Re: [PATCH net-next v7 4/4] 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 <redacted>
Acked-by: Stanislav Fomichev <redacted>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
---
 .../userspace-api/ioctl/ioctl-number.rst      |  1 +
 fs/eventpoll.c                                | 72 +++++++++++++++++++
 include/uapi/linux/eventpoll.h                | 13 ++++
 3 files changed, 86 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 1b8d01af0c2c..aa58d42737e6 100644
--- a/fs/eventpoll.c
+++ b/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;
+
+               ep->busy_poll_usecs = epoll_params.busy_poll_usecs;