Consistent precondition formatting

Our "Preconditions:" blocks are very useful to determine the input invariants,
but they are bit inconsistent throughout the codebase, which makes them harder
to read (particularly cases with 5+ conditions in a single paragraph).

I've reformatted all of the cases to fit in simple rules:

1. Cases with a single condition are placed on a single line.
2. Cases with multiple conditions are placed in a bulleted list.

This format has been added to the style guide.

I've also mentioned "Postconditions:", though those are much less frequently
used, and all uses already match this style.

PiperOrigin-RevId: 327687465

pkg/sentry/fsimpl/tmpfs/directory.go

@@ -57,8 +57,9 @@ func (fs *filesystem) newDirectory(kuid auth.KUID, kgid auth.KGID, mode linux.Fi
 	return dir
 }
 
-// Preconditions: filesystem.mu must be locked for writing. dir must not
-// already contain a child with the given name.
+// Preconditions:
+// * filesystem.mu must be locked for writing.
+// * dir must not already contain a child with the given name.
 func (dir *directory) insertChildLocked(child *dentry, name string) {
 	child.parent = &dir.dentry
 	child.name = name

pkg/sentry/fsimpl/tmpfs/filesystem.go

@@ -39,7 +39,9 @@ func (fs *filesystem) Sync(ctx context.Context) error {
 //
 // stepLocked is loosely analogous to fs/namei.c:walk_component().
 //
-// Preconditions: filesystem.mu must be locked. !rp.Done().
+// Preconditions:
+// * filesystem.mu must be locked.
+// * !rp.Done().
 func stepLocked(ctx context.Context, rp *vfs.ResolvingPath, d *dentry) (*dentry, error) {
 	dir, ok := d.inode.impl.(*directory)
 	if !ok {
@@ -97,7 +99,9 @@ afterSymlink:
 // walkParentDirLocked is loosely analogous to Linux's
 // fs/namei.c:path_parentat().
 //
-// Preconditions: filesystem.mu must be locked. !rp.Done().
+// Preconditions:
+// * filesystem.mu must be locked.
+// * !rp.Done().
 func walkParentDirLocked(ctx context.Context, rp *vfs.ResolvingPath, d *dentry) (*directory, error) {
 	for !rp.Final() {
 		next, err := stepLocked(ctx, rp, d)
@@ -139,8 +143,9 @@ func resolveLocked(ctx context.Context, rp *vfs.ResolvingPath) (*dentry, error)
 // doCreateAt is loosely analogous to a conjunction of Linux's
 // fs/namei.c:filename_create() and done_path_create().
 //
-// Preconditions: !rp.Done(). For the final path component in rp,
-// !rp.ShouldFollowSymlink().
+// Preconditions:
+// * !rp.Done().
+// * For the final path component in rp, !rp.ShouldFollowSymlink().
 func (fs *filesystem) doCreateAt(ctx context.Context, rp *vfs.ResolvingPath, dir bool, create func(parentDir *directory, name string) error) error {
 	fs.mu.Lock()
 	defer fs.mu.Unlock()

pkg/sentry/fsimpl/tmpfs/named_pipe.go

@@ -28,8 +28,8 @@ type namedPipe struct {
 }
 
 // Preconditions:
-//   * fs.mu must be locked.
-//   * rp.Mount().CheckBeginWrite() has been called successfully.
+// * fs.mu must be locked.
+// * rp.Mount().CheckBeginWrite() has been called successfully.
 func (fs *filesystem) newNamedPipe(kuid auth.KUID, kgid auth.KGID, mode linux.FileMode) *inode {
 	file := &namedPipe{pipe: pipe.NewVFSPipe(true /* isNamed */, pipe.DefaultPipeSize, usermem.PageSize)}
 	file.inode.init(file, fs, kuid, kgid, linux.S_IFIFO|mode)

pkg/sentry/fsimpl/tmpfs/tmpfs.go

@@ -340,8 +340,10 @@ func (i *inode) init(impl interface{}, fs *filesystem, kuid auth.KUID, kgid auth
 
 // incLinksLocked increments i's link count.
 //
-// Preconditions: filesystem.mu must be locked for writing. i.nlink != 0.
-// i.nlink < maxLinks.
+// Preconditions:
+// * filesystem.mu must be locked for writing.
+// * i.nlink != 0.
+// * i.nlink < maxLinks.
 func (i *inode) incLinksLocked() {
 	if i.nlink == 0 {
 		panic("tmpfs.inode.incLinksLocked() called with no existing links")
@@ -355,7 +357,9 @@ func (i *inode) incLinksLocked() {
 // decLinksLocked decrements i's link count. If the link count reaches 0, we
 // remove a reference on i as well.
 //
-// Preconditions: filesystem.mu must be locked for writing. i.nlink != 0.
+// Preconditions:
+// * filesystem.mu must be locked for writing.
+// * i.nlink != 0.
 func (i *inode) decLinksLocked(ctx context.Context) {
 	if i.nlink == 0 {
 		panic("tmpfs.inode.decLinksLocked() called with no existing links")
@@ -594,8 +598,9 @@ func (i *inode) touchCMtime() {
 	i.mu.Unlock()
 }
 
-// Preconditions: The caller has called vfs.Mount.CheckBeginWrite() and holds
-// inode.mu.
+// Preconditions:
+// * The caller has called vfs.Mount.CheckBeginWrite().
+// * inode.mu must be locked.
 func (i *inode) touchCMtimeLocked() {
 	now := i.fs.clock.Now().Nanoseconds()
 	atomic.StoreInt64(&i.mtime, now)