Re: [PATCH 12/13] xfs: add version 3 inode format with CRCs

Christoph Hellwig
2009-02-12T18:52:31Z

On Thu, Feb 12, 2009 at 12:42:02PM -0600, Eric Sandeen wrote:
> Josef 'Jeff' Sipek wrote:
> > On Tue, Feb 10, 2009 at 03:22:53PM -0500, Christoph Hellwig wrote:
> > ...
> >> Index: xfs/fs/xfs/xfs_dinode.h
> >> ===================================================================
> >> --- xfs.orig/fs/xfs/xfs_dinode.h 2009-02-10 19:45:51.939069576 +0100
> >> +++ xfs/fs/xfs/xfs_dinode.h 2009-02-10 19:45:59.195068745 +0100
> >> @@ -69,11 +69,32 @@ typedef struct xfs_dinode {
> >>
> >> /* di_next_unlinked is the only non-core field in the old dinode */
> >> __be32 di_next_unlinked;/* agi unlinked list ptr */
> >> -} __attribute__((packed)) xfs_dinode_t;
> >> +
> >> + /* start of the extended dinode, writable fields */
> >> + __be32 di_crc; /* CRC of the inode */
> >> + __be64 di_changecount; /* number of attribute changes */
> >> + __u8 di_pad2[16]; /* more padding for future expansion */
> >> +
> >> + /* fields only written to during inode creation */
> >> + xfs_timestamp_t di_crtime; /* time created */
> >> + __be64 di_ino; /* inode number */
> >> + uuid_t di_uuid; /* UUID of the filesystem */
> >> +} xfs_dinode_t;
> >
> > Hrm...removing the packed attribute... Eric, do you remember the ARM ABI
> > alignment rules? Regardless of ARM, are those fields aligned nicely? (From a
> > quick glance at the code looks ok.)
>
> I'll just have to just test it again I suppose. Removing packed is
> good, as long as the padding makes it all come out right.

The reason why the current dinode needs the packed attribute is that
it's end on an un-even 32bit word, and thus the last field might be
wrongly aligned on 64-bit big-endian platforms (same issue as the
bad features2 one). With the CRC patchset we now have a dinode
that's properly aligned on a even 32bit word.

>
> -=Eric
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