[systemd-devel] systemd kills mdmon if it was started manually by user

[NeilBrown]

On Mon, 7 Nov 2011 04:42:54 +0100 Kay Sievers <kay.sievers at vrfy.org> wrote:

> On Mon, Nov 7, 2011 at 03:52, NeilBrown <neilb at suse.de> 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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