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[24.6.151.244]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-703fd498a8fsm3002801b3a.109.2024.06.07.14.53.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Jun 2024 14:53:21 -0700 (PDT) Date: Fri, 7 Jun 2024 14:53:19 -0700 From: Joe Damato To: Alejandro Colomar Cc: linux-man@vger.kernel.org Subject: Re: [PATCH 1/1] ioctl_epoll.2: New page describing ioctl(2) operations for epoll fds Message-ID: References: <20240604181740.1741860-1-jdamato@fastly.com> <20240604181740.1741860-2-jdamato@fastly.com> Precedence: bulk X-Mailing-List: linux-man@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Jun 06, 2024 at 11:46:47PM +0200, Alejandro Colomar wrote: > On Thu, Jun 06, 2024 at 11:40:01PM GMT, Alejandro Colomar wrote: > > Hi Joe, > > > > On Tue, Jun 04, 2024 at 06:17:40PM GMT, Joe Damato wrote: > > > Signed-off-by: Joe Damato > > > > Thanks for the patch! Please see a few comments below. > > BTW, it triggers the following warning: > > $ make lint build check -j24 > GROTTY .tmp/man/man2/epoll_create.2.cat > GROTTY .tmp/man/man2/epoll_ctl.2.cat > TROFF .tmp/man/man2/ioctl_epoll.2.cat.set > an.tmac:.tmp/man/man2/ioctl_epoll.2:61: style: blank line in input > make: *** [/home/alx/src/linux/man-pages/man-pages/contrib/share/mk/build/catman/troff.mk:63: .tmp/man/man2/ioctl_epoll.2.cat.set] Error 1 > make: *** Deleting file '.tmp/man/man2/ioctl_epoll.2.cat.set' Hmm.. When I run make I get an error: $ make TROFF .tmp/man/man2/s390_sthyi.2.cat.set troff: .tmp/man/man2/s390_sthyi.2:124: warning [p 2, 2.8i]: cannot adjust line I tried to run the lint build check target and got an error about checkpatch: $ make lint build check -j8 CHECKPATCH .tmp/man/man2/fork.2.d/fork.c.lint-c.checkpatch.touch bash: line 1: checkpatch: command not found I have mandoc, groff, and clang-tidy installed, but maybe I'm missing other dependency? > > > > Have a lovely night! > > Alex > > > > > --- > > > man/man2/epoll_create.2 | 1 + > > > man/man2/epoll_ctl.2 | 1 + > > > man/man2/ioctl_epoll.2 | 203 ++++++++++++++++++++++++++++++++++++++++ > > > man/man7/epoll.7 | 1 + > > > 4 files changed, 206 insertions(+) > > > create mode 100644 man/man2/ioctl_epoll.2 > > > > > > diff --git a/man/man2/epoll_create.2 b/man/man2/epoll_create.2 > > > index f0327e8ba..2aa1745f5 100644 > > > --- a/man/man2/epoll_create.2 > > > +++ b/man/man2/epoll_create.2 > > > @@ -141,4 +141,5 @@ on overrun. > > > .BR close (2), > > > .BR epoll_ctl (2), > > > .BR epoll_wait (2), > > > +.BR ioctl_epoll (2), > > > .BR epoll (7) > > > diff --git a/man/man2/epoll_ctl.2 b/man/man2/epoll_ctl.2 > > > index 6d5bc032e..24bbe7405 100644 > > > --- a/man/man2/epoll_ctl.2 > > > +++ b/man/man2/epoll_ctl.2 > > > @@ -425,5 +425,6 @@ flag. > > > .SH SEE ALSO > > > .BR epoll_create (2), > > > .BR epoll_wait (2), > > > +.BR ioctl_epoll (2), > > > .BR poll (2), > > > .BR epoll (7) > > > diff --git a/man/man2/ioctl_epoll.2 b/man/man2/ioctl_epoll.2 > > > new file mode 100644 > > > index 000000000..1d53f458e > > > --- /dev/null > > > +++ b/man/man2/ioctl_epoll.2 > > > @@ -0,0 +1,203 @@ > > > +.\" Copyright (c) 2024, Joe Damato > > > +.\" Written by Joe Damato > > > +.\" > > > +.\" SPDX-License-Identifier: Linux-man-pages-copyleft > > > +.\" > > > +.\" > > > > Please use only one consecutive .\" > > > > > +.TH ioctl_epoll 2 (date) "Linux man-pages (unreleased)" > > > +.SH NAME > > > +ioctl_epoll \- ioctl() operations for epoll file descriptors > > > > Please add link pages and > > . > > > > > +.SH LIBRARY > > > +Standard C library > > > +.RI ( libc ", " \-lc ) > > > +.SH SYNOPSIS > > > +.nf > > > +.BR "#include " " /* Definition of " EPIOC* " constants and struct epoll_params */" > > > +.B "#include " > > > +.P > > > +.BI "int ioctl(int " fd ", int " op ", void " *argp ");" > > > > The '*' should be bold; not italics. > > > > > +.fi > > > +.SH DESCRIPTION > > > +Various > > > +.BR ioctl (2) > > > +operations can be performed on an epoll file descriptor (created by a call > > > +to > > > +.BR epoll_create (2)) > > > +(since Linux 6.9 and glibc 2.40) using calls of the form: > > > +.\" commit 18e2bf0edf4dd88d9656ec92395aa47392e85b61 > > > +.\" glibc commit 92c270d32caf3f8d5a02b8e46c7ec5d9d0315158 > > > +.P > > > +.in +4n > > > +.EX > > > +ioctl(fd, op, argp); > > > +.EE > > > +.in > > > +.P > > > +In the above, > > > +.I fd > > > +is a file descriptor referring to an epoll file descriptor obtained with a > > > +call to > > > +.BR epoll_create (2). > > > +.I op > > > +is one of the operations listed below, and > > > +.I argp > > > +is a pointer to the data structure described below. > > > > If argp is a pointer to a structure, then the prototype should document > > that: > > > > .BI "int ioctl(int " fd ", int " op ", struct epoll_params *" argp ); > > > > Also, I would document the two operations separately: > > > > .BI "int ioctl(int " fd ", EPIOCSPARAMS, const struct epoll_params *" argp ); > > .BI "int ioctl(int " fd ", EPIOCGPARAMS, struct epoll_params *" argp ); > > > > This allows documenting that the 'S' one doesn't modify the argp > > (AFAICS). > > > > > +.\" > > > +.P > > > +All supported > > > +.I op > > > +values (described below) use an > > > +.I argp > > > +argument which is a pointer to a > > > +.I epoll_params > > > +structure, defined as: > > > +.P > > > +.in +4n > > > +.EX > > > +struct epoll_params { > > > + uint32_t busy_poll_usecs; /* Number of usecs to busy poll */ > > > + uint16_t busy_poll_budget; /* Maximum number of packets to retrieve per poll */ > > > + uint8_t prefer_busy_poll; /* Boolean to enable or disable prefer busy poll */ > > > + > > The warning is triggered here. You should use a dummy character to > avoid the warning: > > \& > > > > + /* pad the struct to a multiple of 64bits */ > > > + uint8_t __pad; /* Must be zero */ > > > +}; > > > > You could add this type definition to the SYNOPSIS, below the function > > prototypes. > > > > > +.EE > > > +.in > > > +.P > > > +The > > > +.I busy_poll_usecs > > > +field denotes the number of microseconds that the network stack will busy > > > +poll. During this time period, the network device will be polled > > > +repeatedly. This value cannot exceed > > > +.B INT_MAX . > > > +.in > > > +.P > > > +The > > > +.I busy_poll_budget > > > +field denotes the maximum number of packets that the network stack will > > > +be retrieved on each poll attempt. This value cannot exceed > > > +.B NAPI_POLL_WEIGHT > > > +which, as of Linux 6.9, is 64, unless the process is run with > > > +.B CAP_NET_ADMIN . > > > +.P > > > +The > > > +.I prefer_busy_poll > > > +field is a boolean field and must be either 0 (disabled) or 1 (enabled). If > > > +enabled, this indicates to the network stack that busy poll is the > > > +preferred method of processing network data and the network stack should > > > +give the application the opportunity to busy poll. Without this option, > > > +very busy systems may continue to do network processing via the normal > > > +method of IRQs triggering softIRQ and NAPI. > > > +.P > > > +The supported > > > +.I op > > > +values: > > > +.TP > > > +.B EPIOCSPARAMS > > > +This operation allows the caller to specify an > > > +.I epoll_params > > > +structure to configure the operation of epoll. Refer to the structure > > > +description of the structure above to learn what configuration is > > > +supported. > > > +.TP > > > +.B EPIOCGPARAMS > > > +This operation allows the caller to retrieve the current > > > +.I epoll_params > > > +structure. This can be used to determine what the current settings are. > > > +.SH RETURN VALUE > > > +On success, 0 is returned. > > > +On failure, \-1 is returned, and > > > +.I errno > > > +is set to indicate the error. > > > +.SH ERRORS > > > +.TP > > > +.B EOPNOTSUPP > > > +The kernel was not compiled with busy poll support. > > > +.TP > > > +.B ENOIOCTLCMD > > > > Is this a thing? > > > > $ grep -rn ENOIOCTLCMD /usr/include/ > > $ > > > > I suspect this is EINVAL in user space? (Actually, you list the same > > exact error condition for EINVAL below.) > > > > > +The specified > > > +.I op > > > +is invalid. > > > +.TP > > > +.B EINVAL > > > +The > > > +.I fd > > > +specified is not an epoll file descriptor, or the > > > +.I op > > > +specified is invalid, or the > > > +.I __pad > > > +was not initialized to zero, or > > > +.I busy_poll_usecs > > > +exceeds > > > +.B INT_MAX , > > > +or > > > +.I prefer_busy_poll > > > +is not 0 or 1. > > > > Please separate the different conditions for EINVAL into separate > > entries. The ones that are related can go in the same one, but the > > unrelated ones are better split. > > > > > +.TP > > > +.B EPERM > > > +The process is being run without > > > +.I CAP_NET_ADMIN > > > > This should be bold. > > > > > +and the specified > > > +.I busy_poll_budget > > > > This should be > > > > .I argp.busy_poll_budget > > > > > +exceeds > > > +.I NAPI_POLL_WEIGHT > > > > This should be bold. > > > > > +(which is 64 as of Linux 6.9). > > > +.TP > > > +.B EFAULT > > > +.I argp > > > +does not point to a valid memory address. > > > +.SH EXAMPLES > > > +.EX > > > > Could you write an entire program, with a main()? > > > > If not, it's fine; this is better than nothing. But we prefer having > > entire programs that users can paste and try. > > > > > +/* Code to set the epoll params to enable busy polling */ > > > +\& > > > +int epollfd = epoll_create1(0); > > > +struct epoll_params params; > > > +\& > > > +if (epollfd == \-1) { > > > + perror("epoll_create1"); > > > + exit(EXIT_FAILURE); > > > +} > > > +\& > > > +memset(¶ms, 0, sizeof(struct epoll_params)); > > > +\& > > > +params.busy_poll_usecs = 25; > > > +params.busy_poll_budget = 8; > > > +params.prefer_busy_poll = 1; > > > +\& > > > +if (ioctl(epollfd, EPIOCSPARAMS, ¶ms) == \-1) { > > > + perror("ioctl"); > > > + exit(EXIT_FAILURE); > > > +} > > > +\& > > > +/* Code to show how to retrieve the current settings */ > > > +\& > > > +memset(¶ms, 0, sizeof(struct epoll_params)); > > > +\& > > > +if (ioctl(epollfd, EPIOCGPARAMS, ¶ms) == \-1) { > > > + perror("ioctl"); > > > + exit(EXIT_FAILURE); > > > +} > > > +\& > > > +/* params struct now contains the current parameters */ > > > +\& > > > +fprintf(stderr, "epoll usecs: %lu\\n", params.busy_poll_usecs); > > > +fprintf(stderr, "epoll packet budget: %u\\n", params.busy_poll_budget); > > > +fprintf(stderr, "epoll prefer busy poll: %u\\n", params.prefer_busy_poll); > > > +\& > > > +.SH History > > > +Linux 6.9. > > > +glibc 2.40. > > > +.SH SEE ALSO > > > +.BR ioctl (2), > > > +.BR epoll_create (2), > > > +.BR epoll_create1 (2), > > > +.BR epoll (7) > > > +.P > > > +.I Documentation/networking/napi.rst > > > +.P > > > +and > > > +.P > > > +.I Documentation/admin-guide/sysctl/net.rst > > > +.P > > > +in the Linux kernel source tree > > > > We could document that as > > > > .I linux.git/Documentation/... > > > > to not have to say "in the Linux kernel source tree". > > > > > diff --git a/man/man7/epoll.7 b/man/man7/epoll.7 > > > index e7892922e..4ad032bdd 100644 > > > --- a/man/man7/epoll.7 > > > +++ b/man/man7/epoll.7 > > > @@ -606,5 +606,6 @@ is present in an epoll instance. > > > .BR epoll_create1 (2), > > > .BR epoll_ctl (2), > > > .BR epoll_wait (2), > > > +.BR ioctl_epoll (2), > > > .BR poll (2), > > > .BR select (2) > > > -- > > > 2.34.1 > > > > > > > -- > > > > > > -- >