I am using card2 where I have  frozen btrfs file system due to raspberry pi kernel sources emerge.

Inserted on eow:

	eos /home/jlpoole # ls /dev/mmc* -lat
	brw-rw---- 1 root disk 179, 1 Sep 19 09:15 /dev/mmcblk0p1
	brw-rw---- 1 root disk 179, 2 Sep 19 09:15 /dev/mmcblk0p2
	brw-rw---- 1 root disk 179, 0 Sep 19 09:15 /dev/mmcblk0
	eos /home/jlpoole # 

eos /home/jlpoole # mount /dev/mmcblk0p1 /mnt/card2
eos /home/jlpoole # cat >/mnt/card2/cat_attempt_from_eos_202309190927.txt
test
eos /home/jlpoole # ls /mnt/card2/cat*
/mnt/card2/cat_attempt_from_eos_202309190927.txt
eos /home/jlpoole # sync
eos /home/jlpoole # touch /mnt/card2/touch_attempt_from_eos_202309190928.txt
eos /home/jlpoole # ls /mnt/card2/touch*
/mnt/card2/touch_attempt_from_eos_202309190928.txt
eos /home/jlpoole # sync
eos /home/jlpoole # umount /mnt/card2
eos /home/jlpoole # date
Tue Sep 19 09:28:54 PDT 2023
eos /home/jlpoole # mount /dev/mmcblk0p1 /mnt/card2
eos /home/jlpoole # ls /mnt/card2/touch*
ls: cannot access '/mnt/card2/touch*': No such file or directory
eos /home/jlpoole # ls /mnt/card2/cat*
ls: cannot access '/mnt/card2/cat*': No such file or directory
eos /home/jlpoole # umount /mnt/card2
eos /home/jlpoole # 
	eos /home/jlpoole # fdisk -l /dev/mmcblk0
	Disk /dev/mmcblk0: 59.48 GiB, 63864569856 bytes, 124735488 sectors
	Units: sectors of 1 * 512 = 512 bytes
	Sector size (logical/physical): 512 bytes / 512 bytes
	I/O size (minimum/optimal): 512 bytes / 512 bytes
	Disklabel type: dos
	Disk identifier: 0xdb97fc2a

	Device         Boot  Start       End   Sectors  Size Id Type
	/dev/mmcblk0p1 *      2048    524287    522240  255M  c W95 FAT32 (LBA)
	/dev/mmcblk0p2      524288 124735487 124211200 59.2G 83 Linux
	eos /home/jlpoole # 

See if I can write to FAT32 partition:

	eos /home/jlpoole # date
	Tue Sep 19 09:22:28 PDT 2023
	eos /home/jlpoole # mount /dev/mmcblk0p1 /mnt/card2
	eos /home/jlpoole # ls -lat /mnt/card2
	total 71688
	drwxr-xr-x 5 root root     4096 Sep 19 09:15 ..
	-rwxr-xr-x 1 root root     3081 Aug 19 18:08 startup.sh
	-rwxr-xr-x 1 root root     3021 Aug 19 17:59 autoexpand_root.sh
	-rwxr-xr-x 1 root root        0 Aug 19 16:08 ssh
	-rwxr-xr-x 1 root root     1878 Aug 19 15:17 config.txt
	-rwxr-xr-x 1 root root      162 Aug 19 01:24 cmdline.txt
	drwxr-xr-x 2 root root    24576 Aug 18 01:07 overlays
	-rwxr-xr-x 1 root root    30119 Aug 18 01:06 bcm2710-rpi-2-b.dtb
	-rwxr-xr-x 1 root root    32482 Aug 18 01:06 bcm2710-rpi-3-b-plus.dtb
	-rwxr-xr-x 1 root root    31871 Aug 18 01:06 bcm2710-rpi-3-b.dtb
	-rwxr-xr-x 1 root root    30106 Aug 18 01:06 bcm2710-rpi-cm3.dtb
	-rwxr-xr-x 1 root root    31179 Aug 18 01:06 bcm2710-rpi-zero-2-w.dtb
	-rwxr-xr-x 1 root root    31179 Aug 18 01:06 bcm2710-rpi-zero-2.dtb
	-rwxr-xr-x 1 root root    51955 Aug 18 01:06 bcm2711-rpi-4-b.dtb
	-rwxr-xr-x 1 root root    52087 Aug 18 01:06 bcm2711-rpi-400.dtb
	-rwxr-xr-x 1 root root    52540 Aug 18 01:06 bcm2711-rpi-cm4.dtb
	-rwxr-xr-x 1 root root    49870 Aug 18 01:06 bcm2711-rpi-cm4s.dtb
	-rwxr-xr-x 1 root root    20912 Aug 18 01:06 bcm2837-rpi-3-a-plus.dtb
	-rwxr-xr-x 1 root root    21777 Aug 18 01:06 bcm2837-rpi-3-b-plus.dtb
	-rwxr-xr-x 1 root root    21313 Aug 18 01:06 bcm2837-rpi-3-b.dtb
	-rwxr-xr-x 1 root root    20640 Aug 18 01:06 bcm2837-rpi-cm3-io3.dtb
	-rwxr-xr-x 1 root root 24003072 Aug 18 01:06 kernel8-p4.img
	-rwxr-xr-x 1 root root 22385152 Aug 18 01:06 kernel8.img
	-rwxr-xr-x 1 root root  4177063 Aug 17 23:56 initramfs-2.0.0.cpio.gz
	-rwxr-xr-x 1 root root    52476 Aug 17 15:39 bootcode.bin
	-rwxr-xr-x 1 root root     7265 Aug 17 15:39 fixup.dat
	-rwxr-xr-x 1 root root     5398 Aug 17 15:39 fixup4.dat
	-rwxr-xr-x 1 root root     3170 Aug 17 15:39 fixup4cd.dat
	-rwxr-xr-x 1 root root     8382 Aug 17 15:39 fixup4db.dat
	-rwxr-xr-x 1 root root     8386 Aug 17 15:39 fixup4x.dat
	-rwxr-xr-x 1 root root     3170 Aug 17 15:39 fixup_cd.dat
	-rwxr-xr-x 1 root root    10229 Aug 17 15:39 fixup_db.dat
	-rwxr-xr-x 1 root root    10229 Aug 17 15:39 fixup_x.dat
	-rwxr-xr-x 1 root root  2975104 Aug 17 15:39 start.elf
	-rwxr-xr-x 1 root root  2250848 Aug 17 15:39 start4.elf
	-rwxr-xr-x 1 root root   805436 Aug 17 15:39 start4cd.elf
	-rwxr-xr-x 1 root root  3747240 Aug 17 15:39 start4db.elf
	-rwxr-xr-x 1 root root  2998344 Aug 17 15:39 start4x.elf
	-rwxr-xr-x 1 root root   805436 Aug 17 15:39 start_cd.elf
	-rwxr-xr-x 1 root root  4819144 Aug 17 15:39 start_db.elf
	-rwxr-xr-x 1 root root  3721992 Aug 17 15:39 start_x.elf
	-rwxr-xr-x 1 root root        0 Dec 31  1979 dont_autoexpand_root
	drwxr-xr-x 3 root root    16384 Dec 31  1969 .
	eos /home/jlpoole # touch /mnt/card2/eos_touched_202309190923.txt
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole # mount /dev/mmcblk0p1 /mnt/card2
	eos /home/jlpoole # ls -lat /mnt/card2/eos*
	ls: cannot access '/mnt/card2/eos*': No such file or directory
	eos /home/jlpoole # ls -lat /mnt/card2/boot*
	-rwxr-xr-x 1 root root 52476 Aug 17 15:39 /mnt/card2/bootcode.bin
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole # date
	Tue Sep 19 09:24:39 PDT 2023
	eos /home/jlpoole # 

	eos /home/jlpoole # mount /dev/mmcblk0p1 /mnt/card2
	eos /home/jlpoole # cat >/mnt/card2/cat_attempt_from_eos_202309190927.txt
	test
	eos /home/jlpoole # ls /mnt/card2/cat*
	/mnt/card2/cat_attempt_from_eos_202309190927.txt
	eos /home/jlpoole # sync
	eos /home/jlpoole # touch /mnt/card2/touch_attempt_from_eos_202309190928.txt
	eos /home/jlpoole # ls /mnt/card2/touch*
	/mnt/card2/touch_attempt_from_eos_202309190928.txt
	eos /home/jlpoole # sync
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole # date
	Tue Sep 19 09:28:54 PDT 2023
	eos /home/jlpoole # mount /dev/mmcblk0p1 /mnt/card2
	eos /home/jlpoole # ls /mnt/card2/touch*
	ls: cannot access '/mnt/card2/touch*': No such file or directory
	eos /home/jlpoole # ls /mnt/card2/cat*
	ls: cannot access '/mnt/card2/cat*': No such file or directory
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole # 

	eos /home/jlpoole # man fsck
	eos /home/jlpoole # date
	Tue Sep 19 09:32:01 PDT 2023
	eos /home/jlpoole # fsck -y /dev/mmcblk0p1
	fsck from util-linux 2.38.1
	eos /home/jlpoole # fsck -y /dev/mmcblk0p2
	fsck from util-linux 2.38.1
	eos /home/jlpoole # 

	eos /home/jlpoole # mount /dev/mmcblk0p2 /mnt/card2
	eos /home/jlpoole # date; time btrfs rescue zero-log  /mnt/card2
	Tue Sep 19 09:35:25 PDT 2023
	ERROR: not a regular file or block device: /mnt/card2
	ERROR: could not open ctree

	real	0m0.002s
	user	0m0.001s
	sys	0m0.000s
	eos /home/jlpoole # ls -la /mnt/card2/home
	total 16
	drwxr-xr-x 1 root    root   30 Aug 19 11:08 .
	drwxr-xr-x 1 root    root  126 Aug 17 18:08 ..
	drwxr-xr-x 1 jlpoole users  64 Aug 17 16:46 demouser
	drwxr-xr-x 1    1001  1001 334 Sep 10 08:54 jlpoole
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole # date; time btrfs rescue zero-log  /dev/mmcblk0p2
	Tue Sep 19 09:36:22 PDT 2023
	Clearing log on /dev/mmcblk0p2, previous log_root 0, level 0

	real	0m0.030s
	user	0m0.003s
	sys	0m0.000s
	eos /home/jlpoole # mount /dev/mmcblk0p2 /mnt/card2
	eos /home/jlpoole # touch /mnt/card2/eos_touch_20230919_0937.txt
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole # mount /dev/mmcblk0p2 /mnt/card2
	eos /home/jlpoole # ls -la /mnt/card2/eo*
	ls: cannot access '/mnt/card2/eo*': No such file or directory
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole # date; time btrfs rescue zero-log  /dev/mmcblk0p1
	Tue Sep 19 09:38:49 PDT 2023
	No valid Btrfs found on /dev/mmcblk0p1
	ERROR: could not open ctree

	real	0m0.021s
	user	0m0.002s
	sys	0m0.000s
	eos /home/jlpoole # # above duly aborts since p1 is FAT
	eos /home/jlpoole # date
	Tue Sep 19 09:39:21 PDT 2023
	eos /home/jlpoole # mount /dev/mmcblk0p1 /mnt/card2
	eos /home/jlpoole # touch /mnt/card2/eos_touch_20230919_0939.txt
	eos /home/jlpoole # ls /mnt/card2/eos* -la
	-rwxr-xr-x 1 root root 0 Sep 19 09:40 /mnt/card2/eos_touch_20230919_0939.txt
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole # mount /dev/mmcblk0p1 /mnt/card2
	eos /home/jlpoole # ls /mnt/card2/eos* -la
	ls: cannot access '/mnt/card2/eos*': No such file or directory
	eos /home/jlpoole # umount /mnt/card2
	eos /home/jlpoole #