Re: [PATCH 17/18] lightnvm: allow to use full device path

[Igor Konopko <igor.j.konopko@intel.com>]

Matias,
any opinion from your side, whether you would like to do such a changes 
in userspace tool or in lightnvm core? I can go both ways.
Thanks
Igor

On 18.03.2019 15:41, Hans Holmberg wrote:
> On Mon, Mar 18, 2019 at 2:18 PM Igor Konopko <igor.j.konopko@intel.com> wrote:
>>
>>
>>
>> On 18.03.2019 11:28, Hans Holmberg wrote:
>>> On Thu, Mar 14, 2019 at 5:11 PM Igor Konopko <igor.j.konopko@intel.com> wrote:
>>>>
>>>> This patch adds the possibility to provide full device path (like
>>>> /dev/nvme0n1) when specifying device on top of which pblk instance
>>>> should be created/removed.
>>>>
>>>> This makes creation of targets from nvme-cli (or other ioctl based
>>>> tools) more unified with other commands in comparison with current
>>>> situation where almost all commands uses full device path with except
>>>> of lightnvm creation/removal parameter which uses just 'nvme0n1'
>>>> naming convention. After this changes both approach will be valid.
>>>>
>>>> Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
>>>> ---
>>>>    drivers/lightnvm/core.c | 23 ++++++++++++++++++-----
>>>>    1 file changed, 18 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/lightnvm/core.c b/drivers/lightnvm/core.c
>>>> index c01f83b..838c3d8 100644
>>>> --- a/drivers/lightnvm/core.c
>>>> +++ b/drivers/lightnvm/core.c
>>>> @@ -1195,6 +1195,21 @@ void nvm_unregister(struct nvm_dev *dev)
>>>>    }
>>>>    EXPORT_SYMBOL(nvm_unregister);
>>>>
>>>> +#define PREFIX_STR "/dev/"
>>>> +static void nvm_normalize_path(char *path)
>>>> +{
>>>> +       path[DISK_NAME_LEN - 1] = '\0';
>>>> +       if (!memcmp(PREFIX_STR, path,
>>>> +                               sizeof(char) * strlen(PREFIX_STR))) {
>>>> +               /*
>>>> +                * User provide name in '/dev/nvme0n1' format,
>>>> +                * so we need to skip '/dev/' for comparison
>>>> +                */
>>>> +               memmove(path, path + sizeof(char) * strlen(PREFIX_STR),
>>>> +                       (DISK_NAME_LEN - strlen(PREFIX_STR)) * sizeof(char));
>>>> +       }
>>>> +}
>>>> +
>>>
>>> I don't like this. Why add string parsing to the kernel? Can't this
>>> feature be added to the nvme tool?
>>
>> Since during target creation/removal in kernel, we already operate on
>> strings multiple times (strcmp calls for target types, nvme device,
>> target names) my idea was to keep this in the same layer too.
> 
> Oh, pardon the terse and rather grumpy review. Let me elaborate:
> 
> String parsing is best avoided when possible, and i don't think it's
> worth increasing the kernel code size and changing the behavior of the
> IOCTL when its fully doable to do this in userspace.
> 
> Thanks,
> Hans
> 
>>
>>>
>>>>    static int __nvm_configure_create(struct nvm_ioctl_create *create)
>>>>    {
>>>>           struct nvm_dev *dev;
>>>> @@ -1304,9 +1319,9 @@ static long nvm_ioctl_dev_create(struct file *file, void __user *arg)
>>>>                   return -EINVAL;
>>>>           }
>>>>
>>>> -       create.dev[DISK_NAME_LEN - 1] = '\0';
>>>> +       nvm_normalize_path(create.dev);
>>>> +       nvm_normalize_path(create.tgtname);
>>>>           create.tgttype[NVM_TTYPE_NAME_MAX - 1] = '\0';
>>>> -       create.tgtname[DISK_NAME_LEN - 1] = '\0';
>>>>
>>>>           if (create.flags != 0) {
>>>>                   __u32 flags = create.flags;
>>>> @@ -1333,7 +1348,7 @@ static long nvm_ioctl_dev_remove(struct file *file, void __user *arg)
>>>>           if (copy_from_user(&remove, arg, sizeof(struct nvm_ioctl_remove)))
>>>>                   return -EFAULT;
>>>>
>>>> -       remove.tgtname[DISK_NAME_LEN - 1] = '\0';
>>>> +       nvm_normalize_path(remove.tgtname);
>>>>
>>>>           if (remove.flags != 0) {
>>>>                   pr_err("nvm: no flags supported\n");
>>>> @@ -1373,8 +1388,6 @@ static long nvm_ioctl_dev_factory(struct file *file, void __user *arg)
>>>>           if (copy_from_user(&fact, arg, sizeof(struct nvm_ioctl_dev_factory)))
>>>>                   return -EFAULT;
>>>>
>>>> -       fact.dev[DISK_NAME_LEN - 1] = '\0';
>>>> -
>>>>           if (fact.flags & ~(NVM_FACTORY_NR_BITS - 1))
>>>>                   return -EINVAL;
>>>>
>>>> --
>>>> 2.9.5
>>>>