Changes missing in last submit

Updates #1487
Updates #1623

PiperOrigin-RevId: 292040835

pkg/sentry/kernel/fd_table.go

@@ -15,9 +15,9 @@
 package kernel
 
 import (
-	"bytes"
 	"fmt"
 	"math"
+	"strings"
 	"sync/atomic"
 	"syscall"
 
@@ -221,24 +221,24 @@ func (f *FDTable) forEach(fn func(fd int32, file *fs.File, fileVFS2 *vfs.FileDes
 
 // String is a stringer for FDTable.
 func (f *FDTable) String() string {
-	var b bytes.Buffer
+	var buf strings.Builder
 	f.forEach(func(fd int32, file *fs.File, fileVFS2 *vfs.FileDescription, flags FDFlags) {
 		switch {
 		case file != nil:
 			n, _ := file.Dirent.FullName(nil /* root */)
-			b.WriteString(fmt.Sprintf("\tfd:%d => name %s\n", fd, n))
+			fmt.Fprintf(&buf, "\tfd:%d => name %s\n", fd, n)
 
 		case fileVFS2 != nil:
-			fs := fileVFS2.VirtualDentry().Mount().Filesystem().VirtualFilesystem()
-			// TODO(gvisor.dev/issue/1623): We have no context nor root. Will this work?
-			name, err := fs.PathnameWithDeleted(context.Background(), vfs.VirtualDentry{}, fileVFS2.VirtualDentry())
+			vfsObj := fileVFS2.Mount().Filesystem().VirtualFilesystem()
+			name, err := vfsObj.PathnameWithDeleted(context.Background(), vfs.VirtualDentry{}, fileVFS2.VirtualDentry())
 			if err != nil {
-				b.WriteString(fmt.Sprintf("<err: %v>\n", err))
+				fmt.Fprintf(&buf, "<err: %v>\n", err)
+				return
 			}
-			b.WriteString(fmt.Sprintf("\tfd:%d => name %s\n", fd, name))
+			fmt.Fprintf(&buf, "\tfd:%d => name %s\n", fd, name)
 		}
 	})
-	return b.String()
+	return buf.String()
 }
 
 // NewFDs allocates new FDs guaranteed to be the lowest number available

pkg/sentry/syscalls/linux/sys_read.go

@@ -29,7 +29,7 @@ import (
 )
 
 const (
-	// EventMaskRead contains events that can be triggerd on reads.
+	// EventMaskRead contains events that can be triggered on reads.
 	EventMaskRead = waiter.EventIn | waiter.EventHUp | waiter.EventErr
 )
 

pkg/sentry/syscalls/linux/vfs2/sys_read.go

@@ -24,6 +24,11 @@ import (
 	"gvisor.dev/gvisor/pkg/waiter"
 )
 
+const (
+	// EventMaskRead contains events that can be triggered on reads.
+	EventMaskRead = waiter.EventIn | waiter.EventHUp | waiter.EventErr
+)
+
 // Read implements linux syscall read(2).  Note that we try to get a buffer that
 // is exactly the size requested because some applications like qemu expect
 // they can do large reads all at once.  Bug for bug.  Same for other read
@@ -39,11 +44,6 @@ func Read(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallC
 	}
 	defer file.DecRef()
 
-	// Check that the file is readable.
-	if !file.IsReadable() {
-		return 0, nil, syserror.EBADF
-	}
-
 	// Check that the size is legitimate.
 	si := int(size)
 	if si < 0 {
@@ -70,8 +70,8 @@ func read(t *kernel.Task, file *vfs.FileDescription, dst usermem.IOSequence, opt
 	}
 
 	// Register for notifications.
-	_, ch := waiter.NewChannelEntry(nil)
-	// file.EventRegister(&w, EventMaskRead)
+	w, ch := waiter.NewChannelEntry(nil)
+	file.EventRegister(&w, EventMaskRead)
 
 	total := n
 	for {
@@ -89,7 +89,7 @@ func read(t *kernel.Task, file *vfs.FileDescription, dst usermem.IOSequence, opt
 			break
 		}
 	}
-	//file.EventUnregister(&w)
+	file.EventUnregister(&w)
 
 	return total, err
 }