On Tue, Mar 31, 2015 at 11:31:22PM +0200, Christian Riesch wrote:
> The PPS_FETCH ioctl in drivers/pps/pps.c blocks until a new PPS event
> occurs, then returns the time stamp data. While this is fine for
> lots of applications, sometimes it would be nice if the poll system
> call and a subsequent read could be used to obtain the pps data.
Nak. The read syscall can't be forced to return fix amount of
data.
Use a dedicated ioctl instead.
Ciao,
Rodolfo
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Hi Rodolfo,
Thanks for your reply!
On Wed, Apr 1, 2015 at 10:11 AM, Rodolfo Giometti <[email protected]> wrote:
> On Tue, Mar 31, 2015 at 11:31:22PM +0200, Christian Riesch wrote:
>> The PPS_FETCH ioctl in drivers/pps/pps.c blocks until a new PPS event
>> occurs, then returns the time stamp data. While this is fine for
>> lots of applications, sometimes it would be nice if the poll system
>> call and a subsequent read could be used to obtain the pps data.
>
> Nak. The read syscall can't be forced to return fix amount of
> data.
I just copied/modified the behavior of ptp_read() in drivers/ptp/ptp_chardev.c:
if (cnt % sizeof(struct ptp_extts_event) != 0)
return -EINVAL;
There the amount of data is forced to be a multiple of sizeof(struct
ptp_extts_event). But if you prefer an ioctl, I can change that of
course.
>
> Use a dedicated ioctl instead.
Is it ok to pair POLLIN | POLLRDNORM in the poll function with an
ioctl? Or should returning POLLIN | POLLRDNORM mean that a read() will
not block? Should I use POLLPRI instead or something else?
Regards, Christian
[sent again with Rodolfo in the list of recipients, something went
wrong, sorry!]
Hi Rodolfo,
Thanks for your reply!
On Wed, Apr 1, 2015 at 10:11 AM, Rodolfo Giometti <[email protected]> wrote:
> On Tue, Mar 31, 2015 at 11:31:22PM +0200, Christian Riesch wrote:
>> The PPS_FETCH ioctl in drivers/pps/pps.c blocks until a new PPS event
>> occurs, then returns the time stamp data. While this is fine for
>> lots of applications, sometimes it would be nice if the poll system
>> call and a subsequent read could be used to obtain the pps data.
>
> Nak. The read syscall can't be forced to return fix amount of
> data.
I just copied/modified the behavior of ptp_read() in drivers/ptp/ptp_chardev.c:
if (cnt % sizeof(struct ptp_extts_event) != 0)
return -EINVAL;
There the amount of data is forced to be a multiple of sizeof(struct
ptp_extts_event). But if you prefer an ioctl, I can change that of
course.
> Use a dedicated ioctl instead.
Is it ok to pair POLLIN | POLLRDNORM in the poll function with an
ioctl? Or should returning POLLIN | POLLRDNORM mean that a read() will
not block? Should I use POLLPRI instead or something else?
Regards, Christian