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SubjectRe: [PATCH v8 2/4] scsi: ufs: Introduce HPB feature
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On 2020-08-12 20:00, Daejun Park wrote:
> On 2020-08-06 02:11, Daejun Park wrote:
>>> +static int ufshpb_create_sysfs(struct ufs_hba *hba, struct ufshpb_lu *hpb)
>>> +{
>>> + int ret;
>>> +
>>> + ufshpb_stat_init(hpb);
>>> +
>>> + kobject_init(&hpb->kobj, &ufshpb_ktype);
>>> + mutex_init(&hpb->sysfs_lock);
>>> +
>>> + ret = kobject_add(&hpb->kobj, kobject_get(&hba->dev->kobj),
>>> + "ufshpb_lu%d", hpb->lun);
>>> +
>>> + if (ret)
>>> + return ret;
>>> +
>>> + ret = sysfs_create_group(&hpb->kobj, &ufshpb_sysfs_group);
>>> +
>>> + if (ret) {
>>> + dev_err(hba->dev, "ufshpb_lu%d create file error\n", hpb->lun);
>>> + return ret;
>>> + }
>>> +
>>> + dev_info(hba->dev, "ufshpb_lu%d sysfs adds uevent", hpb->lun);
>>> + kobject_uevent(&hpb->kobj, KOBJ_ADD);
>>> +
>>> + return 0;
>>> +}
>>
>> Please attach these sysfs attributes to /sys/class/scsi_device/*/device
>> instead of creating a new kobject. Consider using the following
>> scsi_host_template member to define LUN sysfs attributes:
>
> I am not rejecting your comment. But I added kobject for distinguishing
> between other attributes and attributes related to HPB feature.
> If you think it's pointless, I'll fix it.

Hi Daejun,

I see two reasons to add these sysfs attributes under
/sys/class/scsi_device/*/device:
- This makes the behavior of the UFS driver similar to that of other Linux
SCSI LLD drivers.
- This makes it easier for people who want to write udev rules that read
from these attributes. Since ufshpb_lu%d is attached to the UFS controller
it is not clear to me which attributes will appear first in sysfs - the
SCSI device attributes or the ufshpb_lu%d attributes. If there are only
SCSI device attributes there is no such ambiguity and hence authors of
udev rules won't have to worry about this race condition.

>>> +void ufshpb_remove(struct ufs_hba *hba)
>>> +{
>>> + struct ufshpb_lu *hpb, *n_hpb;
>>> + struct ufsf_feature_info *ufsf;
>>> + struct scsi_device *sdev;
>>> +
>>> + ufsf = &hba->ufsf;
>>> +
>>> + list_for_each_entry_safe(hpb, n_hpb, &lh_hpb_lu, list_hpb_lu) {
>>> + ufshpb_set_state(hpb, HPB_FAILED);
>>> +
>>> + sdev = hpb->sdev_ufs_lu;
>>> + sdev->hostdata = NULL;
>>> +
>>> + ufshpb_destroy_region_tbl(hpb);
>>> +
>>> + list_del_init(&hpb->list_hpb_lu);
>>> + ufshpb_remove_sysfs(hpb);
>>> +
>>> + kfree(hpb);
>>> + }
>>> +
>>> + dev_info(hba->dev, "ufshpb: remove success\n");
>>> +}
>>
>> Should the code in the body of the above loop perhaps be called from inside
>> ufshcd_slave_destroy()?
>
> Moving other stuffs in the loop is good idea, but removing attributes is problem.
> To avoid adding new kobject, I will try to use sysfs_merge_group()
> for adding attributes. To delete merged attributes, sysfs_unmerge_group()
> should be called. But sysfs_remove_groups() is called before calling ufshcd_slave_destroy().

Hmm ... I don't see why the sdev_groups host template attribute can't be used?

Please don't use sysfs_merge_group() and sysfs_unmerge_group() because that
would create a race condition against udev rules if these functions are called
after the device core has emitted a KOBJ_ADD event.

Thanks,

Bart.

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