Re: [PATCH] btrfs: Remove WARN_ON for unaligned device created before v4.13 and adds more user friendly output

[Satoru Takeuchi <satoru.takeuchi@gmail.com>]

At Sat, 23 Sep 2017 10:19:26 +0900,
Satoru Takeuchi wrote:
> 
> At Wed, 20 Sep 2017 15:18:43 +0900,
> Qu Wenruo wrote:
> > 
> > Commit 7dfb8be11b5d ("btrfs: Round down values which are written for
> > total_bytes_size") is fixing the unaligned device size caused by
> > adding/shrinking device.
> > 
> > It added a new WARN_ON() when device size is unaligned.
> > This is fine for new device added to btrfs using v4.13 kernel, but not
> > existing device whose total_bytes is already unaligned.
> > 
> > And the WARN_ON() will get triggered every time a block group get
> > created/removed on the unaligned device.
> > 
> > This patch will remove the WARN_ON(), and warn user more gently what's
> > happening and how to fix it.
> > 
> > Reported-by: Rich Rauenzahn <rich@shroop.net>
> > Fixes: 7dfb8be11b5d ("btrfs: Round down values which are written for
> > total_bytes_size")
> > Signed-off-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
> > ---
> >  fs/btrfs/ctree.h   |  1 -
> >  fs/btrfs/volumes.c | 16 ++++++++++++----
> >  2 files changed, 12 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> > index 5a8933da39a7..4de9269e435a 100644
> > --- a/fs/btrfs/ctree.h
> > +++ b/fs/btrfs/ctree.h
> > @@ -1562,7 +1562,6 @@ static inline void btrfs_set_device_total_bytes(struct extent_buffer *eb,
> >  {
> >  	BUILD_BUG_ON(sizeof(u64) !=
> >  		     sizeof(((struct btrfs_dev_item *)0))->total_bytes);
> > -	WARN_ON(!IS_ALIGNED(val, eb->fs_info->sectorsize));
> >  	btrfs_set_64(eb, s, offsetof(struct btrfs_dev_item, total_bytes), val);
> >  }
> >  
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> > index 0e8f16c305df..afae25df6a8c 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -6472,15 +6472,23 @@ static int read_one_chunk(struct btrfs_fs_info *fs_info, struct btrfs_key *key,
> >  	return 0;
> >  }
> >  
> > -static void fill_device_from_item(struct extent_buffer *leaf,
> > -				 struct btrfs_dev_item *dev_item,
> > -				 struct btrfs_device *device)
> > +static void fill_device_from_item(struct btrfs_fs_info *fs_info,
> > +				  struct extent_buffer *leaf,
> > +				  struct btrfs_dev_item *dev_item,
> > +				  struct btrfs_device *device)
> >  {
> >  	unsigned long ptr;
> >  
> >  	device->devid = btrfs_device_id(leaf, dev_item);
> >  	device->disk_total_bytes = btrfs_device_total_bytes(leaf, dev_item);
> >  	device->total_bytes = device->disk_total_bytes;
> > +	if (!IS_ALIGNED(device->total_bytes, fs_info->sectorsize)) {
> > +		btrfs_warn(fs_info,
> > +			   "devid %llu has unaligned total bytes %llu",
> > +			   device->devid, device->disk_total_bytes);
> > +		btrfs_warn(fs_info,
> > +			   "please shrink the device a little and resize back to fix it");
> > +	}
> 
> How about telling uses to know device->total_bytes should be alligned
> to fs_info->sectorsize here?
> 
> Thanks,

I should make my comment clearer, sorry.

===
+	if (!IS_ALIGNED(device->total_bytes, fs_info->sectorsize)) {
+		btrfs_warn(fs_info,
+			   "devid %llu: total bytes %llu should be aligned to %u bytes",
+			   device->devid, device->disk_total_bytes, fs_info->sectorsize);
+		btrfs_warn(fs_info,
+			   "please shrink the device a little and resize back to fix it");
+	}
===

Thanks,
Satoru

> Satoru
> 
> >  	device->commit_total_bytes = device->disk_total_bytes;
> >  	device->bytes_used = btrfs_device_bytes_used(leaf, dev_item);
> >  	device->commit_bytes_used = device->bytes_used;
> > @@ -6625,7 +6633,7 @@ static int read_one_dev(struct btrfs_fs_info *fs_info,
> >  			return -EINVAL;
> >  	}
> >  
> > -	fill_device_from_item(leaf, dev_item, device);
> > +	fill_device_from_item(fs_info, leaf, dev_item, device);
> >  	device->in_fs_metadata = 1;
> >  	if (device->writeable && !device->is_tgtdev_for_dev_replace) {
> >  		device->fs_devices->total_rw_bytes += device->total_bytes;
> > -- 
> > 2.14.1
> > 
> > --
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