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

[David Disseldorp <ddiss@suse.de>]

Hi Luís,

On Thu,  9 Jun 2022 11:53:42 +0100, Luís Henriques wrote:

> CephFS doesn't have a maximum xattr size.  Instead, it imposes a maximum
> size for the full set of xattrs names+values, which by default is 64K.
> 
> This patch fixes the max_attrval_size so that it is slightly < 64K in
> order to accommodate any already existing xattrs in the file.
> 
> Signed-off-by: Luís Henriques <lhenriques@suse.de>
> ---
>  tests/generic/020 | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/generic/020 b/tests/generic/020
> index d8648e96286e..76f13220fe85 100755
> --- a/tests/generic/020
> +++ b/tests/generic/020
> @@ -128,7 +128,7 @@ _attr_get_max()
>  	pvfs2)
>  		max_attrval_size=8192
>  		;;
> -	xfs|udf|9p|ceph)
> +	xfs|udf|9p)
>  		max_attrval_size=65536
>  		;;
>  	bcachefs)
> @@ -139,6 +139,14 @@ _attr_get_max()
>  		# the underlying filesystem, so just use the lowest value above.
>  		max_attrval_size=1024
>  		;;
> +	ceph)
> +		# CephFS does not have a maximum value for attributes.  Instead,
> +		# it imposes a maximum size for the full set of xattrs
> +		# names+values, which by default is 64K.  Set this to a value
> +		# that is slightly smaller than 64K so that it can accommodate
> +		# already existing xattrs.
> +		max_attrval_size=65000
> +		;;

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.

Reviewed-by: David Disseldorp <ddiss@suse.de>

Cheers, David