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SubjectRe: [PATCH v2 2/7] erofs: some marcos are much more readable as a function
Hi Christoph,

On Fri, Aug 30, 2019 at 08:45:51AM -0700, Christoph Hellwig wrote:
> On Thu, Aug 29, 2019 at 08:16:27PM -0700, Joe Perches wrote:
> > > - sizeof(__u32) * ((__count) - 1); })
> > > +static inline unsigned int erofs_xattr_ibody_size(__le16 d_icount)
> > > +{
> > > + unsigned int icount = le16_to_cpu(d_icount);
> > > +
> > > + if (!icount)
> > > + return 0;
> > > +
> > > + return sizeof(struct erofs_xattr_ibody_header) +
> > > + sizeof(__u32) * (icount - 1);
> >
> > Maybe use struct_size()?
>
> Declaring a variable that is only used for struct_size is rather ugly.
> But while we are nitpicking: you don't need to byteswap to check for 0,
> so the local variable could be avoided.
>
> Also what is that magic -1 for? Normally we use that for the
> deprecated style where a variable size array is declared using
> varname[1], but that doesn't seem to be the case for erofs.

I have to explain more about this (sorry about my awkward English)
here i_xattr_icount is to represent the size of xattr field of erofs, as follows:
0 - no xattr at all (no erofs_xattr_ibody_header)
_______
| inode |
|_______|

1 - a erofs_xattr_ibody_header (12 byte) + 4-byte (shared + inline) xattrs
2 - a erofs_xattr_ibody_header (12 byte) + 8-byte (shared + inline) xattrs
....
(that is the magic -1 means...)

In order to keep the number continuously, actually the content could be
an array of shared_xattr_id and
an inline xattr combination (struct erofs_xattr_entry + name + value)

Thanks,
Gao Xiang

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