Re: [PATCH 29/32] mkfs: support RT data checksums

[Christoph Hellwig <hch@lst.de>]

On Fri, Sep 25, 2026 at 04:39:08PM -0700, Darrick J. Wong wrote:
> >  	R_RESERVED,
> > +	R_CSUM,
> > +	R_CSUMBSIZE,
> 
> BTW now that Andrey has merged the config file generator code, you'll
> have to add the relevant R_CSUM/R_CSUMBSIZE bits to libfrog/fsgeom.c.

Oh, right.  Another fun learning experience :)

> >  /* data subvol */	[-d agcount=n,agsize=n,file,name=xxx,size=num,\n\
> >  			    (sunit=value,swidth=value|su=num,sw=num|noalign),\n\
> > -			    sectsize=num,concurrency=num]\n\
> > +			    sectsize=num,concurrency=num,\n\
> > +			    csum=type]\n\
> 
> There's no csum= parameter for -d, or at least I didn't see a D_CSUM
> entry above.

Correct.  This is left from an earlier series where I tried to support
cheksums on the data device using NVMe non-PI metadata, but that didn't
got to well.

> > +	cfg->sb_feat.rtcsum_blklog = 0;
> > +	for (l = cfg->rtcsumbsize; l > 1; l >>= 1)
> > +		cfg->sb_feat.rtcsum_blklog++;
> 
> log2_roundup?

Ah, nice.  I was looking for a userspace version of the kernels ilog2,
but could not find it.