Android - Read "device attribute" fails with error "invalid length" - android

I am working on the TI OMAP platform with Android as the operating system. For one UseCase, we have to toggle one of the LED's in the device. The LED has number of "Device Attributes" and from the Application Layer [.java], we want to read a "Device Attribute".
When we do run the cat command on the adb prompt:
# cat /sys/devices/device_name/device_attribute
# device_attribute:invalid length
We get the error "invalid length". Hence, I wanted to know is there a way to read a "Device Property" such that it is accessible to the App Layer as well.
I found a similar question on another forum http://android.modaco.com/topic/312770-possible-solution-for-lack-of-notification-light-developers-needed but it was also unanswered.
Thanks for the replies !!!
Solution
The device was only having "set_device_attribute" but since "get_device_attribute" was missing, we were getting "invalid length" issue when "read" command to that device property was issued.
I added a new API named:
static ssize_t get_device_attribute(struct device *dev, struct device_attribute *attr,
char *buf)
{
.........................
.........................
.........................
}
and updated the device attribute
static DEVICE_ATTR(device_property, 0777,get_device_attribute, set_device_attribute);

invalid length often indicates a directory. Try to cd into the last "device_attribute".
Alternativeley you can also search for device info in "/proc".

You probably have the Linux kernel source code,
search the particular sysfs implementation of the device, see how it was programmed.

Related

`arc` fails to parse appium.txt file, failing out at the first line

I'm trying to set up a local test rig for Appium before trying some cloud services. I've got the Appium.app running locally and have put together a very small test script in Ruby (using xpath). I'm trying to utilize arc (the Appium Ruby Console) to do some further scripting but am having trouble getting it launched. I've got everything installed (appium_lib, appium_console) and best I can tell it should be working. However, when I run the arc command at the terminal, I get the following error:
Failed to match sequence (ALL_SPACE (TABLE / TABLE_ARRAY / KEY_VALUE / COMMENT_LINE){0, } ALL_SPACE) at line 1 char 1.
`- Don't know what to do with "[caps]\n " at line 1 char 1.
Here are the contents of my appium.txt as of now.
[caps]
appium-version: '1.0',
platformName: 'Android',
platformVersion: '4.4',
deviceName: 'Nexus_5_API_22_Lollipop',
app: '/Users/justinr/Desktop/Development/TMSampleAndroid-master/app-debug.apk',
appPackage => 'com.marketlytics.calabashtest',
appActivity => 'com.marketlytics.calabashtest.MainActivity'
Thanks a ton in advance for any insight - please let me know if there are other useful files to see.
Running the arc setup android got this working for me (it stumps an appium.txt in the current directory). Still not sure what the problem with my original file was, though - I can't see any key differences.

Linux Kernel Dynamic Debug settings - persist across a reset

With Dynamic Debugging enabled in the Linux Kernel, I am able to control which prints show up by writing to /sys/kernel/debug/dynamic_debug/control. However, It seems that a reboot resets this file to its default settings (all prints disabled).
Is there a way to make the settings persist across a reset? I have a print which is emitted early in the boot process, and I am not able to get it to print, because the reboot disables this print in /sys/kernel/debug/dynamic_debug/control.
You should be able to add dyndbg='your query here' to the kernel command line using the bootloader configuration or manual options entry feature. This will vary with the bootloader although grub is the most common one
If you are using grub as a bootloader you would have to add it to the kernel command line in /boot/grub/grub.conf for the particular kernel you are launching at bootup.
A blog article about this can be found here. In particular it gives this example:
dyndbg='module xhci_hcd +p'
The article also discusses modifying grub as well.
This kernel howto about dynamic debugging has useful information about dyndbg. This section applies
To activate debug messages for core code and built-in modules during
the boot process, even before userspace and debugfs exists, use
dyndbg="QUERY", module.dyndbg="QUERY", or ddebug_query="QUERY"
(ddebug_query is obsoleted by dyndbg, and deprecated). QUERY follows
the syntax described above, but must not exceed 1023 characters. Your
bootloader may impose lower limits.
These dyndbg params are processed just after the ddebug tables are
processed, as part of the arch_initcall. Thus you can enable debug
messages in all code run after this arch_initcall via this boot
parameter.
On an x86 system for example ACPI enablement is a subsys_initcall and
dyndbg="file ec.c +p"
will show early Embedded Controller transactions during ACPI setup if
your machine (typically a laptop) has an Embedded Controller.
PCI (or other devices) initialization also is a hot candidate for using
this boot parameter for debugging purposes.
If foo module is not built-in, foo.dyndbg will still be processed at
boot time, without effect, but will be reprocessed when module is
loaded later. dyndbg_query= and bare dyndbg= are only processed at
boot.
You can do it as a part of post boot script. Say after Android boots(since i see Android tag added here), it runs certain sh scripts as a part of init procedure. Modify the sh files with the dynamic debug commands added and push it in and reboot .
Refer here for post boot script files info.
https://android.stackexchange.com/questions/6558/how-can-i-run-a-script-on-boot
You can have dynamic_debug for some kernel module foo activated automatically during boot using the /etc/modprobe.d/ directory.
### BEGIN prerequisite
# in case module "foo" is not yet automatically loaded during boot,
# then make it load during boot:
# create a file /etc/modules-load.d/foo.conf with contents "foo"
echo "foo" | sudo tee /etc/modules-load.d/foo.conf
### END prerequisite
# create a configuration file to activate dynamic debug for module "foo"
# at its "module initialization time"
echo "options foo dyndbg=+p" | sudo tee /etc/modprobe.d/foo.conf
Reference: Debug Messages at Module Initialization Time from kernel.org documentation.

Libgit2 running on Android unable to perform clone operation - returns "failed to set permissions" error

I have just built Libgit2 (v0.20.0) for Android (target SDK version 18, debugging on a rooted device running Cyanogenmod 10.1.2, Android 4.2.2) and a simple function like getting the version number of Libgit2 works fine through the JNI. But when I use the git_clone function it stops right after the objects/info folder is created and returns this error:
Error -1 cloning repository - Failed to set permissions on '/storage/sdcard0/it/ptt/.git/objects/info': Operation not permitted
I have given the application the WRITE_EXTERNAL_STORAGE permission but I guess it still can't chmod unless owner of the file. When I use adb shell to check out the permission mode of the info folder I get:
d---rwxr-x system sdcard_rw 2014-05-15 09:31 info
And by using pwd.h functions I get the username that the c code (that is calling git_clone) is under to be u0_a92. How am I suppose to get pass this I suppose very Android related issue? Is there a simple way to stop Libgit2 from calling p_chmod or can I give it permissions to do so?
I ended up defining p_chmod as a method always returning true to get passed the error. In the bash script I use to build libgit2 I inserted the following lines that leaves the source files in an unmodified condition after building for android:
LIBGIT2_POSIX_PATH="$LIBGIT2_SOURCE_PATH/src/posix.h"
LIBGIT2_POSIX_BACKUP_PATH="$LIBGIT2_SOURCE_PATH/src/posix_original.h"
printf "#include \"always_success.h\"\nint always_success() { return 0; }" > "$LIBGIT2_SOURCE_PATH/src/always_success.c"
printf "int always_success();" > "$LIBGIT2_SOURCE_PATH/src/always_success.h"
cp $LIBGIT2_POSIX_PATH "$LIBGIT2_POSIX_BACKUP_PATH"
sed -i "s/^#define\sp_chmod(p, m).*$/#include \"always_success.h\"\n#define p_chmod(p, m) always_success()\nextern int always_success();\n/" $LIBGIT2_POSIX_PATH
# run the build process with cmake ...
# restore chmod manipulated source header
mv $LIBGIT2_POSIX_BACKUP_PATH $LIBGIT2_POSIX_PATH
There is probably a cleaner way to solve this but at least now I dont get that error anymore. Thanks to Carlos for his help!
UPDATE
Running adb shell mount | grep sdcard I could see that the sdcard which I am trying to clone the repository into uses the vfat file system which according to this forum thread doesn't support unix-style permissions.

Retrieve Logcat data through native (C) code

I was wondering if there is any way to access the logcat logging data from native code ?
Also if someone knows what kind of shell can be accessed on the native linux system directly on the device itself (so NOT by starting a shell through adb on a client pc !!!) ?
Thanks in advance
You can either read the raw data fom /dev/log/main or you can run the built-in shell command logcat and pipe the result to a file descriptor as usual. The logcat command is usually preferably because then the printout is easier to filter and format.
As for the built-in shell, it is called toolbox and the source can be found in the Android open source project. The shell is rather similar to bash. Toolbox contains lots more functionality than just a shell. It is very similar to Busybox, but released under another license.
You can set it up using a log tag in your source file and then include the library as so:
#define LOG_TAG "some.unique.identifier" //I usually use the class name
#include <utils/Log.h>
Then in the Android.mk file you will need to add the liblog library dependency to your LOCAL_SHARED_LIBRARIES.
LOCAL_SHARED_LIBRARIES += liblog
Also, take note that logcat looks for the LOG_TAG definition to include as part of the tagging so it makes searching for your logs easier. Then you can log as such:
int my_int = 0;
ALOGI("some logs.... print my int: %d", my_int);
ALOGI is for info, you can also use ALOGE, ALOGD, ALOGV and ALOGW for error, debug, verbose and warning logging, respectively.
ALOG* is analogous to printf. I interchange them at times if I need to debug on different platforms, say Linux.

Froyoporting, vendor & device folder, and build for a device with tapas

i try to build Froyo for a given dev board, but i don't know how to configure the source tree, especially where should put the board specific code and the board configuration mkf ile, either in vendor or device ?
I first put my board specific code and config file in the vendor folder as:
vendor\cpyname\the_product_1\, with BoardConfig.mk that describe my board configuration.
I then have vendor\cpyname\product\ with the_product_1.mk to start the source tree build.
can't build with tapas, when giving product name (the_product_1), i get an error
build/core/product_configuration.mk
the_product_1 not found.
I also try with the device folder, like:
device\the_product_1\ with BoardConfig.mk,
and device\the_product_1\product\ with the_product_1.mk
tapas give the same result.
Note that first configuration can build and generate image with make PRODUCT-the_product_1-eng
I also personally find the build process quite obscure and missing documentation. Please help :)
Lionel
Froyo and the after use devices instead of vendor directory ,you will find sample there.

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