Re: [PATCH v2 1/2] generic/020: adjust max_attrval_size for ceph

[David Disseldorp <ddiss@suse.de>]

On Thu, 09 Jun 2022 15:54:15 +0100, Luís Henriques wrote:

> David Disseldorp <ddiss@suse.de> writes:
...
> > I take it a more exact calculation would be something like:
> > (64K - $max_attrval_namelen - sizeof(user.snrub="fish2\012"))?
> >
> > Perhaps you could calculate this on the fly for CephFS by passing in the
> > filename and subtracting the `getfattr -d $filename` results... That
> > said, it'd probably get a bit ugly, expecially if encoding needs to be
> > taken into account.  
> 
> In fact, this is *exactly* what I had before Dave suggested to keep it
> simple.

Arg, sorry I missed your previous round.

> After moving the code back into common/attr, where's how the
> generic code would look like:
> 
> +       ceph)
> +		# CephFS does have a limit for the whole set of names+values
> +		# attributes in a file.  Thus, it is necessary to get the sizes
> +		# of all names and values already existent and subtract them to
> +		# the (default) maximum, which is 64k.
> +		local len=0
> +		while read line; do
> +			# skip 1st line
> +			[ "$line" != "${line#'#'}" ] && continue
> +			n=$(echo $line | awk -F"=0x" '{print $1}')
> +			v=$(echo $line | awk -F"=0x" '{print $2}')
> +			nlen=${#n}
> +			vlen=${#v}
> +			# total is the sum of the name len and the value len
> +			# divided by 2 because we're dumping them in hex format
> +			t=$(($nlen + $vlen / 2))
> +			len=$(($len + $t))
> +		done <<< $(_getfattr -d -e hex $file 2> /dev/null)
> +		echo $((65536 - $max_attrval_namelen - $len))
> +		;;
> 
> so... yeah, I'm not particularly gifted on shell, it could probably be
> done in more clever/cleaner ways.  Anyway, I'm open to revisit this if
> this is the preferred solution.

hmm, I was hoping something like...
(( 65536 - $max_attrval_namelen - $(getfattr -d $file | _filter | wc -c) ))
would be possible, but getfattr output does make it a bit too messy.

Cheers, David