Convert poll/select to operate more directly on linux.PollFD

Current, doPoll copies the user struct pollfd array into a
[]syscalls.PollFD, which contains internal kdefs.FD and
waiter.EventMask types. While these are currently binary-compatible with
the Linux versions, we generally discourage copying directly to internal
types (someone may inadvertantly change kdefs.FD to uint64).

Instead, copy directly to a []linux.PollFD, which will certainly be
binary compatible. Most of syscalls/polling.go is included directly into
syscalls/linux/sys_poll.go, as it can then operate directly on
linux.PollFD. The additional syscalls.PollFD type is providing little
value.

I've also added explicit conversion functions for waiter.EventMask,
which creates the possibility of a different binary format.

PiperOrigin-RevId: 244042947
Change-Id: I24e5b642002a32b3afb95a9dcb80d4acd1288abf

1 files changed, 20 insertions, 6 deletions

diff --git a/pkg/waiter/waiter.go b/pkg/waiter/waiter.go
index fd429f733..a6c9dff3c 100644
--- a/pkg/waiter/waiter.go
+++ b/pkg/waiter/waiter.go
@@ -67,14 +67,28 @@ type EventMask uint16
 // Events that waiters can wait on. The meaning is the same as those in the
 // poll() syscall.
 const (
-	EventIn   EventMask = 0x01 // syscall.EPOLLIN
-	EventPri  EventMask = 0x02 // syscall.EPOLLPRI
-	EventOut  EventMask = 0x04 // syscall.EPOLLOUT
-	EventErr  EventMask = 0x08 // syscall.EPOLLERR
-	EventHUp  EventMask = 0x10 // syscall.EPOLLHUP
-	EventNVal EventMask = 0x20 // Not defined in syscall.
+	EventIn  EventMask = 0x01 // POLLIN
+	EventPri EventMask = 0x02 // POLLPRI
+	EventOut EventMask = 0x04 // POLLOUT
+	EventErr EventMask = 0x08 // POLLERR
+	EventHUp EventMask = 0x10 // POLLHUP
+
+	allEvents EventMask = 0x1f
 )
 
+// EventMaskFromLinux returns an EventMask representing the supported events
+// from the Linux events e, which is in the format used by poll(2).
+func EventMaskFromLinux(e uint32) EventMask {
+	// Our flag definitions are currently identical to Linux.
+	return EventMask(e) & allEvents
+}
+
+// ToLinux returns e in the format used by Linux poll(2).
+func (e EventMask) ToLinux() uint32 {
+	// Our flag definitions are currently identical to Linux.
+	return uint32(e)
+}
+
 // Waitable contains the methods that need to be implemented by waitable
 // objects.
 type Waitable interface {