Linux: Add epoll ioctls

As of Linux kernel 6.9, some ioctls and a parameters structure have been
introduced which allow user programs to control whether a particular
epoll context will busy poll.

Update the headers to include these for the convenience of user apps.

The ioctls were added in Linux kernel 6.9 commit 18e2bf0edf4dd
("eventpoll: Add epoll ioctl for epoll_params") [1] to
include/uapi/linux/eventpoll.h.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/diff/?h=v6.9&id=18e2bf0edf4dd

Signed-off-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

3 files changed, 107 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 415aa1f..ae66590 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -200,6 +200,7 @@ tests += \
   tst-clone2 \
   tst-clone3 \
   tst-epoll \
+  tst-epoll-ioctls \
   tst-fanotify \
   tst-fdopendir-o_path \
   tst-getauxval \
diff --git a/sysdeps/unix/sysv/linux/sys/epoll.h b/sysdeps/unix/sysv/linux/sys/epoll.h
index fc8dce4..45e546f 100644
--- a/sysdeps/unix/sysv/linux/sys/epoll.h
+++ b/sysdeps/unix/sysv/linux/sys/epoll.h
@@ -19,6 +19,7 @@
 #define	_SYS_EPOLL_H	1
 
 #include <stdint.h>
+#include <sys/ioctl.h>
 #include <sys/types.h>
 
 #include <bits/types/sigset_t.h>
@@ -87,6 +88,19 @@ struct epoll_event
   epoll_data_t data;	/* User data variable */
 } __EPOLL_PACKED;
 
+struct epoll_params
+{
+  uint32_t busy_poll_usecs;
+  uint16_t busy_poll_budget;
+  uint8_t prefer_busy_poll;
+
+  /* pad the struct to a multiple of 64bits */
+  uint8_t __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)
 
 __BEGIN_DECLS
 
diff --git a/sysdeps/unix/sysv/linux/tst-epoll-ioctls.c b/sysdeps/unix/sysv/linux/tst-epoll-ioctls.c
new file mode 100644
index 0000000..618ecc4
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-epoll-ioctls.c
@@ -0,0 +1,92 @@
+/* Basic tests for Linux epoll ioctls.
+   Copyright (C) 2022-2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <intprops.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/process_state.h>
+#include <support/support.h>
+#include <support/test-driver.h>
+#include <support/xsignal.h>
+#include <support/xunistd.h>
+#include <sys/ioctl.h>
+#include <sys/epoll.h>
+
+static void
+test_epoll_ioctl (void)
+{
+  int efd = epoll_create1 (0);
+  TEST_VERIFY_EXIT (efd != -1);
+
+  struct epoll_params params;
+
+  TEST_COMPARE (ioctl (efd, EPIOCGPARAMS, &params), 0);
+
+  /* parameters are all 0 by default */
+  TEST_COMPARE (params.busy_poll_usecs, 0);
+  TEST_COMPARE (params.busy_poll_budget, 0);
+  TEST_COMPARE (params.prefer_busy_poll, 0);
+  TEST_COMPARE (params.__pad, 0);
+
+  /* set custom parameters */
+  params.busy_poll_usecs = 40;
+  params.busy_poll_budget = 8;
+  params.prefer_busy_poll = 1;
+  params.__pad = 0;
+
+  TEST_COMPARE (ioctl (efd, EPIOCSPARAMS, &params), 0);
+
+  memset (&params, 0, sizeof (params));
+
+  TEST_COMPARE (ioctl (efd, EPIOCGPARAMS, &params), 0);
+
+  /* check custom values were retrieved after being set */
+  TEST_COMPARE (params.busy_poll_usecs, 40);
+  TEST_COMPARE (params.busy_poll_budget, 8);
+  TEST_COMPARE (params.prefer_busy_poll, 1);
+  TEST_COMPARE (params.__pad, 0);
+
+  xclose (efd);
+}
+
+static bool
+ioctl_supported (void)
+{
+  int efd = epoll_create1 (0);
+  TEST_VERIFY_EXIT (efd != -1);
+
+  struct epoll_params params;
+  int r = ioctl (efd, EPIOCGPARAMS, &params);
+  xclose (efd);
+
+  return (r == 0);
+}
+
+static int
+do_test (void)
+{
+  if (ioctl_supported ())
+    test_epoll_ioctl ();
+  else
+    return EXIT_UNSUPPORTED;
+
+  return 0;
+}
+
+#include <support/test-driver.c>