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, 18 insertions, 1 deletions

diff --git a/pkg/sentry/vfs/save_restore.go b/pkg/sentry/vfs/save_restore.go
index 7723ed643..8f070ed53 100644
--- a/pkg/sentry/vfs/save_restore.go
+++ b/pkg/sentry/vfs/save_restore.go
@@ -18,8 +18,10 @@ import (
 	"fmt"
 	"sync/atomic"
 
+	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/refsvfs2"
+	"gvisor.dev/gvisor/pkg/waiter"
 )
 
 // FilesystemImplSaveRestoreExtension is an optional extension to
@@ -120,5 +122,20 @@ func (mnt *Mount) afterLoad() {
 func (epi *epollInterest) afterLoad() {
 	// Mark all epollInterests as ready after restore so that the next call to
 	// EpollInstance.ReadEvents() rechecks their readiness.
-	epi.Callback(nil)
+	epi.Callback(nil, waiter.EventMaskFromLinux(epi.mask))
+}
+
+// beforeSave is called by stateify.
+func (fd *FileDescription) beforeSave() {
+	fd.saved = true
+	if fd.statusFlags&linux.O_ASYNC != 0 && fd.asyncHandler != nil {
+		fd.asyncHandler.Unregister(fd)
+	}
+}
+
+// afterLoad is called by stateify.
+func (fd *FileDescription) afterLoad() {
+	if fd.statusFlags&linux.O_ASYNC != 0 && fd.asyncHandler != nil {
+		fd.asyncHandler.Register(fd)
+	}
 }