Friday, October 7, 2011

Notes on the ASUS Transformer's file system / partition layout

rootfs on / type rootfs (rw,relatime)

# physical
/dev/block/mmcblk0p1 on /system type ext4 (ro,relatime,barrier=1,data=ordered,noauto_da_alloc)
/dev/block/mmcblk0p7 on /data type ext4 (rw,relatime,barrier=1,data=ordered,noauto_da_alloc)
/dev/block/mmcblk0p2 on /cache type ext4 (rw,nosuid,nodev,noatime,barrier=1,data=ordered)
/dev/fuse on /mnt/sdcard type fuse (rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other)

# special
tmpfs on /dev type tmpfs (rw,nosuid,relatime,mode=755)
devpts on /dev/pts type devpts (rw,relatime,mode=600)
proc on /proc type proc (rw,relatime)
sysfs on /sys type sysfs (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
none on /acct type cgroup (rw,relatime,cpuacct)
tmpfs on /mnt/asec type tmpfs (rw,relatime,mode=755,gid=1000)
tmpfs on /mnt/obb type tmpfs (rw,relatime,mode=755,gid=1000)
none on /dev/cpuctl type cgroup (rw,relatime,cpu)
tmpfs on /Removable type tmpfs (rw,relatime,mode=755,gid=1000)
/dev, /dev/pts, /proc, and /sys are normal Linux stuff. I'm not familiar with /dev/cpuctl or /sys/kernel/debug but they are fairly self explanitory! Whatever /mnt/asec, /mnt/obb, and /acct and numerous other things are explained briefly in /init.rc; poking around /acct is interesting. The tempfs on /Removable pretty much just serves as a place to put mount points for external media, i.e. MicroSD / SD cards and USB drives. The mmcblk device is clearly responsible for the most important parts of the Android system: /data and /system are your air and water. Under /data, you will pretty much find all your apps (stored on internal memory), and in /system, well, stuff that helps make your system work; d'uh. /system and /data can probably be looked at as read-only and read-write portions of the Android File System Hierachy, I guess. As far as mmcblk itself is concerned, it's just the internal memory card. The thing that I find rather interesting, is that the user storage area (/mnt/sdcard -> /sdcard), or what everyone typically interacts with, is provided through some type of relationship to FUSE, as opposed to directly through mmcblk0. This is curious enough to me, that I would consider poking around further, or even digging closer into ROMs for the Transformer, to be worth the effort. Yeah, I've just got to figure out how crap works, lol. On the upside, I know better than to disassemble my new "Stable" system and I'm to cheap to get one just for testing puposes.

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