Fwiw, the limitation is not an issue of running in Dalvik vs. native code, but the permissions / uid an application is running as. Third party apps can not run with permissions to be able to do this kind of stuff.
On Fri, Jan 14, 2011 at 9:07 AM, Hari Edo <hari....@gmail.com> wrote: > > > On Jan 14, 1:32 am, Saj TK <saj.dr...@gmail.com> wrote: > > Well, what i really wanted to do is delete the Media file from the memory > > location and write some encrypted data to the same location. I have to > make > > sure that i m writing to the same location, not anywhere else in the > card. > > To do this task on the removable SD card memory, you would need to > unmount > the filesystem, read some sectors of the filesystem directly to > determine where > the files are located, and write new data to the same sectors > directly. > > I am pretty sure that none of this is do-able within Java/Android code > on the > dalvik VM. It would be fairly straightforward as a native Linux > process, but you > generally need the root of the device to create such processes, > especially > if other programs have access to the SD flash memory you are trying to > unmount. > > It would be even harder to do this on the internal (system) memory, > because > it is where the system itself is stored, so unmounting it would > basically > require a specialized kernel or kernel module that could stay in RAM > during > the operation. > > This sounds like a security type of application. You mention > encryption, as > though you're replacing a file with its own encrypted contents. Of > course, a > bunch of random bytes in the same sectors would work as a secure > shredder. > > However, SD flash memory is not all built alike, and even direct > sector access > is not enough to guarantee you have made the files unrecoverable. > > Media security is a devilishly complicated topic, and many people > convince > themselves they can do it effectively while many others find glaring > loopholes > that bypass the implementation easily. > > Good luck on your endeavor. I think you have a steep uphill > challenge. > > -- > You received this message because you are subscribed to the Google > Groups "Android Developers" group. > To post to this group, send email to android-developers@googlegroups.com > To unsubscribe from this group, send email to > android-developers+unsubscr...@googlegroups.com<android-developers%2bunsubscr...@googlegroups.com> > For more options, visit this group at > http://groups.google.com/group/android-developers?hl=en > -- Dianne Hackborn Android framework engineer hack...@android.com Note: please don't send private questions to me, as I don't have time to provide private support, and so won't reply to such e-mails. All such questions should be posted on public forums, where I and others can see and answer them. -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
