Some block devices, such as LUKS-encrypted volumes mounted via
blkmap_crypt, only support read access. When ext4l attempts to write
the superblock during mount, the write fails and causes mount to fail.
Add a way to detect this read-only device detection:
- Test writes during mount by writing back the superblock data; if the
write fails, mark the device as read-only
- Update bdev_read_only() to return the actual read_only status
- Update sb_rdonly() to check the SB_RDONLY flag
This allows ext4l to successfully mount read-only devices like LUKS
volumes for read access.
We could perhaps have a read-only flag in the block device, but that is
left for another day.
Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
5161a55207