From b577e693aa898b1a01038c0c011e5ddfcff9b97f Mon Sep 17 00:00:00 2001
From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Sat, 7 Nov 2015 00:18:14 +0000
Subject: [PATCH] fd: implement kern.proc.nfds sysctl

Intended purpose is to provide an equivalent of OpenBSD's getdtablecount
syscall for the compat library..
---
 sys/kern/kern_descrip.c | 24 ++++++++++++++++++++++++
 sys/sys/sysctl.h        |  1 +
 2 files changed, 25 insertions(+)

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index 23b7d5489e53..a74d27f62040 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -3157,6 +3157,30 @@ filedesc_to_leader_alloc(struct filedesc_to_leader *old, struct filedesc *fdp, s
 	return (fdtol);
 }
 
+static int
+sysctl_kern_proc_nfds(SYSCTL_HANDLER_ARGS)
+{
+	struct filedesc *fdp;
+	int i, count, slots;
+
+	if (*(int *)arg1 != 0)
+		return (EINVAL);
+
+	fdp = curproc->p_fd;
+	count = 0;
+	FILEDESC_SLOCK(fdp);
+	slots = NDSLOTS(fdp->fd_lastfile + 1);
+	for (i = 0; i < slots; i++)
+		count += bitcountl(fdp->fd_map[i]);
+	FILEDESC_SUNLOCK(fdp);
+
+	return (SYSCTL_OUT(req, &count, sizeof(count)));
+}
+
+static SYSCTL_NODE(_kern_proc, KERN_PROC_NFDS, nfds,
+    CTLFLAG_RD|CTLFLAG_MPSAFE, sysctl_kern_proc_nfds,
+    "Number of open file descriptors");
+
 /*
  * Get file structures globally.
  */
diff --git a/sys/sys/sysctl.h b/sys/sys/sysctl.h
index 4e6c556736d6..206bfcf9483b 100644
--- a/sys/sys/sysctl.h
+++ b/sys/sys/sysctl.h
@@ -703,6 +703,7 @@ TAILQ_HEAD(sysctl_ctx_list, sysctl_ctx_entry);
 #define	KERN_PROC_OSREL		40	/* osreldate for process binary */
 #define	KERN_PROC_SIGTRAMP	41	/* signal trampoline location */
 #define	KERN_PROC_CWD		42	/* process current working directory */
+#define	KERN_PROC_NFDS		43	/* number of open file descriptors */
 
 /*
  * KERN_IPC identifiers