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From: David Sterba <dsterba@suse.cz>
To: dsterba@suse.cz, Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>,
	linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 4/6] btrfs: add wrapper for conditional start of exclusive operation
Date: Thu, 27 May 2021 00:24:38 +0200	[thread overview]
Message-ID: <20210526222438.GJ7604@twin.jikos.cz> (raw)
In-Reply-To: <20210521164551.GP7604@twin.jikos.cz>

On Fri, May 21, 2021 at 06:45:51PM +0200, David Sterba wrote:
> On Fri, May 21, 2021 at 09:29:16AM -0400, Josef Bacik wrote:
> > On 5/21/21 8:06 AM, David Sterba wrote:
> > > +		/*
> > > +		 * This blocks any exclop finish from setting it to NONE, so we
> > > +		 * request cancelation. Either it runs and we will wait for it,
> > > +		 * or it has finished and no waiting will happen.
> > > +		 */
> > > +		atomic_inc(&fs_info->reloc_cancel_req);
> > > +		btrfs_exclop_start_unlock(fs_info);
> > > +
> > > +		if (test_bit(BTRFS_FS_RELOC_RUNNING, &fs_info->flags))
> > > +			wait_on_bit(&fs_info->flags, BTRFS_FS_RELOC_RUNNING,
> > > +				    TASK_INTERRUPTIBLE);
> > 
> > Do we want to capture the return value here, in case the user hit's ctrl+c we 
> > can return -EINTR instead so we don't think it succeeded?  Thanks,
> 
> The cancel request will stay, so only the waiting part won't happen. I'm
> not sure if this is worth to distinguish the two states, eg. allow progs
> to print a different message.

So as the cancelling would happen I hope it's ok to return the ECANCELED
error in all cases. Other operations like balance or scrub aren't
interruptible and wait until the condition is satisified, but there's a
different pattern regarding the cancel request so it has to be that way
there. This could be unified but right now I don't see the need for
that.

> Maybe a waiting and non-waiting cancel modes would be also useful. As
> the interface is string-based we can also add 'status' that would say if
> it's running or not. This should cover the usecases, but would be
> a bit more complicated in the state transitions.

I've asked on IRC what's the expected behaviour of cancel command
regarding waiting/not waiting. Seems that 'wait until it's finished' is
preferred and it's consistent with what scrub and balance (cancel) do.

  reply	other threads:[~2021-05-26 22:27 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-21 12:06 [PATCH 0/6] Support resize and device delete cancel ops David Sterba
2021-05-21 12:06 ` [PATCH 1/6] btrfs: protect exclusive_operation by super_lock David Sterba
2021-05-21 13:37   ` Josef Bacik
2021-05-21 12:06 ` [PATCH 2/6] btrfs: add cancelable chunk relocation support David Sterba
2021-05-21 13:21   ` Josef Bacik
2021-05-26 22:56     ` David Sterba
2021-06-16 13:54   ` Filipe Manana
2021-06-16 13:55     ` Filipe Manana
2021-06-16 15:53       ` David Sterba
2021-06-16 15:58       ` [PATCH v2] btrfs: add cancellable " David Sterba
2021-06-17  9:18         ` Filipe Manana
2021-05-21 12:06 ` [PATCH 3/6] btrfs: introduce try-lock semantics for exclusive op start David Sterba
2021-05-21 13:38   ` Josef Bacik
2021-05-27  7:43   ` Anand Jain
2021-05-28 12:30     ` David Sterba
2021-05-29 13:48       ` Anand Jain
2021-05-31 18:23         ` David Sterba
2021-05-21 12:06 ` [PATCH 4/6] btrfs: add wrapper for conditional start of exclusive operation David Sterba
2021-05-21 13:29   ` Josef Bacik
2021-05-21 16:45     ` David Sterba
2021-05-26 22:24       ` David Sterba [this message]
2021-05-21 12:06 ` [PATCH 5/6] btrfs: add cancelation to resize David Sterba
2021-05-21 13:38   ` Josef Bacik
2021-05-21 12:06 ` [PATCH 6/6] btrfs: add device delete cancel David Sterba
2021-05-21 13:38   ` Josef Bacik
2021-05-21 12:06 ` [PATCH 1/2] btrfs-progs: device remove: add support for cancel David Sterba
2021-05-21 12:06 ` [PATCH 2/2] btrfs-progs: fi resize: " David Sterba
2021-12-14 14:49 ` [PATCH 0/6] Support resize and device delete cancel ops Anand Jain
2021-12-15 15:13   ` David Sterba

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