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List:       linux-rdma
Subject:    Re: [PATCH v11 23/26] block/rnbd: server: sysfs interface functions
From:       Danil Kipnis <danil.kipnis () cloud ! ionos ! com>
Date:       2020-03-30 13:14:46
Message-ID: CAHg0HuxsSJzth9iBotNSKJOG4327xRgSRgvaTMH6G58ADSXCTQ () mail ! gmail ! com
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On Sat, Mar 28, 2020 at 8:31 PM Bart Van Assche <bvanassche@acm.org> wrote:
>
> On 2020-03-20 05:16, Jack Wang wrote:
> > This is the sysfs interface to rnbd mapped devices on server side:
> >
> >   /sys/devices/virtual/rnbd-server/ctl/devices/<device_name>/
> >     |- block_dev
> >     |  *** link pointing to the corresponding block device sysfs entry
> >     |
> >     |- sessions/<session-name>/
> >     |  *** sessions directory
> >        |
> >        |- read_only
> >        |  *** is devices mapped as read only
> >        |
> >        |- mapping_path
> >           *** relative device path provided by the client during mapping
> >
>
> > +static struct kobj_type ktype = {
> > +     .sysfs_ops      = &kobj_sysfs_ops,
> > +};
>
> From Documentation/kobject.txt: "One important point cannot be
> overstated: every kobject must have a release() method." I think this is
> something that Greg KH feels very strongly about. Please fix this.

OK.


>
> > +int rnbd_srv_create_dev_sysfs(struct rnbd_srv_dev *dev,
> > +                            struct block_device *bdev,
> > +                            const char *dir_name)
> > +{
> > +     struct kobject *bdev_kobj;
> > +     int ret;
> > +
> > +     ret = kobject_init_and_add(&dev->dev_kobj, &ktype,
> > +                                rnbd_devs_kobj, dir_name);
> > +     if (ret)
> > +             return ret;
> > +
> > +     ret = kobject_init_and_add(&dev->dev_sessions_kobj,
> > +                                &ktype,
> > +                                &dev->dev_kobj, "sessions");
> > +     if (ret)
> > +             goto err;
> > +
> > +     bdev_kobj = &disk_to_dev(bdev->bd_disk)->kobj;
> > +     ret = sysfs_create_link(&dev->dev_kobj, bdev_kobj, "block_dev");
> > +     if (ret)
> > +             goto err2;
> > +
> > +     return 0;
> > +
> > +err2:
> > +     kobject_put(&dev->dev_sessions_kobj);
> > +err:
> > +     kobject_put(&dev->dev_kobj);
> > +     return ret;
> > +}
>
> Please choose more descriptive names for the goto labels, e.g.
> put_sess_kobj and put_dev_kobj.

OK


>
> > +static ssize_t read_only_show(struct kobject *kobj, struct kobj_attribute *attr,
> > +                           char *page)
> > +{
> > +     struct rnbd_srv_sess_dev *sess_dev;
> > +
> > +     sess_dev = container_of(kobj, struct rnbd_srv_sess_dev, kobj);
> > +
> > +     return scnprintf(page, PAGE_SIZE, "%s\n",
> > +                      (sess_dev->open_flags & FMODE_WRITE) ? "0" : "1");
> > +}
>
> The scnprintf() statement looks overcomplicated. How about the following?
>
> return scnprintf(page, PAGE_SIZE, "%d\n",
>                  (sess_dev->open_flags & FMODE_WRITE) != 0);

Looks better, thanks.


> > +void rnbd_srv_destroy_dev_session_sysfs(struct rnbd_srv_sess_dev *sess_dev)
> > +{
> > +     DECLARE_COMPLETION_ONSTACK(sysfs_compl);
> > +
> > +     sysfs_remove_group(&sess_dev->kobj,
> > +                        &rnbd_srv_default_dev_session_attr_group);
> > +
> > +     sess_dev->sysfs_release_compl = &sysfs_compl;
> > +     kobject_del(&sess_dev->kobj);
> > +     kobject_put(&sess_dev->kobj);
> > +     wait_for_completion(&sysfs_compl);
> > +}
>
> Why is there a wait_for_completion() call in the above function? I think
> Greg KH strongly disagrees with such calls in functions that remove
> sysfs attributes.

This just makes the function wait until the sysfs release function is
called, so that sess_dev can be freed afterwards. Will try to get rid
of the completion and call the rnbd_destroy_sess_dev() which frees the
struct directly from the release function.


>
> > +int rnbd_srv_create_sysfs_files(void)
> > +{
> > +     int err;
> > +
> > +     rnbd_dev_class = class_create(THIS_MODULE, "rnbd-server");
> > +     if (IS_ERR(rnbd_dev_class))
> > +             return PTR_ERR(rnbd_dev_class);
> > +
> > +     rnbd_dev = device_create(rnbd_dev_class, NULL,
> > +                               MKDEV(0, 0), NULL, "ctl");
> > +     if (IS_ERR(rnbd_dev)) {
> > +             err = PTR_ERR(rnbd_dev);
> > +             goto cls_destroy;
> > +     }
> > +     rnbd_devs_kobj = kobject_create_and_add("devices", &rnbd_dev->kobj);
> > +     if (!rnbd_devs_kobj) {
> > +             err = -ENOMEM;
> > +             goto dev_destroy;
> > +     }
> > +
> > +     return 0;
> > +
> > +dev_destroy:
> > +     device_destroy(rnbd_dev_class, MKDEV(0, 0));
> > +cls_destroy:
> > +     class_destroy(rnbd_dev_class);
> > +
> > +     return err;
> > +}
>
> Please mention the device class in the description of this patch.

OK,

Thanks,

Danil
>
> Thanks,
>
> Bart.
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