Re: [PATCH blktests v2 3/4] Introduce the function _configure_null_blk()

[Omar Sandoval <osandov@osandov.com>]

On Sun, Mar 15, 2020 at 03:13:19PM -0700, Bart Van Assche wrote:
> Introduce a function for creating a null_blk device instance through
> configfs.
> 
> Suggested-by: Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  common/multipath-over-rdma | 17 +++++------------
>  common/null_blk            | 14 ++++++++++++++
>  tests/block/029            | 16 ++--------------
>  3 files changed, 21 insertions(+), 26 deletions(-)
> 
> diff --git a/common/multipath-over-rdma b/common/multipath-over-rdma
> index a56e7a8269db..7e610a0ccbbb 100644
> --- a/common/multipath-over-rdma
> +++ b/common/multipath-over-rdma
> @@ -620,18 +620,11 @@ run_fio() {
>  configure_null_blk() {
>  	local i
>  
> -	(
> -		cd /sys/kernel/config/nullb || return $?
> -		for i in nullb0 nullb1; do (
> -			{ mkdir -p $i &&
> -				  cd $i &&
> -				  echo 0 > completion_nsec &&
> -				  echo 512 > blocksize &&
> -				  echo $((ramdisk_size>>20)) > size &&
> -				  echo 1 > memory_backed &&
> -				  echo 1 > power; } || exit $?
> -		) done
> -	)
> +	for i in nullb0 nullb1; do
> +		_configure_null_blk nullb$i completion_nsec=0 blocksize=512 \
> +				    size=$((ramdisk_size>>20)) memory_backed=1 \
> +				    power=1 || return $?
> +	done
>  	ls -l /dev/nullb* &>>"$FULL"
>  }
>  
> diff --git a/common/null_blk b/common/null_blk
> index 6a5f99aaae9d..3c31db1ed4ac 100644
> --- a/common/null_blk
> +++ b/common/null_blk
> @@ -28,6 +28,20 @@ _init_null_blk() {
>  	return 0
>  }
>  
> +# Configure one null_blk instance with name $1 and parameters $2..${$#}.
> +_configure_null_blk() {
> +	local nullb=/sys/kernel/config/nullb/$1 param val
> +
> +	shift
> +	mkdir "$nullb" &&

Just make this mkdir "$nullb" || return $?

> +		while [ -n "$1" ]; do

The intention is clearer with while [[ $# > 0 ]]

> +			param="${1//=*}"
> +			val="${1#${param}=}"

These are all arcane bash incantations, but the following seem slighly
clearer to me:

param="${1%%=*}"
val="${1#*=}"

I.e., for param we remove the equal sign and everything after it, and
for val we remove everything up to the equal sign.

> +			shift
> +			echo "$val" > "$nullb/$param" || return $?
> +		done
> +}
> +