Re: working with IIO

[Lars-Peter Clausen <lars@metafoo.de>]

On 08/22/2013 05:48 PM, Drubin, Daniel wrote:
>
>
>> -----Original Message-----
>> From: Lars-Peter Clausen [mailto:lars@metafoo.de]
>> Sent: Thursday, August 22, 2013 6:42 PM
>> To: Drubin, Daniel
>> Cc: Jonathan Cameron; Yuniverg, Michael; linux-iio@vger.kernel.org;
>> Haimovich, Yoav
>> Subject: Re: working with IIO
>>
>> On 08/22/2013 05:16 PM, Drubin, Daniel wrote:
>>> [...]
>>>>>   From practical POV we don't have much choice (timeline), since we
>>>>> have to
>>>> reuse driver that is bound to IIO. From principle standpoint I
>>>> somehow fail to see a problem. It seems to me that all state handling
>>>> that an IIO driver needs to do is to keep associations of PIDs to
>>>> sensor rates, configure sensor to the highest rate in the list and
>>>> replicate shared data at rates requested by the clients. When a file
>>>> descriptor is closed (due to process termination or another reasons),
>>>> the actual sensor is re-configured with next-highest rate among the open
>> FDs.
>>>>
>>>> But you can't track the configured rate per PID with the current API.
>>>> That's why I keep saying that the API is stateless. You can not track
>>>> state per application without inventing a new API.
>>>
>>> Why can't I during keep a list of PIDs that currently use a sensor and record
>> current->pid together with "default" rate during the first sampling request
>> that doesn't have a matching PID, and in write_raw() handler that updates
>> rate match that current->pid against list of recorded PIDs? I didn't see a
>> possibility that sensor driver's handler may get called in a different context
>> than IIO core fops handler.
>>
>> So each time a process writes to a IIO sysfs file you want to record which
>> value that application wrote. So when I run `for i in `seq 0 100000`; do echo $i
>>> sampling_frequency; done` I'd end up with a list with one million entries
>> which will stay in the list forever.
>
> No, there is only one entry per PID. Next value that the same process writes will replace the previous one, not create a new entry. An entry will be create only if the write request arrived from a PID currently not in list.
>

Assume that echo is a /bin/echo, not a shell built-in command.

- Lars