Re: [net-next v2 3/4] eventpoll: Add epoll ioctl for epoll_params
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: 2024-01-25 02:46:25
Also in:
lkml, netdev
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 <redacted>
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@gmail.com/ 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.
quoted hunk ↗ jump to hunk
--- .../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@xmailserver.org> */ +#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