linux-kernel - Re: [PATCH 2/6] f2fs: support goingdown for fs shutdown

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Date:	Fri, 9 Jan 2015 07:54:16 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Eric Sandeen <sandeen@...deen.net>
Cc:	Jaegeuk Kim <jaegeuk@...nel.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH 2/6] f2fs: support goingdown for fs shutdown

On Thu, Jan 08, 2015 at 02:33:17PM -0600, Eric Sandeen wrote:
> On 1/8/15 2:18 PM, Jaegeuk Kim wrote:
> > On Thu, Jan 08, 2015 at 01:54:20PM -0600, Eric Sandeen wrote:
> >> On 1/8/15 12:10 PM, Jaegeuk Kim wrote:
> >>> This patch add an ioctl to shutdown f2fs, which stops all the further block
> >>> writes after this point.
> >>
> >> would it make sense to just re-use the xfs ioctl nr, if the semantics are
> >> the same?
> > 
> > The semantics are not same for now.
> > In order to reuse xfs ioctl, it needs to support options for flushing logs.
> 
> the xfs iotl has 3 behaviors optional:
> 
> #define XFS_FSOP_GOING_FLAGS_DEFAULT            0x0     /* going down */
> #define XFS_FSOP_GOING_FLAGS_LOGFLUSH           0x1     /* flush log but not data */
> #define XFS_FSOP_GOING_FLAGS_NOLOGFLUSH         0x2     /* don't flush log nor data */
> 
> if f2fs currently supports a subset, you could just -EOPNOTSUPP on the others.

No, just do a default shutdown operation if the semantics cannot be
supported.

	- XFS_FSOP_GOING_FLAGS_DEFAULT ==
		consistent on disk before shutdown
			+ implemented by freeze/thaw/shutdown sequence
	- XFS_FSOP_GOING_FLAGS_LOGFLUSH ==
		consistent journal on disk before shutdown
			+ implemented by journal flush/shutdown sequence
	- XFS_FSOP_GOING_FLAGS_NOLOGFLUSH ==
		nothing consistent on disk before shutdown
			+ just a shutdown call.

f2fs can at least support XFS_FSOP_GOING_FLAGS_DEFAULT and
XFS_FSOP_GOING_FLAGS_NOLOGFLUSH....

> If the semantics are completely different, maybe it shouldn't share the
> name at all.  ;)

The semantics are quite clear and generic - when you look at what
they actually mean rather than looking at the implementation.
There's no need for new ioctls here.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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