Re: [PATCH] btrfs: Add more details while checking tree block

[Hugo Mills <hugo@carfax.org.uk>]

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On Fri, Jun 22, 2018 at 05:26:02PM +0200, Hans van Kranenburg wrote:
> On 06/22/2018 01:48 PM, Nikolay Borisov wrote:
> > 
> > 
> > On 22.06.2018 04:52, Su Yue wrote:
> >> For easier debug, print eb->start if level is invalid.
> >> Also make print clear if bytenr found is not expected.
> >>
> >> Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com>
> >> ---
> >>  fs/btrfs/disk-io.c | 8 ++++----
> >>  1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> >> index c3504b4d281b..a90dab84f41b 100644
> >> --- a/fs/btrfs/disk-io.c
> >> +++ b/fs/btrfs/disk-io.c
> >> @@ -615,8 +615,8 @@ static int btree_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
> >>  
> >>  	found_start = btrfs_header_bytenr(eb);
> >>  	if (found_start != eb->start) {
> >> -		btrfs_err_rl(fs_info, "bad tree block start %llu %llu",
> >> -			     found_start, eb->start);
> >> +		btrfs_err_rl(fs_info, "bad tree block start want %llu have %llu",
> > 
> > nit: I'd rather have the want/have in brackets (want %llu have% llu)
> 
> From a user support point of view, this text should really be improved.
> There are a few places where 'want' and 'have' are reported in error
> strings, and it's totally unclear what they mean.
> 
> Intuitively I'd say when checking a csum, the "want" would be what's on
> disk now, since you want that to be correct, and the "have" would be
> what you have calculated, but it's actually the other way round, or
> wasn't it? Or was it?
> 
> Every time someone pastes such a message when we help on IRC for
> example, there's confusion, and I have to look up the source again,
> because I always forget.
> 
> What about (%llu stored on disk, %llu calculated now) or something similar?

   Yes, definitely this. I experience the same confusion as Hans, and
I think a lot of other people do, too. I usually read "want" and
"have" the wrong way round, so more clarity would be really helpful.

   Hugo.

> >> +			     eb->start, found_start);
> >>  		ret = -EIO;
> >>  		goto err;
> >>  	}
> >> @@ -628,8 +628,8 @@ static int btree_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
> >>  	}
> >>  	found_level = btrfs_header_level(eb);
> >>  	if (found_level >= BTRFS_MAX_LEVEL) {
> >> -		btrfs_err(fs_info, "bad tree block level %d",
> >> -			  (int)btrfs_header_level(eb));
> >> +		btrfs_err(fs_info, "bad tree block level %d on %llu",
> >> +			  (int)btrfs_header_level(eb), eb->start);
> >>  		ret = -EIO;
> >>  		goto err;
> >>  	}
> >>
> 

-- 
Hugo Mills             | "There's a Martian war machine outside -- they want
hugo@... carfax.org.uk | to talk to you about a cure for the common cold."
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                           Stephen Franklin, Babylon 5

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