Carry Flag

OS X IP alias

2011-01-29T19:43:00.002+02:00

To avoid reconfiguring interfaces for repeated router setups, decided to find out how to add an IP alias in Mac OS X:sudo ifconfig en1 alias 192.168.1.195 netmask 255.255.255.0aplawrence.com

gdb tricks

2011-01-26T17:17:00.002+02:00

Excellent gdb examples at ksplice.com blog.gdb --argsdirectoryset substitute path-ggdb3 to gdb optimized debug symbols; macro expand

Linux SPI

2010-09-18T10:00:00.000+03:00

My notes while reading about Linux and SPI.De facto - no standardization like i2c/smbus.Master/slave like i2cFaster clock 10MHz vs 400kHz i2cFull duplex, unlike i2c.Daisy chaining (in addition to / instead of) wired-AND bus like i2c.Dedicated chip select signals instead of i2c addressing.Linux software support only applies to master side, like i2c.Four clocking modes (?)- CPOL - clock starts low(

Filter selection through pipe in Emacs

2010-08-20T07:48:00.000+03:00

Emacs has this wonderful feature of filtering a selection through a unix pipe. It's just a bit hard to remember how to invoke.C-u M-| command RET

RPM cheat sheet

2010-08-19T07:12:00.000+03:00

list installed packages, dpkg -l rpm -qainfo on an installed package, dpkg -s rpm -qicontents of an installed package, dpkg -L rpm -q -lpackage where a file belongs to, dpkg -S rpm -q -fextract package contents without installing, dpkg -x rpm2cpio file.rpm | cpio -idv

debugging makefile variables

2010-08-08T22:38:00.002+03:00

To debug makefile variable assigments. Use make -p (--print-data-base) to see which values get assigned to variables and where.Need to add to reading list: Managing projects with GNU make.

OpenSSH host key signature fingerprint

2010-08-04T07:25:00.000+03:00

Note to self. It's ssh-keygen that can dump the host key fingerprint in a format suitable for PuTTY security alert comparisons. ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key.pub

Linux i2c

2010-06-24T15:26:00.005+03:00

My notes while reading Linux kernel i2c source code and the documentation.i2c-devimplements the character devices for userspace, a generic, "remote controlled" i2c chip driverioctl to select slaveread()/write() for a subset of smbus operationsi2c-tools with library functionsi2c adapterA host bus adapter instanceclass - allow probing for slave devices in class: HWMON, TV, DDC, SPDnr - 'id'

LDD3 notes: Networking

2010-06-17T11:26:00.000+03:00

Free UML tools

2010-06-12T20:56:00.001+03:00

Excellent summary of freely available UML tools, with screenshots.http://www.devcurry.com/2010/06/free-open-source-uml-tools.html

LDD3 notes: TTY

2010-06-10T07:34:00.003+03:00

My notes while reading Linux Device Drivers 3rd edition, TTY drivers.TTY drivers are a generic implementation of a serial port interface with loose coupling of hardware access and data formatting.It is a char device composed oftty core for user space char device interfaceline discipline for data formattingtty driver for hardware accesswrite can be called from interrupt context.must succeed for

iMovie event library on a network drive, NAS

2010-06-08T19:04:00.000+03:00

I was shocked to find that iMovie '09 would not allow storing event libraries on networked disks. The AFP volume would show up, but remain non-functional with a yellow exclamation sign.There are plenty of instructions for hacking around the limitation with clumsy symbolic links. I discovered a much simpler approach, using an undocumented (?) setting built right into iMovie:"Allow Network Volumes"

Mac Time Machine with Linux server

2010-06-08T07:50:00.000+03:00

Finally, an easy way to have Time Machine accept a Linux server as a backup disk.Upgrade to Ubuntu 10.4.Install netatalkAdd option "tm" to a share in AppleVolumes.default config file.No need to mess withManually created sparsebundlesShoehorn settings like TMShowUnsupportedNetworkVolumes The key is to have netatalk version 2.0.5 or above.

LDD3 notes: DMA

2010-06-03T07:02:00.000+03:00

My notes while reading Linux Device Drivers 3rd edition, Memory mapping and DMA.Kernel addressingPhysical address Logical AddressVirtual addressBus address (physical address as understood by the DMA peripheral) __pa() , __va() for low memory onlyConceptsPFN - page frame number. (virtual or physical) address / page sizestruct page'handle' to a page of memory. page_address() macro to get virtual

LDD3 notes: Driver Model

2010-05-27T07:10:00.003+03:00

My notes while reading Linux Device Drivers 3rd edition.2.6 device model addresses aspects common to all types of devices:Power managementUserspace communications /sysfsHotplugging w/ udevDevice classesObject lifecycleKobject, Kset, Subsystemkobject per object, belongs to a ktype.kset for a collection of kobjects of same typeSubsystem as a high-level portion of the kernel as a whole: block,

LDD3 notes: USB

2010-05-20T22:13:00.000+03:00

My notes while reading Linux Device Drivers 3rd edition.Generalnaming: root_hub-hub_port[-hub_port]:config.interfacewrite to bConfigurationValue will switch configuration & bound driver URBs skbuff analogyqueued, async, acknowledgedusb_alloc_urb(), usb_fill_[int|bulk]_urb(), usb_submit_urb()transfer buffers must be kmalloc():ed, not static or automatic device_id's can match specific vendor/

vmware player network configuration

2010-05-19T07:40:00.000+03:00

Vmware player 3.0.1 is a surprisingly capable and free virtualization environment. "Player" in the name is a bit misleading as many of the restrictions in earlier versions have been lifted.However, network configuration tool is not installed by default and needs to be manually extracted.Richard at f5 devcentral provides the details:You can install it manually by extracting it from the install

LDD3 notes: Data types

2010-05-13T22:11:00.000+03:00

My notes while reading Linux Device Drivers 3rd edition. size_t vs ssize_t for negative values as error codes C99 [u]intptr_t, integer which would fit a pointer. Not used in Linux. Similar to eCos cyg_addrword. fixed size integers u8..s32 within kernelioctl structures shared with userspace use prefix __u8 _t Typedefs for portability onlyout of fashioninconvenient printk use Important constants:

LDD3 notes: Memory

2010-05-06T22:07:00.000+03:00

My notes while reading Linux Device Drivers 3rd edition.Allocation Flags - GFP_KERNEL - system call, i.e. behalf of a process running in kernel -> may sleep - GFP_ATOMIC - won't sleep, but has limited memory available Slab caches for quick allocation of constant size objects ( == object pool ) - a.k.a lookaside cache - ctor/dtor can be called in atomic context, indicated by a flag Mempool - a

Insert a picture by reference in MS Word

2010-05-04T12:39:00.003+03:00

I've always disliked manual, repetitive tasks with MS Word. There is one less to worry about, now that I've found about inserting and linking pictures.In insert picture file dialog, select "Insert and Link", tomake a link referencing the original file to keep it automatically updated when the picture changes.have an embedded copy in the document to avoid broken links when sending out the Word

LDD3 notes: Passage of time

2010-04-29T22:04:00.000+03:00

My notes while reading Linux Device Drivers 3rd edition.Jiffies get_jiffies_64()comparison macros: time_after/beforejiffies <-> timeval / timespecget_cycles()short busy waits n/u/mdelay() 1ms/1s resolution sleeps msleep(), ssleep() Working with 1/HZ resolution sleeps wait_event_timeout() - returns timeout left, never negativeset_current_state(interruptible), schedule_timeout()in_atomic(),

RCU

2010-04-26T11:11:00.000+03:00

Reading a few LWN articles on RCUs (1 2 3) really shed some light on their properties and use.On read-intensive scenarios, it's more efficient to replace read/write locking with an RCU. This is possible because all Linux platforms have atomic pointer read/write operations.Read critical sectiondereferences pointers through a mechanism with platform specific memory ordering guarantees:

LDD3 notes: Concurrency

2010-04-22T22:01:00.000+03:00

My notes while reading Linux Device Drivers 3rd edition.Reasons to pay attention to concurrencyEarly kernels had no SMP, no pre-emption -> enough to protect from interruptsSMP and pre-emption both pose similar concurrency requirements, even though you'd be willing to ignore the other one.shared resources -> avoid semaphores: sema_init, up, down (declare_mutex) read/write semaphore pairs:

LDD3 notes: Debugging

2010-04-15T21:56:00.000+03:00

My notes while reading Linux Device Drivers 3rd edition.printk_ratelimit() tells if we're not flooding the logKernel configuration CONFIG_DEBUG_SLAB -> canary killedCONFIG_DEBUG_SPINLOCK_SLEEP -> potential sleeps with spinlocks detectedCONFIG_DEBUG_INFO, CONFIG_FRAME_POINTER for gdb debugging seq_file - kernel in-memory file buffer, similar to open_memstream or ostringstream. a cleaner interface

LDD3 notes: Device registration and operations

2010-04-08T21:53:00.000+03:00

My notes while reading Linux Device Drivers 3rd edition. register_chrdrv replaced with cdev_add(), cdev_del() and struct cdev register_chrdev_region, alloc_chrdev_region, unregister_chrdev_region to statically, dynamically pick a contiguous block of dev_t's i.e. major and minor numbers.assign them a device name ( /dev/devices and sysfs )no need to know major/minor numbers at open look at inode->

LDD3 notes: Compiling and loading modules

2010-04-01T21:45:00.003+03:00

My notes while reading Linux Device Drivers 3rd edition. out of tree module makefile boilerplate with dual purpose standalone: invokes kernel tree modules targetreferenced by M: acts like in-tree kbuild makefile disposable sections with __init, __initdata, __exit module loading races register facilities only when really ready to take callsat failure, previously registered facilities can be in

Shared libraries and ELF

2010-03-25T15:47:00.000+02:00

I just finished reading How to write Shared Libraries by Ulrich Drepper, a very nice guide to understanding the details of dynamic linking and use of ELF format with Linux.ELF structure like program header and segmentsClear explanation of GOT and PLT with concrete examplesTypes of relocations: relative, symbol relocation and evils of TEXTRELTracing dynamic linking w/ LD_DEBUGconcept of gnu-hash

gnu binutils

2010-03-24T07:48:00.003+02:00

I decided to read through the man pages of binutils, to see if there's something interesting I've never come across. The only things that were not previously very familiar were the c++filt and addr2line tools. Anyway, here are the notes I made while reading about each of the tools in the binutils package.ar and ranlibmanage archives: static libraries of compiled object files. Most often these

Dangers of C library

2010-03-22T14:22:00.004+02:00

I just read through Ulrich Drepper's Defensive Programming article. He highlights dangers of C library, provides safer alternatives for commonly used idioms and introduces a number of tools for pinpointing problems in code.These are my rather unstructured notes of things most interesting to me.Syntax for forward declarations within paramer list and array size annotation for future checks int

Booting Linux over JTAG

2010-03-18T16:36:00.001+02:00

Note to self. A working gdb script to boot Linux kernel on an atmel board over JTAG.Unfortunately this is not completely automatic. u-boot needs to be interrupted for loading the uImage through gdb. U-boot can then be resumed and kernel booted with bootm 0x22000000.Also, either the emulator needs to be configured to ignore data aborts or kernel futex support to be disabled.target remote emulator

Optimizing with gcc

2010-03-14T12:13:00.003+02:00

My notes while reading Optimizing applications with gcc & glibc by Ulrich Drepper.__extension__ to mark intentional use of GNU extension.poor mans 'lambda' (({ })) predicate to determine if parameter value is constant at runtime: __builtin_constant_p()mark pure functions with __attribute__((__const__))mark functions which never return with __attribute__((__noreturn__))__stdcall__ attribute on x86

Eclipse CDT

2010-03-13T12:59:00.004+02:00

I'll have to try out the Eclipse CDT sometime- integration of native development tools such as the GNU Autotools: Linux Tools- a plugin to explore remote system files through Eclipse: eclipse-rse

64bit PC's and memory

2010-03-10T10:45:00.001+02:00

Just to refresh my knowledge on the PC platforms, I read the excellent Wikipedia article on the 64-bit x86.PC processors and 64-bitnessThe current 64-bit instruction set is a backwards compatible extension to the Intel instruction set. It is implemented in all typical processors from all common vendors. It has multiple confusing names, all meaning the same: Intel 64, amd64, EM64T, x86_64, x86-64,

Linux Kernel in a nutshell

2010-03-08T07:00:00.001+02:00

Although I've been working with Linux kernel for ages, I decided to browse through Linux Kernel in a nutshell, an excellent book on the practical things regarding working with the kernel. There certainly were things that I was not aware of. Here are my notes on these things.Using a read-only source tree with O=/path/to/build/output Some basic static analysis with sparse with C=1 or C=2.

USB logic analyzer from Saleae

2010-01-23T03:46:00.001+02:00

Yesterday I received my Logic, an affordable USB-attached logic analyzer.The software for Mac OS X is in early stages with very basic capture functionality only. But it already helped me troubleshoot one system.I've used its Windows software in the past, which is much better. I hope the features like integrated protocol analyzers will be soon be part of the Mac package as well.

Safari beachballing solved

2009-12-31T21:36:00.002+02:00

Safari 4 on Snow Leopard seemed to be getting slower each day. Especially opening the top sites view could hang with a beach ball for a minute.Fortunately all this was solved simply by changing the default RSS reader from Safari to Mail.

IGEP or beagleboard

2009-12-15T07:00:00.000+02:00

Beagleboard would be an interesting toy. If it only had Ethernet. IGEPv2 seems like a good alternative. Roughly the same specs and price, with Ethernet included.

beautiful ascii graphics

2009-11-23T07:43:00.002+02:00

Text is graphics is text:JavE - a graphics editor for editing textsditaa - DIagrams Through Ascii Art ASCIIO - draw ASCII charts using a GUI

Progress bar on any unix pipe

2009-11-05T07:32:00.002+02:00

pv adds progress bar to any unix pipe. There's a nice tutorial on it by Peter Krumins.

Windows App Store / apt-get for Windows

2009-10-26T07:45:00.000+02:00

I don't see myself switching back to Windows, but these could turn out useful at work or with family.Windows software installation is no fun after getting used to Debian Linux or macports. These tools together could be a poor mans apt-get for Windows:PcDecrapifier - To unload the unwanted preloaded software.Ninite - To easily load all the common software.BaseShield - An alternative to Ninite,

public samba share

2009-10-20T07:11:00.000+03:00

I've often found it difficult to set up a public shared directory using Samba, so that windows workstations could access it easily without passwords or anything.This time I tried these excellent instructions and it worked right away on a debian lenny/sid box and Windows XP.Configuring anonymous public shares with Samba 3

Subversion repository fix

2009-10-15T07:31:00.002+03:00

A locally accessed subversion repository is a bit fragile on unix permissions.It might work fine for first 1000 revisions, and then suddenly all svn operations fail with an error: svn: Can't move '/home/svn/...' to '/home/svn/...': Permission deniedFortunately this is easy to fix by making sure the- shared directories have group 'svn'- shared directories have mode 2775- and that the svn is

easy debian server monitoring

2009-10-01T07:07:00.002+03:00

Finally I ran into a tool to quickly set up monitoring of a Debian server."aptitude install munin"It graphs more than I was hoping for, including: disk space, cpu load, network and even disk smart parameters.Basic configuration of alerts is simple, edit /etc/munin/munin.conf- Uncomment and edit a contact -line- Determine name of plugin to configure, for example "cpu" - it's the suffix after

iTunes and car audio synchronization.

2009-09-30T07:11:00.001+03:00

My car has a USB socket for MP3/AAC audio, but so far it has been to much of a trouble to regularly fill up a flash drive with music and podcasts. iTuneMyWalkman is originally made for synchronizing a mobile phone, but it seems to work great with any flash drive.Only thing better would be an iPod dock on the dashboard.

From Parallels to VirtualBox

2009-09-29T07:33:00.000+03:00

I had Parallels 3.0 for running Linux virtual machines on my Mac. Upgrade to Snow Leopard would have required the purchase of upgrade to Parallels 4.0.Instead, I tried uninstalling Parallels and setting up Sun VirtualBox 3.0.6. This works fine with Snow Leopard and the whole system with the virtual machines running feel much more responsive.Unfortunately I had to discard the old virtual machines

Diagrams without drawing

2009-09-28T07:08:00.000+03:00

I've always preferred keyboard over mouse, so I've found these tools very interestingsdedit: quick sequence diagram editor.umlgraph a tool for declarative specification and drawing of UML class and sequence diagrams.

Robust bash scripts

2009-09-27T07:36:00.000+03:00

A practical guide to making your bash scrips a bit more robust.

Reading on git

2009-09-26T07:34:00.001+03:00

Pro Git, an online book on git.Git Magic.

2009-09-25T07:33:00.000+03:00

Qucs a Quite Universal Circuit Simulator, is a circuit simulator with graphical user interface.

Open Test Lab

2009-09-24T10:18:00.000+03:00

CE Linux Forum Open Test Lab seems like a nice effort for automated testing of Linux on various embedded platforms.

Software Carpentry

2009-09-23T10:30:00.000+03:00

An open source intensive introduction course to basic software development practices for scientists and engineers