Re: [PATCH 1/6] xfs: remove the agfl_bno member from struct xfs_agfl

[Christoph Hellwig <hch@lst.de>]

On Mon, Feb 03, 2020 at 11:46:11AM -0600, Eric Sandeen wrote:
> On 1/30/20 7:33 AM, Christoph Hellwig wrote:
> > struct xfs_agfl is a header in front of the AGFL entries that exists
> > for CRC enabled file systems.  For not CRC enabled file systems the AGFL
> > is simply a list of agbno.  Make the CRC case similar to that by just
> > using the list behind the new header.  This indirectly solves a problem
> > with modern gcc versions that warn about taking addresses of packed
> > structures (and we have to pack the AGFL given that gcc rounds up
> > structure sizes).  Also replace the helper macro to get from a buffer
> > with an inline function in xfs_alloc.h to make the code easier to
> > read.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> I like it.
> 
> Giving it an RVB but are we 100% sure that there won't ever be any padding
> after the xfs_agfl structure before the bno?  I don't understand gcc
> alignment magic.

That is at least the definition of __attribute__((packed))..