painful debugging due to forget to cancel asynchronous IO operations

Under windows, you can issue asynchronous IO operations to the kernel. sometimes, you are impatient  to wait for the completion of the operation. Then you need to use CancelIoEx() to cancel this operation.

My recent code does not cancel the operation and I simply free the hEvent associated with the asynchronous IO operation. The consequence is extremely severe. The stack of my program has been tampered. I experienced STATUS_STACK_BUFFER_OVERRUN error.

It was a futile effort and I spent lots of time understand the STATUS_STACK_BUFFER_OVERRUN error and lots of time examine the assembly code. Then I found out the code stack has been modified by someone else. Then I began to re-check the entire code logic and finally caught the culprit.

re-enable classic start menu on windows server 8

I am not a big fan for the metro-style UI on windows 8, especially on windows server 8. Therefore the very first thing after I installed a windows 8 server. I try to turn off the metro-style UI and get the classic start menu back. Here is how:

In regedit,

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer

change value of RPEnabled from "1" to "0"

Calling conventions of VC

VC has three calling conventions

• /Gd, the default setting, specifies the __cdecl calling convention for all functions except C++ member functions and functions marked __stdcall or __fastcall.
• /Gr specifies the __fastcall calling convention for all functions except C++ member sfunctions and functions marked __cdecl or __stdcall. All __fastcall functions must have prototypes.
• /Gz specifies the __stdcall calling convention for all functions except C++ member functions and functions marked __cdecl or __fastcall. All __stdcall functions must have prototypes.

Decorated Names for different calling conventions:

• For C, the __cdecl naming convention uses the function name preceded by an underscore ( _ ).  Generally the function arguments are passed on the stack in reverse order so that the callee can access them in the correct order. The caller is responsible for popping the arguments after the function returns, which makes it possible to use the ... to send runtime defined arguments. Return values are returned in the registers.
   _functionname
• For C, the __fastcall naming convention uses the function name preceded by an at sign (@) followed by the size of the function's arguments in bytes. Some of a __fastcall function's arguments are passed in registers (for x86 processors, ECX and EDX), and the rest are pushed onto the stack from right to left. The called routine pops these arguments from the stack before it returns. @function_name@number
• For C, the __stdcall naming convention uses the function name preceded by an underscore ( _ ) and followed by an at sign (@) and the size of the function's arguments in bytes. A __stdcall function's arguments are pushed onto the stack from right to left, and the called function pops these arguments from the stack before it returns. _functionname@number

Calling Conventions supported by VC

EINTR

long time ago, I knew that certain system call will returned EINTR during block. But I did not know why, so forget to ask why. Until recently, I start to think about this problem, the answer turns out to be in a long time ago favorable book APUE.

"A characteristic of earlier UNIX systems is that if a process caught a signal while the process was blocked in a "slow" system call, the system call was interrupted. The system call returned an error and errno was set to EINTR. This was done under the assumption that since a signal occurred and the process caught it, there is a good chance that something has happened that should wake up the blocked system call.
" --Section 10.5. Richard Stevens.

openflow indigo artchitecture

Indigo is project to produce OpenFlow enabled hardware switch. Here is the software architecture of OpenFlow enabled hardware switch they posted on their website.

Here we can see several long running processes. But there is no details about the functionality of each process. Which serves for the openflow controller? Here is the missing information. As you can see, the ofprotocol and ofdatapath actually talk to the openflow controllers and monitors.

identify the cause of high cpu utilization via xperf

1. Install xperf. Now xperf is in windows SDK. The setup file is wpt_x64.exe for amd64.

2. Start tracing
xperf -on latency -stackwalk Profile

3. After a while, stop tracing and generate trace file trace.etl.
xperf -d trace.etl

4. analyze the result. You need to provide pdb file to show the function name.
xperf trace.etl

As you can see sal_usleep() is the culprit and takes most of CPU time.

After we fix sal_usleep(), the CPU utilization drops significantly.

Another powerful feature of xperf is stack walking. It will output call stacks of a function. More information can be find here (stack walking) and here (enable stack walking on x64).

sending packets from multi-home host

The Next Generation TCP/IP stack in Windows Vista and Windows Server 2008 supports strong host sends and receives for both IPv4 and IPv6 by default on all interfaces except the Teredo tunneling interface for a Teredo host-specific relay. 

Strong and Weak Host Models

You are unable to view Roles and Features and receive error code 0x800706BE in Server Manager

check this article.

1. Microsoft Update Readiness Tool. http://support.microsoft.com/kb/947821
2. Check C:\Windows\logs\CBS\Checksur.log
3. takeown /F c:\Windows\Servicing\Packages /D y /R
4. cacls c:\Windows\Servicing\Packages /E /T /C /G "UserName":F
5. Download the KB Files for the missing files:
6. Expand -F:* UpdateKBXXXX.msu x:\DestinationDirectory
7. Expand -F:* UpdateKBXXXX.CAB x:\DestinationDirectoryCAB
8. Copy missing or corrupted files.

HTPC

AMD’s APU Fusion solution

• Single or Dual-core 64-bit processors codenamed Ontario, Zacate and with the followings:
  • made on 40 nm CMOS process
  • support for DDR3 1066 MHz memory
  • 9W or 18W TDP
• Radeon HD 6xxx GPU on 40 nm process
  • Cedar graphics core with 80 SP
  • DirectX 11, OpenGL 4.0 and OpenCL 1.1
  • UNB/MC Bus interface
  • no double-precision FP
  • angle independent anisotropic filtering, UVD 3
  • Eyefinity capabilities, supporting up to 3 outputs

Mobile chipset: A50M (Hudson-M1) 4.7W TDP

Hudson Chipset comparision

Overall, AMD E-350 series platforms is suitable for HTPC. It can do hardware HD decoding. Overall power is around 40W. There are plenty motherboard built around E-350 platforms. We’ll introduce them in next blog.

linux time in hyper-v

windows Bios does not support UTC hardware time. Therefore, the Bios hardware time for a windows server is always set to local time. However, linux treats that time as UTC by default. Thus for a linux virtual machine running in hyper-v it will treat the localtime as UTC cause incorrect time.

Here is what you should do:

set in /etc/default/rcS UTC=no

Then use tzselect to select correct time zone.

ioctl method

the difference among METHOD_BUFFERED, METHOD_IN_DIRECT and METHOD_OUT_DIRECT.

osronline has an article about this, check here.

codeproject has an example about this, check here.

Switch system volumn in windows 2008 R2

First, here is the definition for system volume and boot volume under windows.

Second, here is step to change system volume from HDD3 to HDD1.

1. The boot files consist of a folder called "Boot" and an application called "bootmgr". They are system files, and so are normally hidden. You must make them visible.
2. Copy them both from HDD3 to HDD1. It will complain that two files cannot be copied: "BCD" and "BCD.log", both of which are in the "Boot" folder. The latter is unimportant (its just a log file) and can be ignored; the former will be copied in the next step.
3. Open a command prompt with Administrator privileges. Type the following command "bcdedit /export HDD1:\Boot\BCD", where HDD1 is the driver letter of your destination drive. In my case, HDD1 was C, so the command was "bcdedit /export C:\Boot\BCD".
4. Now, you have to edit the BCD file so that the entries are all correct. I used the bcdedit program which comes with Windows 7, but there are others. I've heard EasyBCD is pretty good (and free), but the latest version doesn't fully support Windows 7. I believe a new version that does support Windows 7 will be out shortly. First, I navigate to HDD1\Boot on the command prompt (with Admin privileges) and type "bcdedit /store BCD /enum ALL". I use the /store switch to specify the BCD file in the current directory - omitting this switch will use the default one I think, which is on HDD3. This command lists all the entries in the BCD file.
5. I scanned the entries, and it turns out that the entries for {bootmgr} and {memdiag} both point to HDD3. Of course, I want them to point to HDD1. So I issue commands in the following form: "bcdedit /store BCD /set [entry name] device partition=HDD1:". Since HDD1 is C on my machine, I would type the following to set the {bootmgr} entry: "bcdedit /store BCD /set {bootmgr} device partition=C:".

That's about it. One last step is to make HDD1 Active via Disk Management (accessed from Computer Management) - it was already Active on my system, so I didn't have to do anything.