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Re: any way to work backwards from xfs_inode_t to a filename?

To: Chris Friesen <chris.friesen@xxxxxxxxxxx>
Subject: Re: any way to work backwards from xfs_inode_t to a filename?
From: Ben Myers <bpm@xxxxxxx>
Date: Wed, 15 May 2013 17:10:00 -0500
Cc: Alex Elder <elder@xxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <5194050B.7010401@xxxxxxxxxxx>
References: <5194050B.7010401@xxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
Hey Chris,

On Wed, May 15, 2013 at 03:58:35PM -0600, Chris Friesen wrote:
> As I mentioned before I'm digging into some intermittent xfs
> corruption issues on an embedded system running a 2.6.27-based
> kernel.
> 
> In one case I've hit XFS_WANT_CORRUPTED_GOTO in
> xfs_free_ag_extent(). In this particular case the call chain was
> 
> xfs_free_ag_extent+0x55d/0x6e0
> xfs_free_extent+0xac/0xd0
> xfs_bmap_finish+0x156/0x1a0
> xfs_itruncate_finish+0x137/0x340
> xfs_inactive+0x386/0x4b0
> xfs_fs_clear_inode+0xc6/0x120
> clear_inode+0x58/0x110
> generic_delete_inode+0xff/0x110
> generic_drop_inode+0x16d/0x190
> iput+0x5d/0x70
> do_unlinkat+0x147/0x280
> sys_unlinkat+0x1d/0x40
> 
> I have two questions:
> 
> 1) do_unlinkat() has the filesystem path, but iput() returns void.
> Is there any way for me to add instrumentation to xfs_inactive() to
> work backwards from the xfs_inode_t pointer to print out a path to
> the file being deleted?

Use VFS_I to get to a 'struct inode' and from there you can look at the
dentries on i_dentry list and traverse back through the path by looking at
d_parent.  Might be easier to just print the path in do_unlinkat?

> 2) If this sort of corruption happens again, what's my best bet for
> figuring out the source of the problem?  This is an embedded system,
> so I need to be able to automate any data gathering (after which
> we'll run xfs_repair so we can return to service--any manual
> analysis will need to happen later based on stored data).

Can you grab a metadump before you repair the filesystem?

Thanks,
        Ben

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