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`. 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? 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/ 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. > --- > .../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 >
