Re: [PATCH] xfs_db: properly set inode type

Dave Chinner
2017-07-18T02:20:28Z

On Mon, Jul 17, 2017 at 03:51:50PM -0500, Eric Sandeen wrote:
>
>
> On 06/28/2017 11:01 PM, Eric Sandeen wrote:
> >> I guess there's also the problem that if inodesize != 512 then what are
> >> we targeting, anyway? If inodesize = 256 then we can only hit
> >> even-numbered inodes (not so bad) but if inodesize > 512 then do we jump
> >> back to wherever the inode starts? Or just give the user what they
> >> asked for, even if it's garbage?
> > Oh, hum. Right, big inodes....
> >
> > So I'm trying to go from disk location to inode number, but the current
> > disk location may not even be the start of an inode. Hell. Well, I'm
> > sure I could craft a test to disallow "type inode" if the current location
> > cannot be on an inode boundary. But is that too clever? Should the
> > debug tool just do what the user asks?
> >
> >> (FWIW I was fine with xfs_db being dumb and giving you exactly what you
> >> point it at, even if that makes no sense. :P)
> > yeah, if you do "daddr 0" "type agf" it'll squawk, too, so it's fine to
> > do the dumb user's bidding...
>
> So as I have it today, issuing "type inode" will actually re-align you
> to an inode offset even if you're not on one:
>
> xfs_db> sb 0
> xfs_db> addr rootino
> xfs_db> daddr
> current daddr is 128
> xfs_db> daddr 129
> xfs_db> type inode
> xfs_db> daddr
> current daddr is 128
> xfs_db>
>
> good? bad? indifferent? I'm thinking "bad" but we have no mechanism to
> read a batch of inodes in xfs_db other than by passing in a legit inode number.
>
> And we have no mechanism to read only a /single/ inode...
>
> Maybe print a warning about the re-alignment and carry on?

xfs_db is meant to be a developer tool, not idiot-proof. :P

i.e. some knowledge of the layout of the metadata you are trying
to examine is expected. I would not like xfs_db to change the daddr
I've specified simply because I tried to parse it as the wrong
object type....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com