[PATCH] md: allow md arrays to be started read-only (module parameter).
When an md array is started, the superblock will be written, and resync may commense. This is not good if you want to be completely read-only as, for example, when preparing to resume from a suspend-to-disk image. So introduce a module parameter "start_ro" which can be set to '1' at boot, at module load, or via /sys/module/md_mod/parameters/start_ro When this is set, new arrays get an 'auto-ro' mode, which disables all internal io (superblock updates, resync, recovery) and is automatically switched to 'rw' when the first write request arrives. The array can be set to true 'ro' mode using 'mdadm -r' before the first write request, or resync can be started without a write using 'mdadm -w'. Signed-off-by: Neil Brown <neilb@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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