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Date:   Sat, 14 Nov 2020 15:32:34 +0000
From:   Jonathan Cameron <jic23@jic23.retrosnub.co.uk>
To:     Alexandru Ardelean <ardeleanalex@gmail.com>
Cc:     Alexandru Ardelean <alexandru.ardelean@analog.com>,
        linux-iio <linux-iio@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] iio: core: centralize ioctl() calls to the main chardev
Message-ID: <20201114153234.0fa226df@archlinux>
In-Reply-To: <20201114153023.415bea0e@archlinux>
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        <20200925133805.062c0b1c@archlinux>
        <CA+U=DsqVomxim2SVqkC8LVYguUaSv-w0kw-B-shz7S0Yeka6Gg@mail.gmail.com>
        <20201114153023.415bea0e@archlinux>
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On Sat, 14 Nov 2020 15:30:23 +0000
Jonathan Cameron <jic23@kernel.org> wrote:

> On Mon, 2 Nov 2020 08:59:57 +0200
> Alexandru Ardelean <ardeleanalex@gmail.com> wrote:
> 
> > On Fri, Sep 25, 2020 at 3:38 PM Jonathan Cameron <jic23@kernel.org> wrote:  
> > >
> > > On Thu, 24 Sep 2020 11:41:55 +0300
> > > Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:
> > >    
> > > > The aim of this is to improve a bit the organization of ioctl() calls in
> > > > IIO core. Currently the chardev is split across IIO core sub-modules/files.
> > > > The main chardev has to be able to handle ioctl() calls, and if we need to
> > > > add buffer ioctl() calls, this would complicate things.
> > > >
> > > > The 'industrialio-core.c' file will provide a 'iio_device_ioctl()' which
> > > > will iterate over a list of ioctls registered with the IIO device. These
> > > > can be event ioctl() or buffer ioctl() calls, or something else.
> > > >
> > > > Each ioctl() handler will have to return a IIO_IOCTL_UNHANDLED code (which
> > > > is positive 1), if the ioctl() did not handle the call in any. This
> > > > eliminates any potential ambiguities about negative error codes, which
> > > > should fail the call altogether.
> > > >
> > > > If any ioctl() returns 0, it was considered that it was serviced
> > > > successfully and the loop will exit.
> > > >
> > > > This change also moves the handling of the IIO_GET_EVENT_FD_IOCTL command
> > > > inside 'industrialio-event.c', where this is better suited.
> > > >
> > > > This patch is a combination of 2 other patches from an older series:
> > > > Patch 1: iio: core: add simple centralized mechanism for ioctl() handlers
> > > >   Link: https://lore.kernel.org/linux-iio/20200427131100.50845-6-alexandru.ardelean@analog.com/
> > > > Patch 2: iio: core: use new common ioctl() mechanism
> > > >   Link: https://lore.kernel.org/linux-iio/20200427131100.50845-7-alexandru.ardelean@analog.com/
> > > >
> > > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> > > > ---
> > > >
> > > > Note: since this is a change to the IIO core, we don't need to put this in
> > > > right now; especially if there is a tight schedule, or we are too close to
> > > > a merge window.    
> > >
> > > Looks good to me.  As you suggest, lets let this one sit on the list for a
> > > while though!    
> > 
> > ping on this  
> 
> Thanks.  Was still on my list, but I've been lazy and not been clearing that
> out for a while - too many scary things there :)
> 
> Anyhow, applied to the togreg branch of iio.git and pushed out as testing for
> all the normal reasons.
Hmm. I should really wait for local build tests to finish.  Tweaked to
remove the bonus @ where you have @@ in the docs.

Note I'm build testing with W=1 these days that finds this sort of docs
issue.

thanks,

Jonathan

> 
> Thanks,
> 
> Jonathan
> 
> > 
> > thanks
> > Alex
> >   
> > >
> > > Jonathan
> > >    
> > > >
> > > >  drivers/iio/iio_core.h           | 15 ++++++++-
> > > >  drivers/iio/industrialio-core.c  | 56 ++++++++++++++++++++++++--------
> > > >  drivers/iio/industrialio-event.c | 28 +++++++++++++++-
> > > >  include/linux/iio/iio-opaque.h   |  2 ++
> > > >  4 files changed, 85 insertions(+), 16 deletions(-)
> > > >
> > > > diff --git a/drivers/iio/iio_core.h b/drivers/iio/iio_core.h
> > > > index fd9a5f1d5e51..fced02cadcc3 100644
> > > > --- a/drivers/iio/iio_core.h
> > > > +++ b/drivers/iio/iio_core.h
> > > > @@ -17,6 +17,20 @@ struct iio_dev;
> > > >
> > > >  extern struct device_type iio_device_type;
> > > >
> > > > +#define IIO_IOCTL_UNHANDLED  1
> > > > +struct iio_ioctl_handler {
> > > > +     struct list_head entry;
> > > > +     long (*ioctl)(struct iio_dev *indio_dev, struct file *filp,
> > > > +                   unsigned int cmd, unsigned long arg);
> > > > +};
> > > > +
> > > > +long iio_device_ioctl(struct iio_dev *indio_dev, struct file *filp,
> > > > +                   unsigned int cmd, unsigned long arg);
> > > > +
> > > > +void iio_device_ioctl_handler_register(struct iio_dev *indio_dev,
> > > > +                                    struct iio_ioctl_handler *h);
> > > > +void iio_device_ioctl_handler_unregister(struct iio_ioctl_handler *h);
> > > > +
> > > >  int __iio_add_chan_devattr(const char *postfix,
> > > >                          struct iio_chan_spec const *chan,
> > > >                          ssize_t (*func)(struct device *dev,
> > > > @@ -74,7 +88,6 @@ static inline void iio_buffer_wakeup_poll(struct iio_dev *indio_dev) {}
> > > >  int iio_device_register_eventset(struct iio_dev *indio_dev);
> > > >  void iio_device_unregister_eventset(struct iio_dev *indio_dev);
> > > >  void iio_device_wakeup_eventset(struct iio_dev *indio_dev);
> > > > -int iio_event_getfd(struct iio_dev *indio_dev);
> > > >
> > > >  struct iio_event_interface;
> > > >  bool iio_event_enabled(const struct iio_event_interface *ev_int);
> > > > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> > > > index 261d3b17edc9..964a0a2d6f8b 100644
> > > > --- a/drivers/iio/industrialio-core.c
> > > > +++ b/drivers/iio/industrialio-core.c
> > > > @@ -1567,6 +1567,7 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
> > > >       }
> > > >       dev_set_name(&dev->dev, "iio:device%d", dev->id);
> > > >       INIT_LIST_HEAD(&iio_dev_opaque->buffer_list);
> > > > +     INIT_LIST_HEAD(&iio_dev_opaque->ioctl_handlers);
> > > >
> > > >       return dev;
> > > >  }
> > > > @@ -1660,26 +1661,47 @@ static int iio_chrdev_release(struct inode *inode, struct file *filp)
> > > >       return 0;
> > > >  }
> > > >
> > > > -/* Somewhat of a cross file organization violation - ioctls here are actually
> > > > - * event related */
> > > > +void iio_device_ioctl_handler_register(struct iio_dev *indio_dev,
> > > > +                                    struct iio_ioctl_handler *h)
> > > > +{
> > > > +     struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > > > +
> > > > +     list_add_tail(&h->entry, &iio_dev_opaque->ioctl_handlers);
> > > > +}
> > > > +
> > > > +void iio_device_ioctl_handler_unregister(struct iio_ioctl_handler *h)
> > > > +{
> > > > +     list_del(&h->entry);
> > > > +}
> > > > +
> > > >  static long iio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> > > >  {
> > > >       struct iio_dev *indio_dev = filp->private_data;
> > > > -     int __user *ip = (int __user *)arg;
> > > > -     int fd;
> > > > +     struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > > > +     struct iio_ioctl_handler *h;
> > > > +     int ret = -ENODEV;
> > > > +
> > > > +     mutex_lock(&indio_dev->info_exist_lock);
> > > >
> > > > +     /**
> > > > +      * The NULL check here is required to prevent crashing when a device
> > > > +      * is being removed while userspace would still have open file handles
> > > > +      * to try to access this device.
> > > > +      */
> > > >       if (!indio_dev->info)
> > > > -             return -ENODEV;
> > > > -
> > > > -     if (cmd == IIO_GET_EVENT_FD_IOCTL) {
> > > > -             fd = iio_event_getfd(indio_dev);
> > > > -             if (fd < 0)
> > > > -                     return fd;
> > > > -             if (copy_to_user(ip, &fd, sizeof(fd)))
> > > > -                     return -EFAULT;
> > > > -             return 0;
> > > > +             goto out_unlock;
> > > > +
> > > > +     ret = -EINVAL;
> > > > +     list_for_each_entry(h, &iio_dev_opaque->ioctl_handlers, entry) {
> > > > +             ret = h->ioctl(indio_dev, filp, cmd, arg);
> > > > +             if (ret != IIO_IOCTL_UNHANDLED)
> > > > +                     break;
> > > >       }
> > > > -     return -EINVAL;
> > > > +
> > > > +out_unlock:
> > > > +     mutex_unlock(&indio_dev->info_exist_lock);
> > > > +
> > > > +     return ret;
> > > >  }
> > > >
> > > >  static const struct file_operations iio_buffer_fileops = {
> > > > @@ -1796,6 +1818,9 @@ EXPORT_SYMBOL(__iio_device_register);
> > > >   **/
> > > >  void iio_device_unregister(struct iio_dev *indio_dev)
> > > >  {
> > > > +     struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > > > +     struct iio_ioctl_handler *h, *t;
> > > > +
> > > >       cdev_device_del(&indio_dev->chrdev, &indio_dev->dev);
> > > >
> > > >       mutex_lock(&indio_dev->info_exist_lock);
> > > > @@ -1806,6 +1831,9 @@ void iio_device_unregister(struct iio_dev *indio_dev)
> > > >
> > > >       indio_dev->info = NULL;
> > > >
> > > > +     list_for_each_entry_safe(h, t, &iio_dev_opaque->ioctl_handlers, entry)
> > > > +             list_del(&h->entry);
> > > > +
> > > >       iio_device_wakeup_eventset(indio_dev);
> > > >       iio_buffer_wakeup_poll(indio_dev);
> > > >
> > > > diff --git a/drivers/iio/industrialio-event.c b/drivers/iio/industrialio-event.c
> > > > index 99ba657b8568..a2de2fd89067 100644
> > > > --- a/drivers/iio/industrialio-event.c
> > > > +++ b/drivers/iio/industrialio-event.c
> > > > @@ -31,6 +31,7 @@
> > > >   * @flags:           file operations related flags including busy flag.
> > > >   * @group:           event interface sysfs attribute group
> > > >   * @read_lock:               lock to protect kfifo read operations
> > > > + * @@ioctl_handler:  handler for event ioctl() calls
> > > >   */
> > > >  struct iio_event_interface {
> > > >       wait_queue_head_t       wait;
> > > > @@ -40,6 +41,7 @@ struct iio_event_interface {
> > > >       unsigned long           flags;
> > > >       struct attribute_group  group;
> > > >       struct mutex            read_lock;
> > > > +     struct iio_ioctl_handler        ioctl_handler;
> > > >  };
> > > >
> > > >  bool iio_event_enabled(const struct iio_event_interface *ev_int)
> > > > @@ -187,7 +189,7 @@ static const struct file_operations iio_event_chrdev_fileops = {
> > > >       .llseek = noop_llseek,
> > > >  };
> > > >
> > > > -int iio_event_getfd(struct iio_dev *indio_dev)
> > > > +static int iio_event_getfd(struct iio_dev *indio_dev)
> > > >  {
> > > >       struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > > >       struct iio_event_interface *ev_int = iio_dev_opaque->event_interface;
> > > > @@ -473,6 +475,24 @@ static void iio_setup_ev_int(struct iio_event_interface *ev_int)
> > > >       mutex_init(&ev_int->read_lock);
> > > >  }
> > > >
> > > > +static long iio_event_ioctl(struct iio_dev *indio_dev, struct file *filp,
> > > > +                         unsigned int cmd, unsigned long arg)
> > > > +{
> > > > +     int __user *ip = (int __user *)arg;
> > > > +     int fd;
> > > > +
> > > > +     if (cmd == IIO_GET_EVENT_FD_IOCTL) {
> > > > +             fd = iio_event_getfd(indio_dev);
> > > > +             if (fd < 0)
> > > > +                     return fd;
> > > > +             if (copy_to_user(ip, &fd, sizeof(fd)))
> > > > +                     return -EFAULT;
> > > > +             return 0;
> > > > +     }
> > > > +
> > > > +     return IIO_IOCTL_UNHANDLED;
> > > > +}
> > > > +
> > > >  static const char *iio_event_group_name = "events";
> > > >  int iio_device_register_eventset(struct iio_dev *indio_dev)
> > > >  {
> > > > @@ -526,6 +546,10 @@ int iio_device_register_eventset(struct iio_dev *indio_dev)
> > > >               ev_int->group.attrs[attrn++] = &p->dev_attr.attr;
> > > >       indio_dev->groups[indio_dev->groupcounter++] = &ev_int->group;
> > > >
> > > > +     ev_int->ioctl_handler.ioctl = iio_event_ioctl;
> > > > +     iio_device_ioctl_handler_register(&iio_dev_opaque->indio_dev,
> > > > +                                       &ev_int->ioctl_handler);
> > > > +
> > > >       return 0;
> > > >
> > > >  error_free_setup_event_lines:
> > > > @@ -558,6 +582,8 @@ void iio_device_unregister_eventset(struct iio_dev *indio_dev)
> > > >
> > > >       if (ev_int == NULL)
> > > >               return;
> > > > +
> > > > +     iio_device_ioctl_handler_unregister(&ev_int->ioctl_handler);
> > > >       iio_free_chan_devattr_list(&ev_int->dev_attr_list);
> > > >       kfree(ev_int->group.attrs);
> > > >       kfree(ev_int);
> > > > diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h
> > > > index f2e94196d31f..07c5a8e52ca8 100644
> > > > --- a/include/linux/iio/iio-opaque.h
> > > > +++ b/include/linux/iio/iio-opaque.h
> > > > @@ -11,6 +11,7 @@
> > > >   * @channel_attr_list:               keep track of automatically created channel
> > > >   *                           attributes
> > > >   * @chan_attr_group:         group for all attrs in base directory
> > > > + * @ioctl_handlers:          ioctl handlers registered with the core handler
> > > >   * @debugfs_dentry:          device specific debugfs dentry
> > > >   * @cached_reg_addr:         cached register address for debugfs reads
> > > >   * @read_buf:                        read buffer to be used for the initial reg read
> > > > @@ -22,6 +23,7 @@ struct iio_dev_opaque {
> > > >       struct list_head                buffer_list;
> > > >       struct list_head                channel_attr_list;
> > > >       struct attribute_group          chan_attr_group;
> > > > +     struct list_head                ioctl_handlers;
> > > >  #if defined(CONFIG_DEBUG_FS)
> > > >       struct dentry                   *debugfs_dentry;
> > > >       unsigned                        cached_reg_addr;    
> > >    
>