epoll: add busy polling parameters

In Linux 6.9 a new ioctl for epoll was added:
https://man.archlinux.org/man/ioctl_eventpoll.2.en

Add support for it. The ioctls constants are padded to
64 bits alignment even on 32 bits machines.

Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>

(backport <#3922>)
(cherry picked from commit fb58c01)

Signed-off-by: Trevor Gross <tmgross@umich.edu>

Author: tammela

libc-test/build.rs

@@ -3864,6 +3864,9 @@ fn test_linux(target: &str) {
             // kernel so we can drop this and test the type once this new version is used in CI.
             "sched_attr" => true,
 
+            // FIXME: Requires >= 6.9 kernel headers.
+            "epoll_params" => true,
+
             _ => false,
         }
     });
@@ -4306,6 +4309,10 @@ fn test_linux(target: &str) {
             | "SCHED_FLAG_UTIL_CLAMP"
             | "SCHED_FLAG_ALL" if musl => true, // Needs more recent linux headers.
 
+            // FIXME: Requires >= 6.9 kernel headers.
+            "EPIOCSPARAMS"
+            | "EPIOCGPARAMS" => true,
+
             _ => false,
         }
     });

libc-test/semver/linux.txt

@@ -550,6 +550,8 @@ ENOTSUP
 ENOTUNIQ
 EOF
 EOWNERDEAD
+EPIOCGPARAMS
+EPIOCSPARAMS
 EPOLLERR
 EPOLLET
 EPOLLEXCLUSIVE
@@ -3489,6 +3491,7 @@ epoll_create
 epoll_create1
 epoll_ctl
 epoll_event
+epoll_params
 epoll_pwait
 epoll_wait
 erand48

src/unix/linux_like/linux/mod.rs

@@ -880,6 +880,15 @@ s! {
         pub salt: [::c_uchar; TLS_CIPHER_CHACHA20_POLY1305_SALT_SIZE],
         pub rec_seq: [::c_uchar; TLS_CIPHER_CHACHA20_POLY1305_REC_SEQ_SIZE],
     }
+
+    // #include <linux/eventpoll.h>
+
+    pub struct epoll_params {
+        pub busy_poll_usecs: u32,
+        pub busy_poll_budget: u16,
+        pub prefer_busy_poll: u8,
+        pub __pad: u8, // Must be zero
+    }
 }
 
 s_no_extra_traits! {
@@ -4936,6 +4945,10 @@ pub const SCHED_FLAG_ALL: ::c_int = SCHED_FLAG_RESET_ON_FORK
     | SCHED_FLAG_KEEP_ALL
     | SCHED_FLAG_UTIL_CLAMP;
 
+// ioctl_eventpoll: added in Linux 6.9
+pub const EPIOCSPARAMS: ::Ioctl = 0x40088a01;
+pub const EPIOCGPARAMS: ::Ioctl = 0x80088a02;
+
 f! {
     pub fn NLA_ALIGN(len: ::c_int) -> ::c_int {
         return ((len) + NLA_ALIGNTO - 1) & !(NLA_ALIGNTO - 1)