Re: [PATCH v3 7/7] btrfs: Enhance missing device kernel message

[Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>]

At 03/08/2017 01:26 PM, Andrei Borzenkov wrote:
> 08.03.2017 05:41, Qu Wenruo пишет:
> > For missing device, btrfs will just refuse to mount with almost
> > meaningless kernel message like:
> >
> >  BTRFS info (device vdb6): disk space caching is enabled
> >  BTRFS info (device vdb6): has skinny extents
> >  BTRFS error (device vdb6): failed to read the system array: -5
> >  BTRFS error (device vdb6): open_ctree failed
> >
> > This patch will add extra device missing output, making the result to:
> >
> >  BTRFS info (device vdb6): disk space caching is enabled
> >  BTRFS info (device vdb6): has skinny extents
> >  BTRFS warning (device vdb6): devid 2 uuid 80470722-cad2-4b90-b7c3-fee294552f1b is missing
> >  BTRFS error (device vdb6): failed to read the system array: -5
>
> Unfortunately it is still unclear that failure to mount is caused by
> missing device. As you explained (and the whole reason of this patch
> series) we still are able to mount even with missing device(s). It
> should print error (not warning) telling that some extents are not
> accessible due to missing device(s)

If you specify -o degraded to allow read_chunk_tree to progress further, 
then there will be detailed reason for it:

 BTRFS info (device vdb7): allowing degraded mounts
 BTRFS info (device vdb7): disk space caching is enabled
 BTRFS info (device vdb7): has skinny extents
 BTRFS info (device vdb7): flagging fs with big metadata feature
 BTRFS warning (device vdb7): devid 1 uuid 
21cdf493-9d75-4a78-a8ee-d7426521a9f1 is missing
 BTRFS warning (device vdb7): chunk 12582912 missing 1 devices, max 
tolerance is 0 for writeble mount
 BTRFS warning (device vdb7): writeable mount is not allowed due to too 
many missing devices
 BTRFS error (device vdb7): open_ctree failed

Otherwise, normal mount doesn't allow any missing device and will just 
return -EIO from btrfs_read_chunk_tree(), preventing us from going to 
btrfs_check_rw_degradable().

I'll add more output for detailed reason why the mount fails in another 
patchset.

Thanks,
Qu

> >  BTRFS error (device vdb6): open_ctree failed
> >
> > Signed-off-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
> > Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx>
> > ---
> >  fs/btrfs/volumes.c | 24 +++++++++++++++++-------
> >  fs/btrfs/volumes.h |  2 ++
> >  2 files changed, 19 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> > index 765d213ac5ef..f2c878d5f714 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -6442,6 +6442,7 @@ static int read_one_chunk(struct btrfs_fs_info *fs_info, struct btrfs_key *key,
> >  		if (!map->stripes[i].dev &&
> >  		    !btrfs_test_opt(fs_info, DEGRADED)) {
> >  			free_extent_map(em);
> > +			btrfs_report_missing_device(fs_info, devid, uuid);
> >  			return -EIO;
> >  		}
> >  		if (!map->stripes[i].dev) {
> > @@ -6452,8 +6453,7 @@ static int read_one_chunk(struct btrfs_fs_info *fs_info, struct btrfs_key *key,
> >  				free_extent_map(em);
> >  				return -EIO;
> >  			}
> > -			btrfs_warn(fs_info, "devid %llu uuid %pU is missing",
> > -				   devid, uuid);
> > +			btrfs_report_missing_device(fs_info, devid, uuid);
> >  		}
> >  		map->stripes[i].dev->in_fs_metadata = 1;
> >  	}
> > @@ -6570,17 +6570,21 @@ static int read_one_dev(struct btrfs_fs_info *fs_info,
> >
> >  	device = btrfs_find_device(fs_info, devid, dev_uuid, fs_uuid);
> >  	if (!device) {
> > -		if (!btrfs_test_opt(fs_info, DEGRADED))
> > +		if (!btrfs_test_opt(fs_info, DEGRADED)) {
> > +			btrfs_report_missing_device(fs_info, devid, dev_uuid);
> >  			return -EIO;
> > +		}
> >
> >  		device = add_missing_dev(fs_devices, devid, dev_uuid);
> >  		if (!device)
> >  			return -ENOMEM;
> > -		btrfs_warn(fs_info, "devid %llu uuid %pU missing",
> > -				devid, dev_uuid);
> > +		btrfs_report_missing_device(fs_info, devid, dev_uuid);
> >  	} else {
> > -		if (!device->bdev && !btrfs_test_opt(fs_info, DEGRADED))
> > -			return -EIO;
> > +		if (!device->bdev) {
> > +			btrfs_report_missing_device(fs_info, devid, dev_uuid);
> > +			if (!btrfs_test_opt(fs_info, DEGRADED))
> > +				return -EIO;
> > +		}
> >
> >  		if(!device->bdev && !device->missing) {
> >  			/*
> > @@ -6806,6 +6810,12 @@ static bool device_has_rw_degrade_error(struct extra_rw_degrade_errors *errors,
> >  	return ret;
> >  }
> >
> > +void btrfs_report_missing_device(struct btrfs_fs_info *fs_info, u64 devid,
> > +				 u8 *uuid)
> > +{
> > +	btrfs_warn_rl(fs_info, "devid %llu uuid %pU is missing", devid, uuid);
> > +}
> > +
> >  /*
> >   * Check if all chunks in the fs is OK for read-write degraded mount
> >   *
> > diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> > index 67d7474e42a3..1f6ab55640da 100644
> > --- a/fs/btrfs/volumes.h
> > +++ b/fs/btrfs/volumes.h
> > @@ -573,4 +573,6 @@ void record_extra_rw_degrade_error(struct extra_rw_degrade_errors *errors,
> >
> >  bool btrfs_check_rw_degradable(struct btrfs_fs_info *fs_info,
> >  			       struct extra_rw_degrade_errors *errors);
> > +void btrfs_report_missing_device(struct btrfs_fs_info *fs_info, u64 devid,
> > +				 u8 *uuid);
> >  #endif


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