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

[Johannes Thumshirn <Johannes.Thumshirn@wdc.com>]

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).

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?)


Thoughts?