From: William Breathitt Gray <vilhelm.gray@gmail.com>
To: David Lechner <david@lechnology.com>
Cc: Jonathan Cameron <jic23@kernel.org>,
kernel@pengutronix.de, linux-stm32@st-md-mailman.stormreply.com,
a.fatoum@pengutronix.de, kamel.bouhara@bootlin.com,
gwendal@chromium.org, alexandre.belloni@bootlin.com,
linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com,
patrick.havelange@essensium.com, fabrice.gasnier@st.com,
mcoquelin.stm32@gmail.com, alexandre.torgue@st.com,
o.rempel@pengutronix.de
Subject: Re: [PATCH v8 20/22] counter: Implement events_queue_size sysfs attribute
Date: Sat, 27 Feb 2021 09:20:48 +0900 [thread overview]
Message-ID: <YDmQYK1lWXl7H5lm@shinobu> (raw)
In-Reply-To: <37ea96a2-d4a1-7d4c-a68a-8dc82896e86c@lechnology.com>
[-- Attachment #1: Type: text/plain, Size: 4807 bytes --]
On Fri, Feb 26, 2021 at 06:14:12PM -0600, David Lechner wrote:
> On 2/25/21 6:03 PM, William Breathitt Gray wrote:
> > On Sun, Feb 21, 2021 at 03:51:40PM +0000, Jonathan Cameron wrote:
> >> On Thu, 18 Feb 2021 19:32:16 +0900
> >> William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
> >>
> >>> On Sun, Feb 14, 2021 at 06:11:46PM +0000, Jonathan Cameron wrote:
> >>>> On Fri, 12 Feb 2021 21:13:44 +0900
> >>>> William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
> >>>>
> >>>>> The events_queue_size sysfs attribute provides a way for users to
> >>>>> dynamically configure the Counter events queue size for the Counter
> >>>>> character device interface. The size is in number of struct
> >>>>> counter_event data structures. The number of elements will be rounded-up
> >>>>> to a power of 2 due to a requirement of the kfifo_alloc function called
> >>>>> during reallocation of the queue.
> >>>>>
> >>>>> Cc: Oleksij Rempel <o.rempel@pengutronix.de>
> >>>>> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
> >>>>> ---
> >>>>> Documentation/ABI/testing/sysfs-bus-counter | 8 +++++++
> >>>>> drivers/counter/counter-chrdev.c | 23 +++++++++++++++++++
> >>>>> drivers/counter/counter-chrdev.h | 2 ++
> >>>>> drivers/counter/counter-sysfs.c | 25 +++++++++++++++++++++
> >>>>> 4 files changed, 58 insertions(+)
> >>>>>
> >>>>> diff --git a/Documentation/ABI/testing/sysfs-bus-counter b/Documentation/ABI/testing/sysfs-bus-counter
> >>>>> index 847e96f19d19..f6cb2a8b08a7 100644
> >>>>> --- a/Documentation/ABI/testing/sysfs-bus-counter
> >>>>> +++ b/Documentation/ABI/testing/sysfs-bus-counter
> >>>>> @@ -212,6 +212,14 @@ Description:
> >>>>> both edges:
> >>>>> Any state transition.
> >>>>>
> >>>>> +What: /sys/bus/counter/devices/counterX/events_queue_size
> >>>>> +KernelVersion: 5.13
> >>>>> +Contact: linux-iio@vger.kernel.org
> >>>>> +Description:
> >>>>> + Size of the Counter events queue in number of struct
> >>>>> + counter_event data structures. The number of elements will be
> >>>>> + rounded-up to a power of 2.
> >>>>> +
> >>>>> What: /sys/bus/counter/devices/counterX/name
> >>>>> KernelVersion: 5.2
> >>>>> Contact: linux-iio@vger.kernel.org
> >>>>> diff --git a/drivers/counter/counter-chrdev.c b/drivers/counter/counter-chrdev.c
> >>>>> index 16f02df7f73d..53eea894e13f 100644
> >>>>> --- a/drivers/counter/counter-chrdev.c
> >>>>> +++ b/drivers/counter/counter-chrdev.c
> >>>>> @@ -375,6 +375,29 @@ void counter_chrdev_remove(struct counter_device *const counter)
> >>>>> cdev_del(&counter->chrdev);
> >>>>> }
> >>>>>
> >>>>> +int counter_chrdev_realloc_queue(struct counter_device *const counter,
> >>>>> + size_t queue_size)
> >>>>> +{
> >>>>> + int err;
> >>>>> + DECLARE_KFIFO_PTR(events, struct counter_event);
> >>>>> + unsigned long flags;
> >>>>> +
> >>>>> + /* Allocate new events queue */
> >>>>> + err = kfifo_alloc(&events, queue_size, GFP_ATOMIC);
> >>>>
> >>>> Is there any potential for losing events?
> >>>
> >>> We take the events_list_lock down below so we're safe against missing an
> >>> event, but past events currently unread in the queue will be lost.
> >>>
> >>> Shortening the size of the queue is inherently a destructive process if
> >>> we have more events in the current queue than can fit in the new queue.
> >>> Because we a liable to lose some events in such a case, I think it's
> >>> best to keep the behavior of this reallocation consistent and have it
> >>> provide a fresh empty queue every time, as opposed to sometimes dropping
> >>> events and sometimes not.
> >>>
> >>> I also suspect an actual user would be setting the size of their queue
> >>> to the required amount before they begin watching events, rather than
> >>> adjusting it sporadically during a live operation.
> >>>
> >>
> >> Absolutely agree. As such I wonder if you are better off enforcing this
> >> behaviour? If the cdev is open for reading, don't allow the fifo to be
> >> resized.
> >>
> >> Jonathan
> >
> > I can't really think of a good reason not to, so let's enforce it: if
> > the cdev is open, then we'll return an EINVAL if the user attempts to
> > resize the queue.
> >
> > What is a good way to check for this condition? Should I just call
> > kref_read() and see if it's greater than 1? For example, in
> > counter_chrdev_realloc_queue():
> >
> > if (kref_read(&counter->dev.kobj.kref) > 1)
> > return -EINVAL;
> >
> > William Breathitt Gray
> >
>
> Wouldn't EBUSY make more sense?
Yes, EBUSY would be better here because the operation isn't necessarily
invalid, just unavailable because someone else has the cdev open.
William Breathitt Gray
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next prev parent reply other threads:[~2021-02-27 0:22 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-12 12:13 [PATCH v8 00/22] Introduce the Counter character device interface William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 01/22] docs: counter: Consolidate Counter sysfs attributes documentation William Breathitt Gray
2021-02-14 16:57 ` Jonathan Cameron
2021-02-15 11:05 ` William Breathitt Gray
2021-02-20 16:25 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 02/22] docs: counter: Fix spelling William Breathitt Gray
2021-02-20 16:26 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 03/22] counter: 104-quad-8: Return error when invalid mode during ceiling_write William Breathitt Gray
2021-02-20 16:30 ` David Lechner
2021-02-22 2:06 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 04/22] counter: 104-quad-8: Annotate hardware config module parameter William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 05/22] counter: 104-quad-8: Add const qualifiers for quad8_preset_register_set William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 06/22] counter: 104-quad-8: Add const qualifier for functions_list array William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 07/22] counter: 104-quad-8: Add const qualifier for actions_list array William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 08/22] counter: ftm-quaddec: " William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 09/22] counter: Return error code on invalid modes William Breathitt Gray
2021-02-14 17:07 ` Jonathan Cameron
2021-02-20 16:43 ` David Lechner
2021-02-22 4:42 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 10/22] counter: Standardize to ERANGE for limit exceeded errors William Breathitt Gray
2021-02-14 17:10 ` Jonathan Cameron
2021-02-16 1:26 ` William Breathitt Gray
2021-02-21 14:03 ` Jonathan Cameron
2021-02-20 16:48 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 11/22] counter: Rename counter_signal_value to counter_signal_level William Breathitt Gray
2021-02-20 16:52 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 12/22] counter: Rename counter_count_function to counter_function William Breathitt Gray
2021-02-14 17:13 ` Jonathan Cameron
2021-02-20 16:56 ` David Lechner
2021-02-23 5:14 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 13/22] counter: Internalize sysfs interface code William Breathitt Gray
2021-02-14 17:32 ` Jonathan Cameron
2021-02-20 17:50 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 14/22] counter: Update counter.h comments to reflect sysfs internalization William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 15/22] docs: counter: Update " William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 16/22] counter: Move counter enums to uapi header William Breathitt Gray
2021-02-20 23:55 ` David Lechner
2021-02-12 12:13 ` [PATCH v8 17/22] counter: Add character device interface William Breathitt Gray
2021-02-14 18:06 ` Jonathan Cameron
2021-02-24 5:34 ` William Breathitt Gray
2021-02-15 9:24 ` Oleksij Rempel
2021-02-16 1:53 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 18/22] docs: counter: Document " William Breathitt Gray
2021-02-14 17:48 ` Jonathan Cameron
2021-02-22 10:11 ` Pavel Machek
2021-02-26 0:27 ` William Breathitt Gray
2021-02-26 0:22 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 19/22] counter: Implement extension*_name sysfs attributes William Breathitt Gray
2021-02-14 18:09 ` Jonathan Cameron
2021-02-19 8:51 ` William Breathitt Gray
2021-02-21 14:05 ` Jonathan Cameron
2021-02-25 23:32 ` William Breathitt Gray
2021-02-27 15:14 ` Jonathan Cameron
2021-02-12 12:13 ` [PATCH v8 20/22] counter: Implement events_queue_size sysfs attribute William Breathitt Gray
2021-02-14 18:11 ` Jonathan Cameron
2021-02-18 10:32 ` William Breathitt Gray
2021-02-21 15:51 ` Jonathan Cameron
2021-02-26 0:03 ` William Breathitt Gray
2021-02-27 0:14 ` David Lechner
2021-02-27 0:20 ` William Breathitt Gray [this message]
2021-02-27 15:18 ` Jonathan Cameron
2021-02-28 2:46 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 21/22] counter: 104-quad-8: Replace mutex with spinlock William Breathitt Gray
2021-02-14 18:19 ` Jonathan Cameron
2021-02-16 2:16 ` William Breathitt Gray
2021-02-16 19:27 ` Jonathan Cameron
2021-02-18 10:16 ` William Breathitt Gray
2021-02-12 12:13 ` [PATCH v8 22/22] counter: 104-quad-8: Add IRQ support for the ACCES 104-QUAD-8 William Breathitt Gray
2021-02-14 18:24 ` Jonathan Cameron
2021-02-19 9:21 ` William Breathitt Gray
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