On Monday August 27, viro@xxxxxxxxxxxxxxxx wrote: > * a bug (AFAICT) in md.c - we open raid components r/w and if it > fails, it fails. Good for our purposes, but... how about raid0 on read-only > devices? In any case, we have a ready place to store mode_t, so it's not a > problem for getting the right value to blkdev_put(). FWIW, I think that > allowing fallback to r/o (and making the entire array r/o, of course) would > be a good thing to have. Any comments from drivers/md folks? I've never heard any suggestion of anybody wanting to include a readonly device in an md array - I guess one could imagine an array of CDROMs, but I doubt anyone would actually create one. However I agree that falling back to read-only (particular if the error value indicated that this was the only problem) would be a sensible thing to do in some circumstances. More interestingly: one could argue that when the md array is switched to read-only, each component device should be reopened as read-only. So I would really like the interface to have a way to switch a device between read-only and read-write without closing and re-opening. Though I guess opening and then closing as you suggest below would be OK. > * open_bdev_excl()/close_bdev_excl(). Needs an extra argument for > the latter. Two interesting callers: > * kill_block_super() - need to store relevant mode_t in superblock, > along with reference to bdev. Note that just looking at sb->s_flags is *not* > enough - some filesystems go read-only on errors and that changes ->s_flags. > Another side of that is explicit remount from r/o to r/w and there we have > a bug - we do _not_ tell the driver that something had happened. Proper > fix is simple enough - bdget() + blkdev_get() for write + blkdev_put() with > old mode_t (i.e. FMODE_READ) once we are done remounting (and similar for > explicit remount to r/o). I would *really* like to see this. When the root filesystem gets mounted read-only, I want md to know so that it can mark the array as 'clean' straight away. I really don't like having a reboot-notifier to mark all arrays as 'clean' on shutdown. So each device would be responsible for keeping a count of 'readonly' and 'read-write' accesses? Or would that be in common code? I look forward to this all getting cleaned up! NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
