Joe Damato wrote: > On Wed, Jan 24, 2024 at 09:46:23PM -0500, Willem de Bruijn wrote: > > Joe Damato wrote: > > > Add an ioctl for getting and setting epoll_params. User programs can use > > > this ioctl to get and set the busy poll usec time or packet budget > > > params for a specific epoll context. > > > > > > Signed-off-by: Joe Damato <jdamato@xxxxxxxxxx> > > > > Please be sure to include the lists and people suggested by > > `get_maintainer.pl -f fs/eventpoll.c`. > > Thanks - I must have done something wrong when trying to get the maintainer > list. > > Should I resend this v2? Not sure what the appropriate thing to do is in > this case. My apologies. If you don't get additional feedback in a few days and still prefer this option that might be an approach. After reading the below thread, compare the different possible APIs and either revise the code or perhaps add a small paragraph why you think this is the preferred path. > > Adding ioctls is generally discouraged. > > > > As this affects the behavior of epoll_wait, should this just be a > > flag to (a new variant of) epoll_wait? > > I have no strong preference either way. It seems to me that adding a new > system call is a fairly significant change vs adding an ioctl, but I am > open to whatever is preferred by the maintainers. > > I have no idea who would need to weigh-in to make this decision. > > > Speaking from some experience with adding epoll_pwait2. I initially > > there added a stateful change that would affect wait behavior. The > > sensible feedback as the time was to just change the behavior of the > > syscall it affected. Even if that requires a syscall (which is not > > that different from an ioctl, if better defined). > > > > The discussion in that thread may be informative to decide on API: > > https://lwn.net/ml/linux-kernel/20201116161001.1606608-1-willemdebruijn.kernel@xxxxxxxxx/ > > Interesting thread, thanks for sending. > > > Agreed on the overall principle that it is preferable to be able to > > enable busypolling selectively. We already do for SO_BUSY_POLL and > > sysctl busy_read. > > Thanks for taking a look and providing feedback. > > > > > > --- > > > .../userspace-api/ioctl/ioctl-number.rst | 1 + > > > fs/eventpoll.c | 47 +++++++++++++++++++ > > > include/uapi/linux/eventpoll.h | 12 +++++ > > > 3 files changed, 60 insertions(+) > > > > > > diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst > > > index 457e16f06e04..b33918232f78 100644 > > > --- a/Documentation/userspace-api/ioctl/ioctl-number.rst > > > +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst > > > @@ -309,6 +309,7 @@ Code Seq# Include File Comments > > > 0x89 0B-DF linux/sockios.h > > > 0x89 E0-EF linux/sockios.h SIOCPROTOPRIVATE range > > > 0x89 F0-FF linux/sockios.h SIOCDEVPRIVATE range > > > +0x8A 00-1F linux/eventpoll.h > > > 0x8B all linux/wireless.h > > > 0x8C 00-3F WiNRADiO driver > > > <http://www.winradio.com.au/> > > > diff --git a/fs/eventpoll.c b/fs/eventpoll.c > > > index 40bd97477b91..c1ee0fe01da1 100644 > > > --- a/fs/eventpoll.c > > > +++ b/fs/eventpoll.c > > > @@ -6,6 +6,8 @@ > > > * Davide Libenzi <davidel@xxxxxxxxxxxxxxx> > > > */ > > > > > > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > > > + > > > #include <linux/init.h> > > > #include <linux/kernel.h> > > > #include <linux/sched/signal.h> > > > @@ -869,6 +871,49 @@ static void ep_clear_and_put(struct eventpoll *ep) > > > ep_free(ep); > > > } > > > > > > +static long ep_eventpoll_ioctl(struct file *file, unsigned int cmd, unsigned long arg) > > > +{ > > > + int ret; > > > + struct eventpoll *ep; > > > + struct epoll_params epoll_params; > > > + void __user *uarg = (void __user *) arg; > > > + > > > + if (!is_file_epoll(file)) > > > + return -EINVAL; > > > + > > > + ep = file->private_data; > > > + > > > + switch (cmd) { > > > +#ifdef CONFIG_NET_RX_BUSY_POLL > > > + case EPIOCSPARAMS: > > > + if (copy_from_user(&epoll_params, uarg, sizeof(epoll_params))) > > > + return -EFAULT; > > > + > > > + if (epoll_params.busy_poll_budget > NAPI_POLL_WEIGHT) > > > + pr_err("busy poll budget %u exceeds suggested maximum %u\n", > > > + epoll_params.busy_poll_budget, NAPI_POLL_WEIGHT); > > > + > > > + ep->busy_poll_usecs = epoll_params.busy_poll_usecs; > > > + ep->busy_poll_budget = epoll_params.busy_poll_budget; > > > + return 0; > > > + > > > + case EPIOCGPARAMS: > > > + memset(&epoll_params, 0, sizeof(epoll_params)); > > > + epoll_params.busy_poll_usecs = ep->busy_poll_usecs; > > > + epoll_params.busy_poll_budget = ep->busy_poll_budget; > > > + if (copy_to_user(uarg, &epoll_params, sizeof(epoll_params))) > > > + return -EFAULT; > > > + > > > + return 0; > > > +#endif > > > + default: > > > + ret = -EINVAL; > > > + break; > > > + } > > > + > > > + return ret; > > > +} > > > + > > > static int ep_eventpoll_release(struct inode *inode, struct file *file) > > > { > > > struct eventpoll *ep = file->private_data; > > > @@ -975,6 +1020,8 @@ static const struct file_operations eventpoll_fops = { > > > .release = ep_eventpoll_release, > > > .poll = ep_eventpoll_poll, > > > .llseek = noop_llseek, > > > + .unlocked_ioctl = ep_eventpoll_ioctl, > > > + .compat_ioctl = compat_ptr_ioctl, > > > }; > > > > > > /* > > > diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h > > > index cfbcc4cc49ac..8eb0fdbce995 100644 > > > --- a/include/uapi/linux/eventpoll.h > > > +++ b/include/uapi/linux/eventpoll.h > > > @@ -85,4 +85,16 @@ struct epoll_event { > > > __u64 data; > > > } EPOLL_PACKED; > > > > > > +struct epoll_params { > > > + u64 busy_poll_usecs; > > > + u16 busy_poll_budget; > > > + > > > + /* for future fields */ > > > + u8 data[118]; > > > +} EPOLL_PACKED; > > > + > > > +#define EPOLL_IOC_TYPE 0x8A > > > +#define EPIOCSPARAMS _IOW(EPOLL_IOC_TYPE, 0x01, struct epoll_params) > > > +#define EPIOCGPARAMS _IOR(EPOLL_IOC_TYPE, 0x02, struct epoll_params) > > > + > > > #endif /* _UAPI_LINUX_EVENTPOLL_H */ > > > -- > > > 2.25.1 > > > > > > >
