[eMMC] - Partition on eMMC boot block device is not visible anymore in kernel v6.1.53 and above

["Torrelli, Maxime" <Maxime.Torrelli@xxxxxxxxxxxx>]

Hello dear MMC community,

I hope my request does not break any rule regarding this mailing list and its use. If it does, please let me know how to proceed.

We recently tried to migrate from kernel v5.10 to v6.6. During this migration we discovered that a partition stored in an eMMC boot disk was not visible anymore from the system (i.e. /dev/mmcblk2boot0p1 does not exist).

Please find below the detailed list of block disks of the eMMC:
    * brw-rw---- 1 root disk 179,  0 Oct 10 17:41 /dev/mmcblk2
    * brw-rw---- 1 root disk 179,  8 Oct 10 17:40 /dev/mmcblk2boot0
    * brw-rw---- 1 root disk 179, 16 Oct 10 17:40 /dev/mmcblk2boot1
    * brw-rw---- 1 root disk 179, 24 Oct 10 17:40 /dev/mmcblk2gp0
    * brw-rw---- 1 root disk 179, 25 Oct 10 17:41 /dev/mmcblk2gp0p1
    * brw-rw---- 1 root disk 179, 32 Oct 10 17:40 /dev/mmcblk2gp1
    * brw-rw---- 1 root disk 179, 33 Oct 10 17:41 /dev/mmcblk2gp1p1
    * brw-rw---- 1 root disk 179,  1 Oct 10 17:41 /dev/mmcblk2p1
    * brw-rw---- 1 root disk 179,  2 Oct 10 17:41 /dev/mmcblk2p2
    * crw------- 1 root root 243,  0 Oct 10 17:41 /dev/mmcblk2rpmb

After analysis, we discovered the reason. When the version v6.1.53 was released, a change in file block/ioctl.c added the following lines to the function "blkpg_do_ioctl":
      > + if (disk->flags & GENHD_FL_NO_PART)
      > +      return -EINVAL;
This check was then moved to block/partitions/core.c when v6.1.76 was released. This change added the following lines in the function "bdev_add_partition" are :
      > + if (disk->flags & GENHD_FL_NO_PART) {
      > +      ret = -EINVAL;
      > +      goto out;
      > + }

With kernel v5.10 the partition /dev/mmcblk2boot0p1 was not visible at boot but a simple call to "partx -a /dev/mmcblk2boot0" allowed us to access this partition. With kernel v6.1.53 and above, "partx -a /dev/mmcblk2boot0" fails and we cannot access the partition.

What is the reason for this change ?

Is there any rule forbidding to create a partition in an eMMC boot block disk ?

Is there any way we can access this mmcblk boot partition with kernel v6.1.53 and above ? 

Thanks for your help !


Salutations/Greetings,
 
Maxime TORRELLI