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[72.189.64.225]) by smtp.gmail.com with ESMTPSA id 184sm27349qkl.34.2020.10.08.05.28.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Oct 2020 05:29:00 -0700 (PDT) Date: Thu, 8 Oct 2020 08:28:45 -0400 From: William Breathitt Gray To: Pavel Machek Cc: jic23@kernel.org, kamel.bouhara@bootlin.com, gwendal@chromium.org, alexandre.belloni@bootlin.com, david@lechnology.com, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, 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 Subject: Re: [PATCH v5 4/5] docs: counter: Document character device interface Message-ID: <20201008122845.GA3314@shinobu> References: <54190f9875b81b6aa5483a7710b084053a44abb8.1601170670.git.vilhelm.gray@gmail.com> <20201008080909.GA31561@amd> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="/04w6evG8XlLl3ft" Content-Disposition: inline In-Reply-To: <20201008080909.GA31561@amd> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --/04w6evG8XlLl3ft Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Oct 08, 2020 at 10:09:09AM +0200, Pavel Machek wrote: > Hi! >=20 > > + int main(void) > > + { > > + struct pollfd pfd =3D { .events =3D POLLIN }; > > + struct counter_event event_data[2]; > > + > > + pfd.fd =3D open("/dev/counter0", O_RDWR); > > + > > + ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches); > > + ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches + 1); > > + ioctl(pfd.fd, COUNTER_LOAD_WATCHES_IOCTL); > > + > > + for (;;) { > > + poll(&pfd, 1, -1); >=20 > Why do poll, when you are doing blocking read? >=20 > > + read(pfd.fd, event_data, sizeof(event_data)); >=20 > Does your new chrdev always guarantee returning complete buffer? >=20 > If so, should it behave like that? >=20 > Best regards, > Pavel > --=20 > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/b= log.html I suppose you're right: a poll() should be redundant now with this version of the character device implementation because buffers will always return complete; so a blocking read() should achieve the same behavior that a poll() with read() would. I'll give some more time for additional feedback to come in for this version of the patchset, and then likely remove support for poll() in the v6 submission. 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