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I am doing away with exFat for my Microsd card after all my pictures decayed , corrupted and the directory was locked. I cant seem to write into a specific directory. chkdsk will just plain abort saying :

The disk does not have enough space to replace bad clusters
detected in file \WhatsApp\.Shared of name 1.
Corruption was found while examining files in directory \WhatsApp\ (6).


so I 'd like give a shot to Ext4 partitioning that cheap micro sd card , not just 2 ( the standard app2sd and sdcard1 design ) but 3. One for apps and other 2 depending on the write activity , I tweaked the block parameters etc. for each
I am able to mount the partitions & a rooted Total Commander can see them all BUT other apps cannot see the partitions I created.As I understand vold helps other apps be aware of this. So How do I go about getting this 'formally' with sounding 'hackish'
what I did :

mkdir /storage/<my dir>
mount -t ext4 -o noatime,rw /dev/block/mmcblk(x)p(y) /storage/<my dir>
where x and y are variables from partitions file in the proc dir.

I read about a fstab.<phonename> file out there that can be modified but it would be overwritten every boot.

even the 2nd partition that app2sd ( or link2sd) creates can ONLY be approached as root. So prolly those apps that ask for root can see this stuff but other apps can write to it
Ext4 is linux . Sounds like Android seems to ignore its own 'biological' kid ext4 and instead recognize a stepson 'exfat / FAT '
I am sure I am missing something here. Any ideas ?
I am rooted with Magisk on a Galaxy j7 with of course TWRP ( 3.x) installed

Print env o/p Mount o/p

user1874594
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  • BUT other apps cannot see the partitions. Even with root access? Make sure this isn't because of Mount Namespace: https://android.stackexchange.com/a/200449/218526. Vold exposes only first partition on sdcard to apps. Try vold-posix if yours doesn't support Ext4. Directly writing to SD cards is restricted since KK or even before. Access you get is through SAF. Also may use bindfs (FUSE) to modify permissions of mountpoints so that apps can read the partitions, even from within /sdcard possibly (never tested though). – Irfan Latif Jul 13 '19 at 21:45
  • Ok just to clarify. app2sd Mount script puts script in magsik folder. On my phone magisk is at /sbin/magisk folder and I modified that manually to add the same logic now 2X more times for each additional partition. Strangely after I modified the script . After boot 2nd part & apps never showed up. I ran it manually and they all showed up . Also under TC I could see the additonal mount pts under /storage showing up as drives. Nothing changed AFAIK but now TC looks weird - all those Drives disappeared. After running script these pts under /storage will still be seen & su - TC can see it. – user1874594 Jul 13 '19 at 22:14
  • Coming to 2 other Q's from Irfan .Lot of common apps wont request root access. I cant force em & they cant see these even if I invoke TC. By going to TC I can see all of them under /storage but invoking TC via System share - everything disappears. Your other Q Magisk is get to global namespace yes. That was the setting hitherto . HTH – user1874594 Jul 13 '19 at 22:18
  • Also my partitions are like these mmcblk1p1--> App2sd second partition – user1874594 Jul 13 '19 at 22:19
  • Also my partitions are like these mmcblk1p1--> App2sd second partition mmcblk1p2 user data part # 1 , p3 user data part # 2 ,- all Ext4. If vold exposes just 1st Part, how do I go about getting the other 2 "exposed" ?. How do I get vold-posix working. How do I use FUSE . My parts are under /storage and earlier like I mentioned they got 'picked up' & could be seen as separate drives .in TC . Now they show as folders ( mounted ) under /storage . When the former situation existed I am not sure if apps could not access those ( prolly could .. my gallery app did , – user1874594 Jul 13 '19 at 22:25
  • not sure what caused the change of mind from separate drives .in TC to folders ( mounted ) under /storage. I know at that time app2sd use to give some alerts some of the apps are not mounted correctly should - use the advanced op to recreate mount script --> click Y --> reboot. I wonder if at that time it moved the mount script location / – user1874594 Jul 13 '19 at 22:28
  • post the output of mount and printenv somewhere (pastebin) after mountscript – alecxs Jul 14 '19 at 02:50
  • I dont see any place where I can paste the full o/p due to restrictions in #chars so I attached screenshots. Need to see that mount @ 300% I was able to read some - the file gets toned down in size & quality even if < 2mb ( max allowed ) – user1874594 Jul 14 '19 at 21:55
  • see pics attached – user1874594 Jul 14 '19 at 21:55
  • from mount what i can see your first partition is mounted twice. from printenv i can see you have knox? – alecxs Jul 14 '19 at 23:23
  • Knox is disabled or removed. Prolly 1st – user1874594 Jul 15 '19 at 01:08

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