proc: show file flags in fdinfo

Currently, there is an attempt to print FD flags, but
they are not decoded into a number, so we see something like this:

/criu # cat /proc/self/fdinfo/0
flags: {%!o(bool=000false)}

Actually, fdinfo has to contain file flags.

Change-Id: Idcbb7db908067447eb9ae6f2c3cfb861f2be1a97
PiperOrigin-RevId: 206794498

2 files changed, 51 insertions, 9 deletions

diff --git a/pkg/sentry/fs/flags.go b/pkg/sentry/fs/flags.go
index 810452584..da0ff58af 100644
--- a/pkg/sentry/fs/flags.go
+++ b/pkg/sentry/fs/flags.go
@@ -14,6 +14,10 @@
 
 package fs
 
+import (
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+)
+
 // FileFlags encodes file flags.
 type FileFlags struct {
 	// Direct indicates that I/O should be done directly.
@@ -78,3 +82,38 @@ func (f FileFlags) Settable() SettableFileFlags {
 		Async:       f.Async,
 	}
 }
+
+// ToLinux converts a FileFlags object to a Linux representation.
+func (f FileFlags) ToLinux() (mask uint) {
+	if f.Direct {
+		mask |= linux.O_DIRECT
+	}
+	if f.NonBlocking {
+		mask |= linux.O_NONBLOCK
+	}
+	if f.Sync {
+		mask |= linux.O_SYNC
+	}
+	if f.Append {
+		mask |= linux.O_APPEND
+	}
+	if f.Directory {
+		mask |= linux.O_DIRECTORY
+	}
+	if f.Async {
+		mask |= linux.O_ASYNC
+	}
+	if f.LargeFile {
+		mask |= linux.O_LARGEFILE
+	}
+
+	switch {
+	case f.Read && f.Write:
+		mask |= linux.O_RDWR
+	case f.Write:
+		mask |= linux.O_WRONLY
+	case f.Read:
+		mask |= linux.O_RDONLY
+	}
+	return
+}
diff --git a/pkg/sentry/fs/proc/fds.go b/pkg/sentry/fs/proc/fds.go
index 2eca9ac31..194a9c12a 100644
--- a/pkg/sentry/fs/proc/fds.go
+++ b/pkg/sentry/fs/proc/fds.go
@@ -40,16 +40,16 @@ func walkDescriptors(t *kernel.Task, p string, toInode func(*fs.File, kernel.FDF
 	}
 
 	var file *fs.File
-	var flags kernel.FDFlags
+	var fdFlags kernel.FDFlags
 	t.WithMuLocked(func(t *kernel.Task) {
 		if fdm := t.FDMap(); fdm != nil {
-			file, flags = fdm.GetDescriptor(kdefs.FD(n))
+			file, fdFlags = fdm.GetDescriptor(kdefs.FD(n))
 		}
 	})
 	if file == nil {
 		return nil, syserror.ENOENT
 	}
-	return toInode(file, flags), nil
+	return toInode(file, fdFlags), nil
 }
 
 // readDescriptors reads fds in the task starting at offset, and calls the
@@ -200,17 +200,20 @@ func (f *fdDir) DeprecatedReaddir(ctx context.Context, dirCtx *fs.DirCtx, offset
 type fdInfo struct {
 	ramfs.File
 
-	flags kernel.FDFlags
+	flags   fs.FileFlags
+	fdFlags kernel.FDFlags
 }
 
 // newFdInfo returns a new fdInfo based on an existing file.
-func newFdInfo(t *kernel.Task, _ *fs.File, flags kernel.FDFlags, msrc *fs.MountSource) *fs.Inode {
-	fdi := &fdInfo{flags: flags}
+func newFdInfo(t *kernel.Task, file *fs.File, fdFlags kernel.FDFlags, msrc *fs.MountSource) *fs.Inode {
+	fdi := &fdInfo{flags: file.Flags(), fdFlags: fdFlags}
 	fdi.InitFile(t, fs.RootOwner, fs.FilePermissions{User: fs.PermMask{Read: true}})
 	// TODO: Get pos, locks, and other data.  For now we only
 	// have flags.
 	// See https://www.kernel.org/doc/Documentation/filesystems/proc.txt
-	fdi.Append([]byte(fmt.Sprintf("flags: %08o\n", flags)))
+
+	flags := file.Flags().ToLinux() | fdFlags.ToLinuxFileFlags()
+	fdi.Append([]byte(fmt.Sprintf("flags:\t0%o\n", flags)))
 	return newFile(fdi, msrc, fs.SpecialFile, t)
 }
 
@@ -241,8 +244,8 @@ func newFdInfoDir(t *kernel.Task, msrc *fs.MountSource) *fs.Inode {
 
 // Lookup loads an fd in /proc/TID/fdinfo into a Dirent.
 func (fdid *fdInfoDir) Lookup(ctx context.Context, dir *fs.Inode, p string) (*fs.Dirent, error) {
-	n, err := walkDescriptors(fdid.t, p, func(file *fs.File, flags kernel.FDFlags) *fs.Inode {
-		return newFdInfo(fdid.t, file, flags, dir.MountSource)
+	n, err := walkDescriptors(fdid.t, p, func(file *fs.File, fdFlags kernel.FDFlags) *fs.Inode {
+		return newFdInfo(fdid.t, file, fdFlags, dir.MountSource)
 	})
 	if err != nil {
 		return nil, err