socket: add Conn.Pidfd* wrappers

Signed-off-by: Matt Layher <mdlayher@gmail.com>

conn.go

@@ -184,7 +184,7 @@ func socket(domain, typ, proto int, name string) (*Conn, error) {
 			}
 
 			// No error, prepare the Conn.
-			return newConn(fd, name)
+			return New(fd, name)
 		case !ready(err):
 			// System call interrupted or not ready, try again.
 			continue
@@ -211,7 +211,7 @@ func socket(domain, typ, proto int, name string) (*Conn, error) {
 			unix.CloseOnExec(fd)
 			syscall.ForkLock.RUnlock()
 
-			return newConn(fd, name)
+			return New(fd, name)
 		default:
 			// Unhandled error.
 			return nil, os.NewSyscallError("socket", err)
@@ -230,7 +230,7 @@ func FileConn(f *os.File, name string) (*Conn, error) {
 	switch err {
 	case nil:
 		// OK, ready to set up non-blocking I/O.
-		return newConn(fd, name)
+		return New(fd, name)
 	case unix.EINVAL:
 		// The kernel rejected our fcntl(2), fall back to separate dup(2) and
 		// setting close on exec.
@@ -248,18 +248,25 @@ func FileConn(f *os.File, name string) (*Conn, error) {
 		unix.CloseOnExec(fd)
 		syscall.ForkLock.RUnlock()
 
-		return newConn(fd, name)
+		return New(fd, name)
 	default:
 		// Any other errors.
 		return nil, os.NewSyscallError("fcntl", err)
 	}
 }
 
-// TODO(mdlayher): consider exporting newConn as New?
-
-// newConn wraps an existing file descriptor to create a Conn. name should be a
+// New wraps an existing file descriptor to create a Conn. name should be a
 // unique name for the socket type such as "netlink" or "vsock".
-func newConn(fd int, name string) (*Conn, error) {
+//
+// Most callers should use Socket or FileConn to construct a Conn. New is
+// intended for integrating with specific system calls which provide a file
+// descriptor that supports asynchronous I/O. The file descriptor is immediately
+// set to nonblocking mode and registered with Go's runtime network poller for
+// future I/O operations.
+//
+// Unlike FileConn, New does not duplicate the existing file descriptor in any
+// way. The returned Conn takes ownership of the underlying file descriptor.
+func New(fd int, name string) (*Conn, error) {
 	// All Conn I/O is nonblocking for integration with Go's runtime network
 	// poller. Depending on the OS this might already be set but it can't hurt
 	// to set it again.
@@ -318,7 +325,7 @@ func (c *Conn) Accept(flags int) (*Conn, unix.Sockaddr, error) {
 
 	// Successfully accepted a connection, wrap it in a Conn for use by the
 	// caller.
-	ac, err := newConn(nfd, c.name)
+	ac, err := New(nfd, c.name)
 	if err != nil {
 		return nil, nil, err
 	}

conn_linux.go

@@ -33,7 +33,7 @@ func (c *Conn) IoctlKCMClone() (*Conn, error) {
 	}
 
 	// Successful clone, wrap in a Conn for use by the caller.
-	return newConn(int(info.Fd), c.name)
+	return New(int(info.Fd), c.name)
 }
 
 // IoctlKCMAttach wraps ioctl(2) for unix.KCMAttach values.
@@ -50,6 +50,39 @@ func (c *Conn) IoctlKCMUnattach(info unix.KCMUnattach) error {
 	})
 }
 
+// PidfdGetfd wraps pidfd_getfd(2) for a Conn which wraps a pidfd, but returns a
+// Conn rather than a raw file descriptor.
+func (c *Conn) PidfdGetfd(targetFD, flags int) (*Conn, error) {
+	const op = "pidfd_getfd"
+
+	var (
+		outFD int
+		err   error
+	)
+
+	doErr := c.control(op, func(fd int) error {
+		outFD, err = unix.PidfdGetfd(fd, targetFD, flags)
+		return err
+	})
+	if doErr != nil {
+		return nil, doErr
+	}
+	if err != nil {
+		return nil, os.NewSyscallError(op, err)
+	}
+
+	// Successful getfd, wrap in a Conn for use by the caller.
+	return New(outFD, c.name)
+}
+
+// PidfdSendSignal wraps pidfd_send_signal(2) for a Conn which wraps a Linux
+// pidfd.
+func (c *Conn) PidfdSendSignal(sig unix.Signal, info *unix.Siginfo, flags int) error {
+	return c.controlErr("pidfd_send_signal", func(fd int) error {
+		return unix.PidfdSendSignal(fd, sig, info, flags)
+	})
+}
+
 // SetBPF attaches an assembled BPF program to a Conn.
 func (c *Conn) SetBPF(filter []bpf.RawInstruction) error {
 	// We can't point to the first instruction in the array if no instructions

go.mod

@@ -5,7 +5,7 @@ go 1.17
 require (
 	github.com/google/go-cmp v0.5.7
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
-	golang.org/x/sys v0.0.0-20220224120231-95c6836cb0e7
+	golang.org/x/sys v0.0.0-20220319134239-a9b59b0215f8
 )
 
 // Intentional pin to an older release; we don't need new features and would

go.sum

@@ -6,8 +6,8 @@ golang.org/x/net v0.0.0-20190503192946-f4e77d36d62c/go.mod h1:t9HGtf8HONx5eT2rtn
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c h1:5KslGYwFpkhGh+Q16bwMP3cOontH8FOep7tGV86Y7SQ=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20220224120231-95c6836cb0e7 h1:BXxu8t6QN0G1uff4bzZzSkpsax8+ALqTGUtz08QrV00=
-golang.org/x/sys v0.0.0-20220224120231-95c6836cb0e7/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220319134239-a9b59b0215f8 h1:OH54vjqzRWmbJ62fjuhxy7AxFFgoHN0/DPc/UrL8cAs=
+golang.org/x/sys v0.0.0-20220319134239-a9b59b0215f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=