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

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

On 10/13/25 5:08 PM, Darrick J. Wong wrote:
> 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?
There is the base dir and underneath there is $BASE_DIR/$ID and this 
directory has to exist at the time of adding the device.