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Subject: Re: dm: change dm_get_target_type() to check for module load error
To:     Mike Snitzer <snitzer@redhat.com>
Cc:     agk@redhat.com, dm-devel@redhat.com, linux-kernel@vger.kernel.org,
        Shuah Khan <skhan@linuxfoundation.org>
References: <20211004200641.378496-1-skhan@linuxfoundation.org>
 <YV4IecLg56NpzkYx@redhat.com>
From:   Shuah Khan <skhan@linuxfoundation.org>
Message-ID: <f1eebe07-492e-3152-8070-ea622d36bd33@linuxfoundation.org>
Date:   Wed, 6 Oct 2021 14:55:36 -0600
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On 10/6/21 2:35 PM, Mike Snitzer wrote:
> On Mon, Oct 04 2021 at  4:06P -0400,
> Shuah Khan <skhan@linuxfoundation.org> wrote:
> 
>> dm_get_target_type() doesn't check error return from request_module().
>> Change to check for error and return NULL instead of trying to get
>> target type again which would fail.
>>
>> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
>> ---
>>   drivers/md/dm-target.c | 11 ++++++++---
>>   1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/md/dm-target.c b/drivers/md/dm-target.c
>> index 64dd0b34fcf4..0789e9f91d3a 100644
>> --- a/drivers/md/dm-target.c
>> +++ b/drivers/md/dm-target.c
>> @@ -41,17 +41,22 @@ static struct target_type *get_target_type(const char *name)
>>   	return tt;
>>   }
>>   
>> -static void load_module(const char *name)
>> +static int load_module(const char *name)
>>   {
>> -	request_module("dm-%s", name);
>> +	return request_module("dm-%s", name);
>>   }
>>   
>>   struct target_type *dm_get_target_type(const char *name)
>>   {
>>   	struct target_type *tt = get_target_type(name);
>> +	int ret;
>>   
>>   	if (!tt) {
>> -		load_module(name);
>> +		ret = load_module(name);
>> +		if (ret < 0) {
>> +			pr_err("Module %s load failed %d\n", name, ret);
>> +			return NULL;
>> +		}
>>   		tt = get_target_type(name);
>>   	}
>>   
>> -- 
>> 2.30.2
>>
> 
> While I appreciate your intent, the reality is that multiple targets
> may be made available in a given module.  And so loading one dm module
> may bring in access to N targets.  There isn't a rigid 1:1 mapping of
> target modules to names.  And there may not even be a loadable module
> that has the name dm-${name} -- but that doesn't mean the target_type
> won;t have been loaded into DM for it to access.
> 

Thanks for the explanation.

-- Shuah