Re: [PATCH v2 2/3] common/zoned: add _create_zloop

["Darrick J. Wong" <djwong@kernel.org>]

On Sun, Oct 12, 2025 at 09:36:18AM +0900, Damien Le Moal wrote:
> On 2025/10/11 18:34, Johannes Thumshirn wrote:
> > On 10/8/25 5:08 PM, Darrick J. Wong wrote:
> >> On Wed, Oct 08, 2025 at 04:38:16PM +0200, Carlos Maiolino wrote:
> >>> On Tue, Oct 07, 2025 at 02:58:02PM +0200, Johannes Thumshirn wrote:
> >>>> Add _create_zloop a helper function for creating a zloop device.
> >>>>
> >>>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> >>>> ---
> >>>>   common/zoned | 23 +++++++++++++++++++++++
> >>>>   1 file changed, 23 insertions(+)
> >>>>
> >>>> diff --git a/common/zoned b/common/zoned
> >>>> index 41697b08..33d3543b 100644
> >>>> --- a/common/zoned
> >>>> +++ b/common/zoned
> >>>> @@ -45,3 +45,26 @@ _require_zloop()
> >>>>   	    _notrun "This test requires zoned loopback device support"
> >>>>       fi
> >>>>   }
> >>>> +
> >>>> +# Create a zloop device
> >>>> +# useage: _create_zloop [id] <base_dir> <zone_size> <nr_conv_zones>
> >>>> +_create_zloop()
> >>>> +{
> >>>> +    local id=$1
> >>>> +
> >>>> +    if [ -n "$2" ]; then
> >>>> +        local base_dir=",base_dir=$2"
> >>>> +    fi
> >>>> +
> >>>> +    if [ -n "$3" ]; then
> >>>> +        local zone_size=",zone_size_mb=$3"
> >>>> +    fi
> >>>> +
> >>>> +    if [ -n "$4" ]; then
> >>>> +        local conv_zones=",conv_zones=$4"
> >>>> +    fi
> >>>> +
> >>>> +    local zloop_args="add id=$id$base_dir$zone_size$conv_zones"
> >>>> +
> >>>> +    echo "$zloop_args" > /dev/zloop-control
> >> Hmm, so the caller figures out its own /dev/zloopNNN number, passes NNN
> >> into the zloop-control devices, and then maybe a new bdev is created?
> >> Does NNN have to be one more than the current highest zloop device, or
> >> can it be any number?
> >>
> >> Source code says that if NNN >= 0 then it tries to create a new
> >> zloopNNN or fails with EEXIST; otherwise it gives you the lowest unused
> >> id.  It'd be nice in the second case if there were a way for the driver
> >> to tell you what the NNN is.
> >>
> >> The _create_zloop users seem to do an ls to select an NNN.  At a minimum
> >> that code probably ought to get hoisted to here as a common function (or
> >> maybe just put in _create_zloop itself).
> >>
> >> Or maybe turned into a loop like:
> >>
> >> 	while true; do
> >> 		local id=$(_next_zloop_id)
> >> 		err="$(echo "add id=$id$base_dir..." 2>&1 > /dev/zloop-control)"
> >> 		if [ -z "$err" ]; then
> >> 			echo "/dev/zloop$id"
> >> 			return 0
> >> 		fi
> >> 		if echo "$err" | ! grep -q "File exists"; then
> >> 			echo "$err" 1>&2
> >> 			return 1;
> >> 		fi
> >> 	done
> >>
> >> That way test cases don't have to do all that setup themselves?
> >>
> > Unfortunately the user has to create the zloop directory (e.g. 
> > BASE_DIR/0 for zloop0) beforehand (might be a bug though).
> 
> Not a bug. It is by design since the user can specify the ID of the zloop drive
> to create. And there is no fixed association between device ID and directory
> path to keep things flexible for the user/distro.

Hrmmm, each zloop device gets its own notion of the base dir, right?

> > What I could do is  encapsulate the find the next zloop and mkdir -p for 
> > the user (and call in _create_zloop if no id is supplied?)
> 
> Yes. Do that. The zloop directory si not something that the tests should touch
> anyway, so you should just define your own id <-> dir path mapping in the helpers.

That sounds fine to me...

--D

> 
> 
> -- 
> Damien Le Moal
> Western Digital Research
>