Wrong id and gid running /system/bin/sdcard I am trying to use my ext4 sdcard properly in Stock rooted Android 4.4.4.
For this, I run 

mount -rw -t ext4 /dev/block/mmcblk1p1 /mnt/media_rw/sdcard1


and then

/system/bin/sdcard -u 1023 -g 1023 -w 1023 /mnt/media_rw/sdcard1 /storage/sdcard1


I also tried

/system/bin/sdcard /mnt/media_rw/sdcard1 /storage/sdcard1 1023 1023


The problem is that the ownership of the tree created in /storage/sdcard1 is then 0.1015 instead of 1023.1023 (??), so I have permission problems...

Any idea why the /system/bin/sdcard command is not obeying the ownership flags?

Thanks!
Edit:
The solution is here: https://source.android.com/devices/storage/config.html


  "For Android releases 4.3 and later, the various fstab files used by
  init, vold and recovery were unified in the /fstab. file. For
  external storage volumes that are managed by vold, the entries should
  have the following format:"


 &lt;src&gt; &lt;mnt_point&gt; &lt;type&gt; &lt;mnt_flags&gt; &lt;fs_mgr_flags&gt;



  "...Devices may provide external storage by emulating a
  case-insensitive, permissionless filesystem backed by internal
  storage. One possible implementation is provided by the FUSE daemon in
  system/core/sdcard, which can be added as a device-specific init.rc
  service:"


# virtual sdcard daemon running as media_rw (1023)
service sdcard /system/bin/sdcard &lt;source_path&gt; &lt;dest_path&gt; 1023 1023
    class late_start