Installing py3exiv2 on MacOSX

pip install py3exiv2 –download=”/Users/jpadhye/python-exif/”

tar -zxf py3exiv2-0.2.1.tar.gz


cp py3exiv2-0.2.1/

tar -czf py3exiv2-0.2.1.tar.gz py3exiv2-0.2.1

brew install boost-python3

brew install gexiv2 pygobject pygobject3

pip install py3exiv2-0.2.1.tar.gz


Setting up VNC server on Raspberry Pi to autostart on reboot

First note down the IP address of your Pi

hostname -I

Make sure your packages are updated to latest version

sudo apt-get update
sudo apt-get install tightvncserver

Create a vnc server service description file

sudo vi /etc/init.d/tightvncserver

and the following code:

# Provides: tightvncserver
# Required-Start: $syslog
# Required-Stop: $syslog
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: vnc server
# Description:
# /etc/init.d/tightvncserver
# Set the VNCUSER variable to the name of the user to start tightvncserver under
case "$1" in
#Change the display number below. The connection port will be 5900 + display #
su $VNCUSER -c '/usr/bin/tightvncserver :1'
echo "Starting TightVNC server for $VNCUSER"
pkill Xtightvnc
echo "Tightvncserver stopped"
echo "Usage: /etc/init.d/tightvncserver {start|stop}"
exit 1
exit 0

If lines 2-11 are not added above you get the following error:

$ sudo update-rc.d tightvncserver defaults
insserv: warning: script 'tightvncserver' missing LSB tags and overrides

Modify the permissions on the file:

sudo chmod 755 /etc/init.d/tightvncserver
sudo update-rc.d tightvncserver defaults

Setup a password for vnc:

$ vncpasswd
Using password file /home/pi/.vnc/passwd
Would you like to enter a view-only password (y/n)? n

Test that your server works without any errors:

pi@myrpi:~ $ sudo /etc/init.d/tightvncserver start

New 'X' desktop is myrpi:1

Creating default startup script /home/pi/.vnc/xstartup
Starting applications specified in /home/pi/.vnc/xstartup
Log file is /home/pi/.vnc/myrpi:1.log

Now reboot your system and check if the vncserver starts automatically.

pi@myrpi:~ $ sudo reboot

I sourced most of the content from the following link but some of the steps there didn’t work out of the box so I modified them and wrote a new post for my knowledge.


C++ Utility function for converting bytes to higher units

Sometimes you need a handy function to convert number of bytes to a human readable size. I wrote a C++ version but found better logic on StackOverflow but implemented in C so decided to implement a similar function in C++.

*Function to convert number of bytes to higher units.
*Inspired from C version of source from:


#define LIST_SZ(x) (sizeof(x)/sizeof(*(x)))

static const char *units[] = { "TiB", "GiB", "MiB", "KiB", "B" };
static const unsigned long tebibytes = 1024ULL * 1024ULL * 1024ULL * 1024ULL;

HumanReadableSize(unsigned long bytes)
std::stringstream result;
unsigned long multiplier = tebibytes;

for (int i = 0; i < LIST_SZ(units); i++, multiplier /= 1024)
if (bytes < multiplier)
if (bytes % multiplier == 0)
result << (bytes / multiplier) << " " << units[i] << std::fixed;
result << std::setprecision(4) << ((float) bytes / multiplier) << " " << units[i];
return result.str();
result << "0";
return result.str();

//Unit Test function
int main(void)
unsigned long list[] =
0, 1, 2, 34, 900, 1023, 1024, 1025, 2048, 1024 * 1024,
1024 * 1024 * 1024 + 1024 * 1024 * 400

for (int i = 0; i < LIST_SZ(list); i++)
std::cout << HumanReadableSize(list[i]);
std::cout << std::endl;
std::cout << HumanReadableSize(2966141478);
return 0;

Best practices for obtaining GCOV code coverage for C/C++ application

Every now and then at work I come across the need to instrument a new project with code coverage and as it happens I end up struggling to recollect how I did it. Google does come to my rescue but most of the posts deal with how to instrument the code and process basic reports but none of them deal with best practices as such. So here is a TL;DR version of best practices according to my opinion which I plan to refer next time I need to do the task. My best practices are for the situation similar to what I’m facing and these need to be tweaked for other cases.

Rules of engagement:

  • Need to instrument C/C++ code
  • Work with standard GCC 4.4 compiler and the lcov-1.12  (These are the versions I’m using but other versions may work)
  • Target system where the binary is executed is different from the system where the source is compiled.
  • There are multiple versions of target devices where different code paths get executed
  • Need to generate a combined coverage report from all the target devices.
  • For this example, assume my work- space root is /home/jpadhye/project and source is contained in directories comp1 and comp2
  • For this example, the compiled are stored under work-space root in directory obj/x86_64

Steps for instrumentation:

1] If you are using GNU makefile, let’s assume it is you have lines:

$(BLDDIR): $(BLDDIR)/executable.bin
$(BLDDIR)/%.lo $(BLDDIR)/%.o $(BLDDIR)/ private OPT_CFLAGS = -O3
$(BLDDIR)/%.lo $(BLDDIR)/%.o: private EXTRA_CFLAGS = -fno-strict-aliasing
$(BLDDIR)/%.lo $(BLDDIR)/%.o: private ONLY_CXXFLAGS += -Woverloaded-virtual
$(BLDDIR)/%.lo $(BLDDIR)/%.o $(BLDDIR)/ private DEBUG_CFLAGS =

To instrument you can add extra items to enable code coverage optionally:

#Switch to turn coverage on
$(BLDDIR): $(BLDDIR)/executable.bin
$(BLDDIR)/%.lo $(BLDDIR)/%.o: private EXTRA_CFLAGS = --coverage
$(BLDDIR)/%.lo $(BLDDIR)/%.o: private EXTRA_CXXFLAGS = --coverage
$(BLDDIR)/%.lo $(BLDDIR)/%.o: private ONLY_CXXFLAGS = -fno-default-inline -fno-inline
$(BLDDIR)/%.lo $(BLDDIR)/%.o $(BLDDIR)/ private OPT_CFLAGS = -O0
$(BLDDIR)/%.lo $(BLDDIR)/%.o $(BLDDIR)/ private DEBUG_CFLAGS = -g
$(BLDDIR)/%.bin: private EXTRA_LDFLAGS += --coverage
$(BLDDIR)/ private SO_FLAGS += --coverage
$(BLDDIR)/%.lo $(BLDDIR)/%.o $(BLDDIR)/ private OPT_CFLAGS = -O3
$(BLDDIR)/%.lo $(BLDDIR)/%.o: private EXTRA_CFLAGS = -fno-strict-aliasing
$(BLDDIR)/%.lo $(BLDDIR)/%.o: private ONLY_CXXFLAGS += -Woverloaded-virtual
$(BLDDIR)/%.lo $(BLDDIR)/%.o $(BLDDIR)/ private DEBUG_CFLAGS =

The extra-define switch of -DTARGET_CODE_COVERAGE is to enable signal handling code in the instrumented target which you will add in next step.

2] Then add proper signal handlers to the source code:

/* Make sure proper headers are included*/
#include <signal.h>
#include <unistd.h>
/*Forward declaration of flush api*/
void __gcov_flush();
/*Signal handler definition which flushes profiling data when 
exit() and __gcov_flush() is called. */

void signal_handler(int signum)
  if (signo == SIGPROF) {
  	printf("Received SIGPROF\n");
  } else if (signo == SIGSTOP) {
   	  printf("received SIGSTOP\n");

//Main function of your program
int main ()
//Handle the signals	
if (signal(SIGPROF, sig_handler) == SIG_ERR)
	printf("\ncan't catch SIGKILL\n");
if (signal(SIGSTOP, sig_handler) == SIG_ERR)
    printf("\ncan't catch SIGSTOP\n");

3] Then compile your source code with code coverage enabled. Ensure that the $_TARGET_CODE_COVERAGE is set to 1 to enable code coverage. After the compilation is done, for all of the instrumented source files, you will find a *.gcno with the same name and under same  directory structure as the source file. In my case, the object files are collected in the ‘obj/x86_64’ directory in the work-space root with the source directory structure maintained.  These files are used while generating the coverage information. If these files are not created, then something went wrong in your instrumentation. Check the above steps

Steps for execution:

In my case, the target execution environment was a separate device, different than the device on which the code was built. So these steps are for my use case but are also applicable where build and execution machine are the same.

1] When the code gets compiled with code coverage enabled, the coverage file contain the full path. For example, if you work-space root directory is ‘/home/jaideep/project’ then the complete absolute file path for the source files gets recorded. When code gets executed on target machine, the *.gcda files containing the coverage information will be maintain the same directory and naming structure as the source files. But if you want the coverage information to be generated in a specific folder, then you need to strip the prefix of the work-space directory and specify alternate prefix for the work-space directory structure as follows:

export GCOV_PREFIX=/tmp/codecoverage/

This ensures that the directory structure from the project directory onward gets generated in the directory specified by GCOV_PREFIX.

2] Once the environment is set, then we execute the instrumented binary and run the required tests to generate the coverage information. Once you are done, you can kill the process with SIGSTOP which results in graceful execution of the program: ‘kill -SIGSTOP <pid>’. If you want to generate code coverage for each test case, then you can simply call  ‘kill -SIGPROF <pid>’ to make the process dump the coverage information without killing the processes itself. Any of these signals will result in coverage information being dumped in the form of *.gcda files with the same directory structure from the project root onward.

3] Once the coverage information is generated, compress the folder containing the *gcda files into a tarball and copy it to the root of your work-space.

cd /tmp/codecoverage/
tar -czf ${HOSTNAME}.tgz obj
scp ${HOSTNAME}.tgz ${TRGT}:${WKSP}

Generating HTML report:

To generate the HTML coverage report, ensure all the coverage information tarballs from your target devices are present. Currently my script handles information from two target hosts but the logic could be extended to handle multiple hosts. Following is the explanation of the script:

#host1_report.tgz: First variable is coverage tarball copied from first target device.
#host2_report.tgz: Second variable is coverage tarball copied from second target device.
#test_name: This will show up as the report name in the html report
#pattern: The pattern you are interested in. For example:If I only want coverage for comp1, I'll give '*/comp1/*'
#output_location: Location where html report is expected. This should be document directory of webserver.
./ target1-lnx.tgz target2-lnx.tgz lnx-app-ut1 '*/comp1/subdir/* */comp2/subdir/*' /var/www/htdocs/

The annotated script to generate the report is as follows:

#Run this script from the workspace root
set -o errexit
set -v
set -x

#Define temporary directory where coverage metadata will be stored.

#Parse the user input. This part taken from:

usage() {
  echo "Usage: $0 <host1_report.tgz> <host2_report.tgz> <test_name> <pattern> <output_location>"
  exit 1

[ -n "$1" ] || usage

[ -n "$1" ] || usage

[ -n "$1" ] || usage

[ -n "$1" ] || usage

[ -n "$1" ] || usage

#Create test title with timestamp
TITLE="${TEST_NAME}_$(date +"%m%d%y%H%M%S")"

echo "WORK_DIR: ${WORK_DIR}"
echo "HOST1: ${HOST1}"
echo "HOST2: ${HOST2}"
echo "TITLE: ${TITLE}"

#Cleanup the coverage directory and extract lcov tool
# and setup the PATH to the lcov binary
rm -rf ${WORK_DIR}
mkdir -p ${WORK_DIR}
wget -O ${WORK_DIR}/lcov-1.12.tar.gz
tar -xzf ${WORKDIR}/lcov-*.tar.gz -C ${WORK_DIR}/ --strip-components=1
export PATH=${WORK_DIR}/bin:$PATH

#Setup lcov options
# --no-external : Tells lcov to ignore paths outside work directory prefix
# --rc lcov_branch_coverage=1 : Turns on config option to generate branch coverage.
LCOV_OPTS="--no-external --rc lcov_branch_coverage=1" #--ignore-errors source

#Create initial coverage
lcov -c -i -t ${TITLE} -d ${PWD}/obj/x86_64/-o ${WORK_DIR}/coverage.initial

#Cleanup any previous *.gcda files and extract the edge report
find ${WORKDIR}/ -name "*.gcda" -exec rm -rf {} \;
tar -zxf ${HOST1_REPORT}
lcov -c -t ${TITLE} -b ${PWD} -d ${PWD}/obj/x86_64/ -o ${WORK_DIR}/${HOST1} ${LCOV_OPTS}

#Cleanup any previous *.gcda files and extract the core report
find ${PWD}/obj/x86_64/ -name "*.gcda" -exec rm -rf {} \;
tar -zxf ${HOST2_REPORT}
lcov -c -t ${TITLE} -b ${PWD} -d ${PWD}/obj/x86_64/ -o ${WORK_DIR}/${HOST2} ${LCOV_OPTS}

#Cleanup all the gcda files once reports are processed
find ${PWD}/obj/x86_64/ -name "*.gcda" -exec rm -rf {} \;

#Combine the host1 and host2 reports
lcov -t ${TITLE} -a ${WORK_DIR}/${HOST1} \
-a ${WORK_DIR}/${HOST2} -t ${TITLE} \
-a ${WORK_DIR}/coverage.initial -t ${TITLE} \
-o ${WORK_DIR}/${HOST1}_${HOST2} \

#Stop globbing so that pattern is not expanded in next line
set -f

#Extract the interesting pattern supplied by user from the combined report
lcov -e ${WORK_DIR}/${HOST1}_${HOST2} ${PATTERN} \

#Generate the HTML report with legend and branch coverage information
genhtml -t ${TITLE} -o ${OUTPUT_LOC}/${TITLE} -p ${PWD} \
${WORK_DIR}/${TITLE} --legend --branch-coverage --num-spaces 4

exit ${RETVAL}