Implement waiter.Waitable methods on VFS2 host inodes.

This fixes bash in Ubuntu.

Updates #1672.

PiperOrigin-RevId: 309298252

pkg/sentry/fsimpl/host/host.go

@@ -24,6 +24,7 @@ import (
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/fdnotifier"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
@@ -35,6 +36,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/pkg/waiter"
 )
 
 // filesystemType implements vfs.FilesystemType.
@@ -88,11 +90,12 @@ func ImportFD(ctx context.Context, mnt *vfs.Mount, hostFD int, isTTY bool) (*vfs
 	seekable := err != syserror.ESPIPE
 
 	i := &inode{
-		hostFD:   hostFD,
-		seekable: seekable,
-		isTTY:    isTTY,
-		canMap:   canMap(uint32(fileType)),
-		ino:      fs.NextIno(),
+		hostFD:     hostFD,
+		seekable:   seekable,
+		isTTY:      isTTY,
+		canMap:     canMap(uint32(fileType)),
+		wouldBlock: wouldBlock(uint32(fileType)),
+		ino:        fs.NextIno(),
 		// For simplicity, set offset to 0. Technically, we should use the existing
 		// offset on the host if the file is seekable.
 		offset: 0,
@@ -103,6 +106,17 @@ func ImportFD(ctx context.Context, mnt *vfs.Mount, hostFD int, isTTY bool) (*vfs
 		panic("files that can return EWOULDBLOCK (sockets, pipes, etc.) cannot be memory mapped")
 	}
 
+	// If the hostFD would block, we must set it to non-blocking and handle
+	// blocking behavior in the sentry.
+	if i.wouldBlock {
+		if err := syscall.SetNonblock(i.hostFD, true); err != nil {
+			return nil, err
+		}
+		if err := fdnotifier.AddFD(int32(i.hostFD), &i.queue); err != nil {
+			return nil, err
+		}
+	}
+
 	d := &kernfs.Dentry{}
 	d.Init(i)
 	// i.open will take a reference on d.
@@ -125,6 +139,12 @@ type inode struct {
 	// This field is initialized at creation time and is immutable.
 	hostFD int
 
+	// wouldBlock is true if the host FD would return EWOULDBLOCK for
+	// operations that would block.
+	//
+	// This field is initialized at creation time and is immutable.
+	wouldBlock bool
+
 	// seekable is false if the host fd points to a file representing a stream,
 	// e.g. a socket or a pipe. Such files are not seekable and can return
 	// EWOULDBLOCK for I/O operations.
@@ -152,6 +172,9 @@ type inode struct {
 
 	// offset specifies the current file offset.
 	offset int64
+
+	// Event queue for blocking operations.
+	queue waiter.Queue
 }
 
 // Note that these flags may become out of date, since they can be modified
@@ -354,6 +377,9 @@ func (i *inode) DecRef() {
 
 // Destroy implements kernfs.Inode.
 func (i *inode) Destroy() {
+	if i.wouldBlock {
+		fdnotifier.RemoveFD(int32(i.hostFD))
+	}
 	if err := unix.Close(i.hostFD); err != nil {
 		log.Warningf("failed to close host fd %d: %v", i.hostFD, err)
 	}
@@ -614,3 +640,20 @@ func (f *fileDescription) ConfigureMMap(_ context.Context, opts *memmap.MMapOpts
 	// TODO(gvisor.dev/issue/1672): Implement ConfigureMMap and Mappable interface.
 	return syserror.ENODEV
 }
+
+// EventRegister implements waiter.Waitable.EventRegister.
+func (f *fileDescription) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
+	f.inode.queue.EventRegister(e, mask)
+	fdnotifier.UpdateFD(int32(f.inode.hostFD))
+}
+
+// EventUnregister implements waiter.Waitable.EventUnregister.
+func (f *fileDescription) EventUnregister(e *waiter.Entry) {
+	f.inode.queue.EventUnregister(e)
+	fdnotifier.UpdateFD(int32(f.inode.hostFD))
+}
+
+// Readiness uses the poll() syscall to check the status of the underlying FD.
+func (f *fileDescription) Readiness(mask waiter.EventMask) waiter.EventMask {
+	return fdnotifier.NonBlockingPoll(int32(f.inode.hostFD), mask)
+}