Date: Fri, 17 Jul 2015 16:22:51 +0200
From: Pali =?utf-8?B?Um9ow6Fy?= <pali.rohar@gmail.com>
To: Mike Snitzer <snitzer@redhat.com>
Cc: Alasdair Kergon <agk@redhat.com>, Neil Brown <neilb@suse.de>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
        linux-raid@vger.kernel.org, dm-devel@redhat.com,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v2 2/3] dm: Export function dm_suspend_md()
Message-ID: <20150717142251.GA12011@pali>
References: <1428254419-7334-1-git-send-email-pali.rohar@gmail.com>
 <1434885634-19895-1-git-send-email-pali.rohar@gmail.com>
 <1434885634-19895-3-git-send-email-pali.rohar@gmail.com>
 <20150717140438.GA29704@redhat.com>
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On Friday 17 July 2015 10:04:39 Mike Snitzer wrote:
> On Sun, Jun 21 2015 at  7:20am -0400,
> Pali Rohár <pali.rohar@gmail.com> wrote:
> 
> > This patch exports function dm_suspend_md() which suspend mapped device so other
> > kernel drivers can use it and could suspend mapped device when needed.
> > 
> > Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
> > ---
> >  drivers/md/dm.c |    6 ++++++
> >  drivers/md/dm.h |    5 +++++
> >  2 files changed, 11 insertions(+)
> > 
> > diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> > index 2caf492..03298ff 100644
> > --- a/drivers/md/dm.c
> > +++ b/drivers/md/dm.c
> > @@ -3343,6 +3343,12 @@ out:
> >  	return r;
> >  }
> >  
> > +int dm_suspend_md(struct mapped_device *md)
> > +{
> > +	return dm_suspend(md, DM_SUSPEND_LOCKFS_FLAG);
> > +}
> > +EXPORT_SYMBOL_GPL(dm_suspend_md);
> > +
> >  /*
> >   * Internal suspend/resume works like userspace-driven suspend. It waits
> >   * until all bios finish and prevents issuing new bios to the target drivers.
> 
> To do this properly you should be introducing a variant of
> dm_internal_suspend.  We currently have two variants:
> dm_internal_suspend_fast
> dm_internal_suspend_noflush
> 
> The reason to use a dm_internal_suspend variant is this suspend was
> _not_ initiated by an upper level ioctl (from userspace).  It was
> done internally from within the target.
> 
> You're explicitly using DM_SUSPEND_LOCKFS_FLAG above.. meaning you're
> interested in flushing all pending IO (in the FS layered on dm-crupt, if
> one exists).
> 
> But see the comment in __dm_internal_suspend() about TASK_UNINTERRUPTIBLE.
> If you're OK with the dm-crypt initiated suspend being
> TASK_UNINTERRUPTIBLE then you could just introduce:
> 
> void dm_internal_suspend_uninterruptible_flush(struct mapped_device *md)
> {
>         mutex_lock(&md->suspend_lock);
>         __dm_internal_suspend(md, DM_SUSPEND_LOCKFS_FLAG);
>         mutex_unlock(&md->suspend_lock);
> }
> EXPORT_SYMBOL_GPL(dm_internal_suspend_uninterruptible_flush);
> 
> Otherwise, there is much more extensive DM core changes needed to
> __dm_internal_suspend() and .presuspend to properly support
> TASK_INTERRUPTIBLE.

Hi! I will look at dm_internal_suspend. Anyway use case for suspend is
from dm-crypt to do both operations: suspend + key wipe. It means that
without entering key again from userspace, resume is not possible. So my
question is: It is possible to do internal suspend and then using resume
from userspace via ioctl?

-- 
Pali Rohár
pali.rohar@gmail.com
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