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 (<paul@xxxxxxxxxxxx> or <pawhitt69@xxxxxxxxx>),
ThinLinX Pty Ltd
