Implement `fcntl` options `F_GETSIG` and `F_SETSIG`.

These options allow overriding the signal that gets sent to the process when
I/O operations are available on the file descriptor, rather than the default
`SIGIO` signal. Doing so also populates `siginfo` to contain extra information
about which file descriptor caused the event (`si_fd`) and what events happened
on it (`si_band`). The logic around which FD is populated within `si_fd`
matches Linux's, which means it has some weird edge cases where that value may
not actually refer to a file descriptor that is still valid.

This CL also ports extra S/R logic regarding async handler in VFS2.
Without this, async I/O handlers aren't properly re-registered after S/R.

PiperOrigin-RevId: 345436598

1 files changed, 3 insertions, 4 deletions

diff --git a/pkg/sentry/kernel/epoll/epoll.go b/pkg/sentry/kernel/epoll/epoll.go
index 15519f0df..61aeca044 100644
--- a/pkg/sentry/kernel/epoll/epoll.go
+++ b/pkg/sentry/kernel/epoll/epoll.go
@@ -273,7 +273,7 @@ func (e *EventPoll) ReadEvents(max int) []linux.EpollEvent {
 //
 // Callback is called when one of the files we're polling becomes ready. It
 // moves said file to the readyList if it's currently in the waiting list.
-func (p *pollEntry) Callback(*waiter.Entry) {
+func (p *pollEntry) Callback(*waiter.Entry, waiter.EventMask) {
 	e := p.epoll
 
 	e.listsMu.Lock()
@@ -306,9 +306,8 @@ func (e *EventPoll) initEntryReadiness(entry *pollEntry) {
 	f.EventRegister(&entry.waiter, entry.mask)
 
 	// Check if the file happens to already be in a ready state.
-	ready := f.Readiness(entry.mask) & entry.mask
-	if ready != 0 {
-		entry.Callback(&entry.waiter)
+	if ready := f.Readiness(entry.mask) & entry.mask; ready != 0 {
+		entry.Callback(&entry.waiter, ready)
 	}
 }