Reiser4 on an inherently read-only block device

Hi Reiser developers,

Reiser4 is almost perfect for our (thinlinx.com's) needs except for one 
problem: it wants to write to the block device even when mounted 
read-only, and handles errors ungracefully (read as: crashes and burns) 
when it can't - specifically, when performing the umount operation.  I 
haven't been able to devise a simple reproducer for this, e.g. using a 
tiny ISO9660 filesystem, so there must be some subtleties that I am 
unaware of, but it happens 100% of the time when using our real data.

We have a couple of use cases that necessarily involve inherently 
read-only block devices:

1) We want to provide an ISO9660-based installer for our O/S that 
contains a Reiser4 (kinda-sorta-)root filesystem image that the 
installer would mount read-only via loopback to inspect certain files 
prior to dd'ing it to a target disk.

2) We want to share a copy of the Reiser4 (kinda-sorta-)root filesystem, 
which is mounted read-only on a writeable medium, read-only via the 
ATA-over-Ethernet protocol for use by network-booted instances of our 
O/S (this is feasible because the *real* root filesystem is AUFS with a 
couple of additional writeable layers).  The resulting /dev/etherd/eX.Y 
block device is inherently read-only - if it isn't, we risk write 
contention and Bad Things.

Unless I'm missing something, Reiser4 doesn't provide any mount option 
that would permit safe operation in the above use cases. Btrfs provides 
a "norecovery" a.k.a. "nologreplay" option that allows suppression of 
transaction log replay in situations in which the integrity of the 
filesystem is already guaranteed.  Is it possible to add a comparable 
mount option in Reiser4?  It seems to me that read-only should mean 
**read only**!

FYI we are using the latest Git state of 
https://github.com/edward6/reiser4 that compiles cleanly on a Linux 5.4 
kernel (commit 1a55b8ed6e0ac4de20135146d77bac4607d59fbe).

Regards,

Paul Whittaker (<[email protected]> or <[email protected]>),
ThinLinX Pty Ltd