h conflict! 'm' all linux/synclink.h conflict! +'m' 00-19 drivers/message/fusion/mptctl.h conflict! +'m' 00 drivers/scsi/megaraid/megaraid_ioctl.h conflict! 'm' 00-1F net/irda/irmod.h conflict! -'n' 00-7F linux/ncp_fs.h +'n' 00-7F linux/ncp_fs.h and fs/ncpfs/ioctl.c 'n' 80-8F linux/nilfs2_fs.h NILFS2 -'n' E0-FF video/matrox.h matroxfb +'n' E0-FF linux/matroxfb.h matroxfb 'o' 00-1F fs/ocfs2/ocfs2_fs.h OCFS2 -'o' 00-03 include/mtd/ubi-user.h conflict! (OCFS2 and UBI overlaps) -'o' 40-41 include/mtd/ubi-user.h UBI -'o' 01-A1 include/linux/dvb/*.h DVB +'o' 00-03 mtd/ubi-user.h conflict! (OCFS2 and UBI overlaps) +'o' 40-41 mtd/ubi-user.h UBI +'o' 01-A1 linux/dvb/*.h DVB 'p' 00-0F linux/phantom.h conflict! (OpenHaptics needs this) +'p' 00-1F linux/rtc.h conflict! 'p' 00-3F linux/mc146818rtc.h conflict! 'p' 40-7F linux/nvram.h -'p' 80-9F user-space parport +'p' 80-9F linux/ppdev.h user-space parport <mailto:tim@cyberelk.net> -'p' a1-a4 linux/pps.h LinuxPPS +'p' A1-A4 linux/pps.h LinuxPPS <mailto:giometti@linux.it> 'q' 00-1F linux/serio.h -'q' 80-FF Internet PhoneJACK, Internet LineJACK - <http://www.quicknet.net> -'r' 00-1F linux/msdos_fs.h +'q' 80-FF linux/telephony.h Internet PhoneJACK, Internet LineJACK + linux/ixjuser.h <http://www.quicknet.net> +'r' 00-1F linux/msdos_fs.h and fs/fat/dir.c 's' all linux/cdk.h 't' 00-7F linux/if_ppp.h 't' 80-8F linux/isdn_ppp.h +'t' 90 linux/toshiba.h 'u' 00-1F linux/smb_fs.h -'v' 00-1F linux/ext2_fs.h conflict! 'v' all linux/videodev.h conflict! +'v' 00-1F linux/ext2_fs.h conflict! +'v' 00-1F linux/fs.h conflict! +'v' 00-0F linux/sonypi.h conflict! +'v' C0-CF drivers/media/video/ov511.h conflict! +'v' C0-DF media/pwc-ioctl.h conflict! +'v' C0-FF linux/meye.h conflict! +'v' C0-CF drivers/media/video/zoran/zoran.h conflict! +'v' D0-DF drivers/media/video/cpia2/cpia2dev.h conflict! 'w' all CERN SCI driver 'y' 00-1F packet based user level communications <mailto:zapman@interlan.net> -'z' 00-3F CAN bus card +'z' 00-3F CAN bus card conflict! <mailto:hdstich@connectu.ulm.circular.de> -'z' 40-7F CAN bus card +'z' 40-7F CAN bus card conflict! <mailto:oe@port.de> +'z' 10-4F drivers/s390/crypto/zcrypt_api.h conflict! 0x80 00-1F linux/fb.h 0x81 00-1F linux/videotext.h +0x88 00-3F media/ovcamchip.h 0x89 00-06 arch/x86/include/asm/sockios.h 0x89 0B-DF linux/sockios.h 0x89 E0-EF linux/sockios.h SIOCPROTOPRIVATE range +0x89 E0-EF linux/dn.h PROTOPRIVATE range 0x89 F0-FF linux/sockios.h SIOCDEVPRIVATE range 0x8B all linux/wireless.h 0x8C 00-3F WiNRADiO driver <http://www.proximity.com.au/~brian/winradio/> 0x90 00 drivers/cdrom/sbpcd.h +0x92 00-0F drivers/usb/mon/mon_bin.c 0x93 60-7F linux/auto_fs.h +0x94 all fs/btrfs/ioctl.h 0x99 00-0F 537-Addinboard driver <mailto:buk@buks.ipn.de> 0xA0 all linux/sdp/sdp.h Industrial Device Project @@ -192,17 +302,22 @@ Code Seq# Include File Comments 0xAB 00-1F linux/nbd.h 0xAC 00-1F linux/raw.h 0xAD 00 Netfilter device in development: - <mailto:rusty@rustcorp.com.au> + <mailto:rusty@rustcorp.com.au> 0xAE all linux/kvm.h Kernel-based Virtual Machine <mailto:kvm@vger.kernel.org> 0xB0 all RATIO devices in development: <mailto:vgo@ratio.de> 0xB1 00-1F PPPoX <mailto:mostrows@styx.uwaterloo.ca> +0xC0 00-0F linux/usb/iowarrior.h 0xCB 00-1F CBM serial IEC bus in development: <mailto:michael.klein@puffin.lb.shuttle.de> +0xCD 01 linux/reiserfs_fs.h +0xCF 02 fs/cifs/ioctl.c +0xDB 00-0F drivers/char/mwave/mwavepub.h 0xDD 00-3F ZFCP device driver see drivers/s390/scsi/ <mailto:aherrman@de.ibm.com> -0xF3 00-3F video/sisfb.h sisfb (in development) +0xF3 00-3F drivers/usb/misc/sisusbvga/sisusb.h sisfb (in development) <mailto:thomas@winischhofer.net> 0xF4 00-1F video/mbxfb.h mbxfb <mailto:raph@8d.com> +0xFD all linux/dm-ioctl.h diff --git a/Documentation/kernel-doc-nano-HOWTO.txt b/Documentation/kernel-doc-nano-HOWTO.txt index 348b9e5e28fc..27a52b35d55b 100644 --- a/Documentation/kernel-doc-nano-HOWTO.txt +++ b/Documentation/kernel-doc-nano-HOWTO.txt @@ -214,11 +214,13 @@ The format of the block comment is like this: * (section header: (section description)? )* (*)?*/ -The short function description ***cannot be multiline***, but the other -descriptions can be (and they can contain blank lines). If you continue -that initial short description onto a second line, that second line will -appear further down at the beginning of the description section, which is -almost certainly not what you had in mind. +All "description" text can span multiple lines, although the +function_name & its short description are traditionally on a single line. +Description text may also contain blank lines (i.e., lines that contain +only a "*"). + +"section header:" names must be unique per function (or struct, +union, typedef, enum). Avoid putting a spurious blank line after the function name, or else the description will be repeated! diff --git a/Documentation/trace/ring-buffer-design.txt b/Documentation/trace/ring-buffer-design.txt index 5b1d23d604c5..d299ff31df57 100644 --- a/Documentation/trace/ring-buffer-design.txt +++ b/Documentation/trace/ring-buffer-design.txt @@ -33,9 +33,9 @@ head_page - a pointer to the page that the reader will use next tail_page - a pointer to the page that will be written to next -commit_page - a pointer to the page with the last finished non nested write. +commit_page - a pointer to the page with the last finished non-nested write. -cmpxchg - hardware assisted atomic transaction that performs the following: +cmpxchg - hardware-assisted atomic transaction that performs the following: A = B iff previous A == C @@ -52,15 +52,15 @@ The Generic Ring Buffer The ring buffer can be used in either an overwrite mode or in producer/consumer mode. -Producer/consumer mode is where the producer were to fill up the +Producer/consumer mode is where if the producer were to fill up the buffer before the consumer could free up anything, the producer will stop writing to the buffer. This will lose most recent events. -Overwrite mode is where the produce were to fill up the buffer +Overwrite mode is where if the producer were to fill up the buffer before the consumer could free up anything, the producer will overwrite the older data. This will lose the oldest events. -No two writers can write at the same time (on the same per cpu buffer), +No two writers can write at the same time (on the same per-cpu buffer), but a writer may interrupt another writer, but it must finish writing before the previous writer may continue. This is very important to the algorithm. The writers act like a "stack". The way interrupts works @@ -79,16 +79,16 @@ the interrupt doing a write as well. Readers can happen at any time. But no two readers may run at the same time, nor can a reader preempt/interrupt another reader. A reader -can not preempt/interrupt a writer, but it may read/consume from the +cannot preempt/interrupt a writer, but it may read/consume from the buffer at the same time as a writer is writing, but the reader must be on another processor to do so. A reader may read on its own processor and can be preempted by a writer. -A writer can preempt a reader, but a reader can not preempt a writer. +A writer can preempt a reader, but a reader cannot preempt a writer. But a reader can read the buffer at the same time (on another processor) as a writer. -The ring buffer is made up of a list of pages held together by a link list. +The ring buffer is made up of a list of pages held together by a linked list. At initialization a reader page is allocated for the reader that is not part of the ring buffer. @@ -102,7 +102,7 @@ the head page. The reader has its own page to use. At start up time, this page is allocated but is not attached to the list. When the reader wants -to read from the buffer, if its page is empty (like it is on start up) +to read from the buffer, if its page is empty (like it is on start-up), it will swap its page with the head_page. The old reader page will become part of the ring buffer and the head_page will be removed. The page after the inserted page (old reader_page) will become the @@ -206,7 +206,7 @@ The main pointers: commit page - the page that last finished a write. -The commit page only is updated by the outer most writer in the +The commit page only is updated by the outermost writer in the writer stack. A writer that preempts another writer will not move the commit page. @@ -281,7 +281,7 @@ with the previous write. The commit pointer points to the last write location that was committed without preempting another write. When a write that preempted another write is committed, it only becomes a pending commit -and will not be a full commit till all writes have been committed. +and will not be a full commit until all writes have been committed. The commit page points to the page that has the last full commit. The tail page points to the page with the last write (before @@ -292,7 +292,7 @@ be several pages ahead. If the tail page catches up to the commit page then no more writes may take place (regardless of the mode of the ring buffer: overwrite and produce/consumer). -The order of pages are: +The order of pages is: head page commit page @@ -311,7 +311,7 @@ Possible scenario: There is a special case that the head page is after either the commit page and possibly the tail page. That is when the commit (and tail) page has been swapped with the reader page. This is because the head page is always -part of the ring buffer, but the reader page is not. When ever there +part of the ring buffer, but the reader page is not. Whenever there has been less than a full page that has been committed inside the ring buffer, and a reader swaps out a page, it will be swapping out the commit page. @@ -338,7 +338,7 @@ and a reader swaps out a page, it will be swapping out the commit page. In this case, the head page will not move when the tail and commit move back into the ring buffer. -The reader can not swap a page into the ring buffer if the commit page +The reader cannot swap a page into the ring buffer if the commit page is still on that page. If the read meets the last commit (real commit not pending or reserved), then there is nothing more to read. The buffer is considered empty until another full commit finishes. @@ -395,7 +395,7 @@ The main idea behind the lockless algorithm is to combine the moving of the head_page pointer with the swapping of pages with the reader. State flags are placed inside the pointer to the page. To do this, each page must be aligned in memory by 4 bytes. This will allow the 2 -least significant bits of the address to be used as flags. Since +least significant bits of the address to be used as flags, since they will always be zero for the address. To get the address, simply mask out the flags. @@ -460,7 +460,7 @@ When the reader tries to swap the page with the ring buffer, it will also use cmpxchg. If the flag bit in the pointer to the head page does not have the HEADER flag set, the compare will fail and the reader will need to look for the new head page and try again. -Note, the flag UPDATE and HEADER are never set at the same time. +Note, the flags UPDATE and HEADER are never set at the same time. The reader swaps the reader page as follows: @@ -539,7 +539,7 @@ updated to the reader page. | +-----------------------------+ | +------------------------------------+ -Another important point. The page that the reader page points back to +Another important point: The page that the reader page points back to by its previous pointer (the one that now points to the new head page) never points back to the reader page. That is because the reader page is not part of the ring buffer. Traversing the ring buffer via the next pointers @@ -572,7 +572,7 @@ not be able to swap the head page from the buffer, nor will it be able to move the head page, until the writer is finished with the move. This eliminates any races that the reader can have on the writer. The reader -must spin, and this is why the reader can not preempt the writer. +must spin, and this is why the reader cannot preempt the writer. tail page | @@ -659,9 +659,9 @@ before pushing the head page. If it is, then it can be assumed that the tail page wrapped the buffer, and we must drop new writes. This is not a race condition, because the commit page can only be moved -by the outter most writer (the writer that was preempted). +by the outermost writer (the writer that was preempted). This means that the commit will not move while a writer is moving the -tail page. The reader can not swap the reader page if it is also being +tail page. The reader cannot swap the reader page if it is also being used as the commit page. The reader can simply check that the commit is off the reader page. Once the commit page leaves the reader page it will never go back on it unless a reader does another swap with the @@ -733,7 +733,7 @@ The write converts the head page pointer to UPDATE. --->| |<---| |<---| |<---| |<--- +---+ +---+ +---+ +---+ -But if a nested writer preempts here. It will see that the next +But if a nested writer preempts here, it will see that the next page is a head page, but it is also nested. It will detect that it is nested and will save that information. The detection is the fact that it sees the UPDATE flag instead of a HEADER or NORMAL @@ -761,7 +761,7 @@ to NORMAL. --->| |<---| |<---| |<---| |<--- +---+ +---+ +---+ +---+ -After the nested writer finishes, the outer most writer will convert +After the nested writer finishes, the outermost writer will convert the UPDATE pointer to NORMAL. @@ -812,7 +812,7 @@ head page. +---+ +---+ +---+ +---+ The nested writer moves the tail page forward. But does not set the old -update page to NORMAL because it is not the outer most writer. +update page to NORMAL because it is not the outermost writer. tail page | @@ -892,7 +892,7 @@ It will return to the first writer. --->| |<---| |<---| |<---| |<--- +---+ +---+ +---+ +---+ -The first writer can not know atomically test if the tail page moved +The first writer cannot know atomically if the tail page moved while it updates the HEAD page. It will then update the head page to what it thinks is the new head page. @@ -923,9 +923,9 @@ if the tail page is either where it use to be or on the next page: --->| |<---| |<---| |<---| |<--- +---+ +---+ +---+ +---+ -If tail page != A and tail page does not equal B, then it must reset the -pointer back to NORMAL. The fact that it only needs to worry about -nested writers, it only needs to check this after setting the HEAD page. +If tail page != A and tail page != B, then it must reset the pointer +back to NORMAL. The fact that it only needs to worry about nested +writers means that it only needs to check this after setting the HEAD page. (first writer) @@ -939,7 +939,7 @@ nested writers, it only needs to check this after setting the HEAD page. +---+ +---+ +---+ +---+ Now the writer can update the head page. This is also why the head page must -remain in UPDATE and only reset by the outer most writer. This prevents +remain in UPDATE and only reset by the outermost writer. This prevents the reader from seeing the incorrect head page. |