On Sun, Jun 2, 2024 at 9:49 AM Huichun Feng <foxhoundsk.tw@xxxxxxxxx> wrote: > > In legacy sysfs GPIO, when using poll(2) on the sysfs GPIO value for > state change awaiting, a subsequent read(2) is required for consuming > the event, which the doc recommends the use of lseek(2) or > close-and-reopen to reset the file offset afterwards. > > The recommendations however, require at least 2 syscalls to consume > the event. Gladly, use of pread(2) require only 1 syscall for the > consumption. Let's advertise this usage by prioritizing its placement. > > Signed-off-by: Huichun Feng <foxhoundsk.tw@xxxxxxxxx> > --- > Documentation/userspace-api/gpio/sysfs.rst | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/Documentation/userspace-api/gpio/sysfs.rst b/Documentation/userspace-api/gpio/sysfs.rst > index 116921048..bd64896de 100644 > --- a/Documentation/userspace-api/gpio/sysfs.rst > +++ b/Documentation/userspace-api/gpio/sysfs.rst > @@ -97,9 +97,10 @@ and have the following read/write attributes: > poll(2) will return whenever the interrupt was triggered. If > you use poll(2), set the events POLLPRI and POLLERR. If you > use select(2), set the file descriptor in exceptfds. After > - poll(2) returns, either lseek(2) to the beginning of the sysfs > - file and read the new value or close the file and re-open it > - to read the value. > + poll(2) returns, use pread(2) to read the value at offset > + zero. Alternatively, either lseek(2) to the beginning of the > + sysfs file and read the new value or close the file and > + re-open it to read the value. > > "edge" ... > reads as either "none", "rising", "falling", or > -- > 2.34.1 > Please don't send new versions of a patch as responses in an email thread. Otherwise tools such as b4 cannot tell if it's a new version or part of a larger series. Please always start a new thread with get send-email or - better yet - start using b4 and let it manage the series for you. Please resend this correctly. Bart
