Add plumbing for importing fds in VFS2, along with non-socket, non-TTY impl.

In VFS2, imported file descriptors are stored in a kernfs-based filesystem.
Upon calling ImportFD, the host fd can be accessed in two ways:
1. a FileDescription that can be added to the FDTable, and
2. a Dentry in the host.filesystem mount, which we will want to access through
magic symlinks in /proc/[pid]/fd/.

An implementation of the kernfs.Inode interface stores a unique host fd. This
inode can be inserted into file descriptions as well as dentries.

This change also plumbs in three FileDescriptionImpls corresponding to fds for
sockets, TTYs, and other files (only the latter is implemented here).
These implementations will mostly make corresponding syscalls to the host.
Where possible, the logic is ported over from pkg/sentry/fs/host.

Updates #1672

PiperOrigin-RevId: 299417263

1 files changed, 8 insertions, 4 deletions

diff --git a/pkg/sentry/fs/host/util.go b/pkg/sentry/fs/host/util.go
index e37e687c6..7c60dc1db 100644
--- a/pkg/sentry/fs/host/util.go
+++ b/pkg/sentry/fs/host/util.go
@@ -24,7 +24,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/device"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
-	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/time"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
@@ -152,9 +152,9 @@ func unstableAttr(mo *superOperations, s *syscall.Stat_t) fs.UnstableAttr {
 		Usage:            s.Blocks * 512,
 		Perms:            fs.FilePermsFromMode(linux.FileMode(s.Mode)),
 		Owner:            owner(mo, s),
-		AccessTime:       ktime.FromUnix(s.Atim.Sec, s.Atim.Nsec),
-		ModificationTime: ktime.FromUnix(s.Mtim.Sec, s.Mtim.Nsec),
-		StatusChangeTime: ktime.FromUnix(s.Ctim.Sec, s.Ctim.Nsec),
+		AccessTime:       time.FromUnix(s.Atim.Sec, s.Atim.Nsec),
+		ModificationTime: time.FromUnix(s.Mtim.Sec, s.Mtim.Nsec),
+		StatusChangeTime: time.FromUnix(s.Ctim.Sec, s.Ctim.Nsec),
 		Links:            uint64(s.Nlink),
 	}
 }
@@ -165,6 +165,8 @@ type dirInfo struct {
 	bufp int    // location of next record in buf.
 }
 
+// LINT.IfChange
+
 // isBlockError unwraps os errors and checks if they are caused by EAGAIN or
 // EWOULDBLOCK. This is so they can be transformed into syserror.ErrWouldBlock.
 func isBlockError(err error) bool {
@@ -177,6 +179,8 @@ func isBlockError(err error) bool {
 	return false
 }
 
+// LINT.ThenChange(../../fsimpl/host/util.go)
+
 func hostEffectiveKIDs() (uint32, []uint32, error) {
 	gids, err := os.Getgroups()
 	if err != nil {