Am 01.08.24 um 08:18 schrieb Johannes Bauer:
But my point is, that is what I am doing -- creating the losetup mapping
R/O:
# losetup --read-only --show -f image.img
/dev/loop35
# echo foo >/dev/loop35
bash: echo: write error: Operation not permitted
I.e., the block device is write protected and *yet* it changes content.
This is what I find so extremely puzzling, that the file system should
not have the capability to change the underlying block device, yet it does.
To expand on this, it also happens when I create a dmsetup linear
mapping that has been explicitly marked as read-only:
# dmsetup create --concise "linear,,2,ro,0 131072 linear /dev/loop28 0"
# md5sum image.img /dev/loop28 /dev/mapper/linear
56f56801923108d241947024926fea53 image.img
56f56801923108d241947024926fea53 /dev/loop28
56f56801923108d241947024926fea53 /dev/mapper/linear
# mount -o ro /dev/mapper/linear mnt
# md5sum image.img /dev/loop28 /dev/mapper/linear
56f56801923108d241947024926fea53 image.img
56f56801923108d241947024926fea53 /dev/loop28
d804867eab0106f9659c02a6add2f5da /dev/mapper/linear
It is my understanding that while mounting (even -o ro) might modify the
block device, a R/O block device should never be modifiable my anything.
This does not seem to be the case?
Best regards,
Johannes
--
"A PC without Windows is like a chocolate cake without mustard."
