Android Kernel Features

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List of Kernel features unique to Android

Binder

  • Binder - corba-like IPC
    • used instead of SysV IPC for interprocess communication
    • The Linux version of Binder was originally derived from a project by PalmSource to implement a CORBA-like message-passing or method invocation system. Documentation on that system is at: http://www.angryredplanet.com/~hackbod/openbinder/docs/html/index.html
    • implementation is at: drivers/android/binder.c, with include file include/linux/binder.h

ashmem

  • ashmem - Android shared memory
    • implementation is in mm/ashmem.c

According to the Kconfig help "The ashmem subsystem is a new shared memory allocator, similar to POSIX SHM but with different behavior and sporting a simpler file-based API."

Apparently it better-supports low memory devices, because it can discard shared memory units under memory pressure.

To use this, programs open /dev/ashmem, use mmap() on it, and can perform one or more of the following ioctls:

  • ASHMEM_SET_NAME
  • ASHMEM_GET_NAME
  • ASHMEM_SET_SIZE
  • ASHMEM_GET_SIZE
  • ASHMEM_SET_PROT_MASK
  • ASHMEM_GET_PROT_MASK
  • ASHMEM_PIN
  • ASHMEM_UNPIN
  • ASHMEM_GET_PIN_STATUS
  • ASHMEM_PURGE_ALL_CACHES

pmem

  • PMEM - Process memory allocator
    • implementation at: drivers/misc/pmem.c with include file at: include/linux/android_pmem.h


logger

  • logger - system logging facility
    • This is the kernel support for the 'logcat' command
    • The kernel driver for the serial devices for logging are in the source code drivers/android/logging.c
    • See Android logger for more information

wakelocks

  • wakelock - used for power management
    • Holds machine awake on a per-event basis until wakelock is released
    • See Android Power Management for detailed information

oom handling

  • oom handling modifications
    • lowmem notifications

alarm

  • alarm

paranoid network security

timed gpio

Generic gpio is a mechanism to allow programs to access and manipulate gpio registers from user space.

"Timed gpio" appears to be a system to allow for similar gpio manipulation, but with an added capability to automatically set a value in a gpio after a specified timeout.

On my ADP1, there is a driver at:

I'm not sure who uses this, or how it is used, but this is a directory with the following items:

# cd /sys/bus/platform/drivers/timed-gpio
# ls -l
--w-------    1 0        0            4096 Nov 13 02:11 bind
lrwxrwxrwx    1 0        0               0 Nov 13 02:11 timed-gpio -> ../../../../devices/platform/timed-gpio
--w-------    1 0        0            4096 Nov 13 02:11 uevent
--w-------    1 0        0            4096 Nov 13 02:11 unbind

Also, there is a device at:

# cd /sys/devices/platform/timed-gpio
# ls -lR
.:
lrwxrwxrwx    1 0        0               0 Nov 13 01:34 driver -> ../../../bus/platform/drivers/timed-gpio
-r--r--r--    1 0        0            4096 Nov 13 01:34 modalias
drwxr-xr-x    2 0        0               0 Nov 13 01:34 power
lrwxrwxrwx    1 0        0               0 Nov 13 01:34 subsystem -> ../../../bus/platform
-rw-r--r--    1 0        0            4096 Nov 13 01:34 uevent

./power:
-rw-r--r--    1 0        0            4096 Nov 13 01:34 wakeup

Possibly this means that one of the GPIO pins on the ADP1 is tied to a power wakeup event???

Kernel configuration options

The file Documentation/android.txt has a list of required configuration options for a kernel to support an Android system.

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