On 4/9/2012 7:43 PM, NeilBrown wrote:
It will reject writes from user-space, and it will reject attempts to mount a filesystem unless the filesystem is mounted "read-only". But if a read-only mounted filesystem decides to write anyway (XFS, ext3, ext4...) then the block layer doesn't stop it.
How does that work? How does the block layer know or care what mount flags are used? My understanding is that setting the block layer read-only flag with blockdev --setro actually causes the write bios to be rejected, thus preventing ext[34] from playing back the journal. Ubuntu has been using this to prevent accidental damage by read-only mounts since this abhorrent behavior was discovered. I would think that md should work the same way.
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