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

[Luis Henriques <lhenriques@suse.de>]

David Disseldorp <ddiss@suse.de> writes:

> 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.

Yeah, also we must decode the attributes as hex otherwise we'll miss
non-string values.  Anyway, I'll see if I find something better.  Thanks,
David.

Cheers,
-- 
Luis