[Galaxy Tab 2 7" Android Development] DivinityCycle:
Hey guys.

Some previous Samsung devices had no external storage at all but still mapped the biggest flash partition to /mnt/sdcard.

The Galaxy Tab 2 7.0 has a Micro SD card slot on it (one of the reasons I bought the thing!), but I guess for compatibility they still mount an internal flash storage partition to /sdcard. The actual micro SD card gets mounted to freaking /mnt/extSdCard.

Why does this matter?

Basically, tons of stuff in Android is setup to dump the large files to /sdcard by default. Things like games that require an extra download, the Camera app, etc. I've got a 32GB microSD card in there, and it makes me really frustrated that stuff won't just automatically use that.

So. What I'm looking to do is switch them around, so the internal fake flash partition ends up mounting to /mnt/extSdCard and the REAL microSD card mounts to /mnt/sdcard. That way my big huge card is where most data will end up automagically. Ultimately if I could just dump the internal "sdcard" partition and give that space to other parts of the system, that'd be sweet, but at this point I'm still kindof in la la land with Android, so I'll be happy just to get the mounts flipped around.

I do Linux stuff for work, and use a 5-disk file server at home running Ubuntu Server, so I approached this problem in a Linux way: why not mount via fstab??

Turns out Android doesn't actually directly have a /etc/fstab. Instead you've got /system/etc/vold.fstab.

From my brief research, this file appears to work pretty much the same way as fstab in Linux.

However, the stock one doesn't contain any mountpoint for the fake internal sdcard. vold.fstab seems to tell the vold executable what to do during boot-time.

My first problem: the vold.fstab file on my device doesn't contain any mount instructions for the /sdcard device.

Not a problem, I have SSH and WinSCP working, so I got a read on the mount points likeso:

127|root@android:/dev/block # cat /proc/mounts
rootfs / rootfs ro,noatime 0 0
tmpfs /dev tmpfs rw,nosuid,noatime,mode=755 0 0
devpts /dev/pts devpts rw,noatime,mode=600 0 0
proc /proc proc rw,noatime 0 0
sysfs /sys sysfs rw,noatime 0 0
none /acct cgroup rw,noatime,cpuacct 0 0
tmpfs /mnt/asec tmpfs rw,noatime,mode=755,gid=1000 0 0
tmpfs /mnt/obb tmpfs rw,noatime,mode=755,gid=1000 0 0
none /dev/cpuctl cgroup rw,noatime,cpu 0 0
/dev/block/platform/omap/omap_hsmmc.1/by-name/FACTORYFS /system ext4 ro,noatime,barrier=1,data=ordered 0 0
/dev/block/platform/omap/omap_hsmmc.1/by-name/DATAFS /data ext4 rw,nosuid,nodev,noatime,barrier=1,data=ordered,noauto_da_alloc,discard 0 0
/dev/block/platform/omap/omap_hsmmc.1/by-name/CACHE /cache ext4 rw,nosuid,nodev,noatime,errors=panic,barrier=1,nomblk_io_submit,data=ordered 0 0
/dev/block/platform/omap/omap_hsmmc.1/by-name/EFS /efs ext4 rw,noatime,barrier=1,data=ordered 0 0
/sys/kernel/debug /sys/kernel/debug debugfs rw,noatime 0 0
/dev/fuse /mnt/sdcard fuse rw,nosuid,nodev,noatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0
/dev/block/vold/179:25 /mnt/extSdCard vfat rw,dirsync,nosuid,nodev,noexec,noatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0

OK. so the vold.fstab file contains:

## Vold 2.0 Generic fstab
## - San Mehat (san@android.com)
##

#######################
## Regular device mount
##
## Format: dev_mount <label> <mount_point> <part> <sysfs_path1...>
## label - Label for the volume
## mount_point - Where the volume will be mounted
## part - Partition # (1 based), or 'auto' for first usable partition.
## <sysfs_path> - List of sysfs paths to source devices
######################

# external sdcard
dev_mount sdcard /mnt/extSdCard auto /devices/platform/omap/omap_hsmmc.0/mmc_host/mmc1

#usb host device
dev_mount usbdisk /mnt/usbdisk auto /devices/platform/omap/musb-omap2430/musb-hdrc/usb1

So, I have made a backup of my vold.fstab file, but I'm a little gun shy about making changes to it, particularly adding a new line for the "internal" sdcard. I know there are a couple of other ways to probably do this, like an init.d shell script that just executes the needed mount commands, and I'm honestly not sure if putting an entry for /mnt/sdcard into vold.fstab will override the mounts that are (I guess?) coming from the ramdisk init sequence. Any input, XDA devs?