On Mon, 7 Nov 2011 04:42:54 +0100 Kay Sievers <kay.sievers@xxxxxxxx> wrote: > On Mon, Nov 7, 2011 at 03:52, NeilBrown <neilb@xxxxxxx> wrote: > > > However there is an important piece missing. When you remount,ro a > > filesystem, the block device doesn't get told so it thinks it is still open > > read/write. So md cannot tell mdmon that the array is now read-only > > That ro/rw flag is visible in /proc/self/mountinfo, shouldn't it be > possible for mdmon to poll() that file and let the kernel wake stuff > up when the ro/rw flag changes, like we do for the usual mount changes > already? > > Kay The ro/rw flag for file systems is in /proc/self/mountinfo. However I want the ro/rw flag for the block device. A block device can be partitioned so it might have multiple filesystems on it. and it might have swap too. or a dm table or another md device or an open file descriptor or .... Yes, I could maybe parse various different files and try to work out what is going on. But the kernel can easily *know* what is going on. Making this work "perfectly" would require md dropping its write-access to member devices when the last write-access to the top level device goes. And the same for dm and loop and ..... But just filesystems would go a long way to catching the common cases correctly. Thanks, NeilBrown
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