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multirom: Fix /data/media/0 media linkage for SDCardFS #11

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@AdrianDC AdrianDC commented May 22, 2017

  • In a MultiROM environment, /data is owned by the
    booted secondary ROM, specifically it can even be
    part of an external MicroSD (for example with EXT4)

  • By using a ROM supporting SDCardFS, the interal
    media storage will be accessed through its driver,
    but the fact /data/media/0 could be used under
    specific conditions means the /data/media mounts
    used by the emulated storage loop through:

    • /data/media (external ROM)
    • /data/media/0 (internal storage)
  • SDCardFS prevents "cross-device" linkage by
    returning -EXDEV, breaking internal storage access

  • Always use the proper /data/media path on newer APIs
    to avoid any cross-device linkage of internal storage,
    and preserve old handling up to API 22 (Android 5.1)

Change-Id: Ib49db68eede289d3943b9537d542eef5082e3118
Signed-off-by: Adrian DC radian.dc@gmail.com

 * In a MultiROM environment, /data is owned by the
    booted secondary ROM, specifically it can even be
    part of an external MicroSD (for example with EXT4)

 * By using a ROM supporting SDCardFS, the interal
    media storage will be accessed through its driver,
    but the fact /data/media/0 could be used under
    specific conditions means the /data/media mounts
    used by the emulated storage loop through:
     - /data/media (external ROM)
     - /data/media/0 (internal storage)

 * SDCardFS prevents "cross-device" linkage by
    returning -EXDEV, breaking internal storage access

 * Always use the proper /data/media path on newer APIs
    to avoid any cross-device linkage of internal storage,
    and preserve old handling up to API 22 (Android 5.1)

Change-Id: Ib49db68eede289d3943b9537d542eef5082e3118
Signed-off-by: Adrian DC <radian.dc@gmail.com>
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