diff --git a/lib/libc/sys/fcntl.2 b/lib/libc/sys/fcntl.2
--- a/lib/libc/sys/fcntl.2
+++ b/lib/libc/sys/fcntl.2
@@ -28,7 +28,7 @@
 .\"     @(#)fcntl.2	8.2 (Berkeley) 1/12/94
 .\" $FreeBSD$
 .\"
-.Dd January 6, 2021
+.Dd December 7, 2021
 .Dt FCNTL 2
 .Os
 .Sh NAME
@@ -53,7 +53,7 @@
 .Fa cmd ,
 .Fn fcntl
 can take an additional third argument
-.Fa "int arg" .
+.Fa "long arg" .
 .Bl -tag -width F_DUP2FD_CLOEXEC
 .It Dv F_DUPFD
 Return a new descriptor as follows:
@@ -190,6 +190,14 @@
 .Xr mount 2
 or unionfs).
 This is a hack not intended to be used outside of libc.
+.It Dv F_KINFO
+Fills
+.Vt struct kinfo_file
+for the file referenced by the specified file descriptor.
+The
+.Fa arg
+argument should point to the storage for
+.Vt struct kinfo_file .
 .El
 .Pp
 The flags for the
diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -477,6 +477,7 @@
 	struct proc *p;
 	struct vnode *vp;
 	struct mount *mp;
+	struct kinfo_file *kif;
 	int error, flg, seals, tmp;
 	uint64_t bsize;
 	off_t foffset;
@@ -852,6 +853,20 @@
 		fdrop(fp, td);
 		break;
 
+	case F_KINFO:
+		kif = malloc(sizeof(*kif), M_TEMP, M_WAITOK);
+		error = fget_unlocked(fdp, fd, &cap_no_rights, &fp);
+		if (error == 0) {
+			error = fo_fill_kinfo(fp, kif, fdp);
+			if (error == 0) {
+				error = copyout(kif, (void *)arg,
+				    sizeof(*kif));
+			}
+			fdrop(fp, td);
+		}
+		free(kif, M_TEMP);
+		break;
+
 	default:
 		error = EINVAL;
 		break;
diff --git a/sys/sys/fcntl.h b/sys/sys/fcntl.h
--- a/sys/sys/fcntl.h
+++ b/sys/sys/fcntl.h
@@ -270,6 +270,7 @@
 #define	F_ADD_SEALS	19
 #define	F_GET_SEALS	20
 #define	F_ISUNIONSTACK	21		/* Kludge for libc, don't use it. */
+#define	F_KINFO		22		/* Return kinfo_file for this fd */
 
 /* Seals (F_ADD_SEALS, F_GET_SEALS). */
 #define	F_SEAL_SEAL	0x0001		/* Prevent adding sealings */