eventpoll: Add epoll ioctl for epoll_params

Add an ioctl for getting and setting epoll_params. User programs can use
this ioctl to get and set the busy poll usec time, packet budget, and
prefer busy poll params for a specific epoll context.

Parameters are limited:
  - busy_poll_usecs is limited to <= s32_max
  - busy_poll_budget is limited to <= NAPI_POLL_WEIGHT by unprivileged
    users (!capable(CAP_NET_ADMIN))
  - prefer_busy_poll must be 0 or 1
  - __pad must be 0
Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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/>

fs/eventpoll.c

@@ -37,6 +37,7 @@
 #include <linux/seq_file.h>
 #include <linux/compat.h>
 #include <linux/rculist.h>
+#include <linux/capability.h>
 #include <net/busy_poll.h>
 
 /*
@@ -494,6 +495,49 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
 	ep->napi_id = napi_id;
 }
 
+static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd,
+				  unsigned long arg)
+{
+	struct eventpoll *ep = file->private_data;
+	void __user *uarg = (void __user *)arg;
+	struct epoll_params epoll_params;
+
+	switch (cmd) {
+	case EPIOCSPARAMS:
+		if (copy_from_user(&epoll_params, uarg, sizeof(epoll_params)))
+			return -EFAULT;
+
+		/* pad byte must be zero */
+		if (epoll_params.__pad)
+			return -EINVAL;
+
+		if (epoll_params.busy_poll_usecs > S32_MAX)
+			return -EINVAL;
+
+		if (epoll_params.prefer_busy_poll > 1)
+			return -EINVAL;
+
+		if (epoll_params.busy_poll_budget > NAPI_POLL_WEIGHT &&
+		    !capable(CAP_NET_ADMIN))
+			return -EPERM;
+
+		WRITE_ONCE(ep->busy_poll_usecs, epoll_params.busy_poll_usecs);
+		WRITE_ONCE(ep->busy_poll_budget, epoll_params.busy_poll_budget);
+		WRITE_ONCE(ep->prefer_busy_poll, epoll_params.prefer_busy_poll);
+		return 0;
+	case EPIOCGPARAMS:
+		memset(&epoll_params, 0, sizeof(epoll_params));
+		epoll_params.busy_poll_usecs = READ_ONCE(ep->busy_poll_usecs);
+		epoll_params.busy_poll_budget = READ_ONCE(ep->busy_poll_budget);
+		epoll_params.prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll);
+		if (copy_to_user(uarg, &epoll_params, sizeof(epoll_params)))
+			return -EFAULT;
+		return 0;
+	default:
+		return -ENOIOCTLCMD;
+	}
+}
+
 #else
 
 static inline bool ep_busy_loop(struct eventpoll *ep, int nonblock)
@@ -505,6 +549,12 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
 {
 }
 
+static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd,
+				  unsigned long arg)
+{
+	return -EOPNOTSUPP;
+}
+
 #endif /* CONFIG_NET_RX_BUSY_POLL */
 
 /*
@@ -864,6 +914,27 @@ 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;
+
+	if (!is_file_epoll(file))
+		return -EINVAL;
+
+	switch (cmd) {
+	case EPIOCSPARAMS:
+	case EPIOCGPARAMS:
+		ret = ep_eventpoll_bp_ioctl(file, cmd, arg);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret;
+}
+
 static int ep_eventpoll_release(struct inode *inode, struct file *file)
 {
 	struct eventpoll *ep = file->private_data;
@@ -970,6 +1041,8 @@ 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,
 };
 
 /*

include/uapi/linux/eventpoll.h

@@ -85,4 +85,17 @@ struct epoll_event {
 	__u64 data;
 } EPOLL_PACKED;
 
+struct epoll_params {
+	__u32 busy_poll_usecs;
+	__u16 busy_poll_budget;
+	__u8 prefer_busy_poll;
+
+	/* pad the struct to a multiple of 64bits */
+	__u8 __pad;
+};
+
+#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 */