BPF BIOCSETF

[Matthew Luckie]

BIOCSETF and BIOCSETWF call reset_d which discards any packets
currently in the hold buffer and resets the packet rx count.

The patch below adds BIOCSETFNR, an ioctl that swaps the BPF filter
without resetting the hold buffer and without resetting the packet rx
counts, which is handy when the application wants to adjust its filter
program but without discarding whatever the system might have
buffered.

I've also changed BIOCSETWF to map to the new function.  I don't see
the rationale in having BIOCSETWF mucking with the receive stats and
hold buffer.

Patch below is against RELENG_6.  I'll send a PR tomorrow against HEAD
if there aren't any comments or complaints; the main difference will
be the extra cruft to make bpf_jitter work.

Thoughts?

Matthew

--- bpf.c.orig	Mon Nov 19 14:23:52 2007
+++ bpf.c	Mon Nov 19 15:55:05 2007
@@ -103,7 +103,8 @@
 		    u_int, void (*)(const void *, void *, size_t),
 		    struct timeval *);
 static void	reset_d(struct bpf_d *);
-static int	 bpf_setf(struct bpf_d *, struct bpf_program *, u_long cmd);
+static int	bpf_setf(struct bpf_d *, struct bpf_program *);
+static int	bpf_setfnr(struct bpf_d *, struct bpf_program *, u_long);
 static int	bpf_getdltlist(struct bpf_d *, struct bpf_dltlist *);
 static int	bpf_setdlt(struct bpf_d *, u_int);
 static void	filt_bpfdetach(struct knote *);
@@ -755,8 +756,12 @@
 	 * Set link layer read filter.
 	 */
 	case BIOCSETF:
+		error = bpf_setf(d, (struct bpf_program *)addr);
+		break;
+
+	case BIOCSETFNR:
 	case BIOCSETWF:
-		error = bpf_setf(d, (struct bpf_program *)addr, cmd);
+		error = bpf_setfnr(d, (struct bpf_program *)addr, cmd);
 		break;
 
 	/*
@@ -976,26 +981,17 @@
  * free it and replace it.  Returns EINVAL for bogus requests.
  */
 static int
-bpf_setf(struct bpf_d *d, struct bpf_program *fp, u_long cmd)
+bpf_setf(struct bpf_d *d, struct bpf_program *fp)
 {
 	struct bpf_insn *fcode, *old;
-	u_int wfilter, flen, size;
+	u_int flen, size;
 
-	if (cmd == BIOCSETWF) {
-		old = d->bd_wfilter;
-		wfilter = 1;
-	} else {
-		wfilter = 0;
-		old = d->bd_rfilter;
-	}
 	if (fp->bf_insns == NULL) {
 		if (fp->bf_len != 0)
 			return (EINVAL);
 		BPFD_LOCK(d);
-		if (wfilter)
-			d->bd_wfilter = NULL;
-		else
-			d->bd_rfilter = NULL;
+		old = d->bd_rfilter;
+		d->bd_rfilter = NULL;
 		reset_d(d);
 		BPFD_UNLOCK(d);
 		if (old != NULL)
@@ -1011,10 +1007,8 @@
 	if (copyin((caddr_t)fp->bf_insns, (caddr_t)fcode, size) == 0 &&
 	    bpf_validate(fcode, (int)flen)) {
 		BPFD_LOCK(d);
-		if (wfilter)
-			d->bd_wfilter = fcode;
-		else
-			d->bd_rfilter = fcode;
+		old = d->bd_rfilter;
+		d->bd_rfilter = fcode;
 		reset_d(d);
 		BPFD_UNLOCK(d);
 		if (old != NULL)
@@ -1024,6 +1018,50 @@
 	}
 	free((caddr_t)fcode, M_BPF);
 	return (EINVAL);
+}
+
+/*
+ * Set d's packet filter program to fp.  If this file already has a filter,
+ * replace it but keep any existing buffered packets.
+ */
+static int
+bpf_setfnr(struct bpf_d *d, struct bpf_program *fp, u_long cmd)
+{
+	struct bpf_insn *fcode, *old;
+	u_int flen, size;
+
+	if (fp->bf_insns != NULL) {
+		flen = fp->bf_len;
+		if (flen > bpf_maxinsns)
+			return (EINVAL);
+
+		size = flen * sizeof(*fp->bf_insns);
+		fcode = (struct bpf_insn *)malloc(size, M_BPF, M_WAITOK);
+		if (copyin((caddr_t)fp->bf_insns, (caddr_t)fcode, size) != 0 ||
+		    bpf_validate(fcode, (int)flen) == 0) {
+			free((caddr_t)fcode, M_BPF);
+			return (EINVAL);
+		}
+	} else {
+		if (fp->bf_len != 0)
+			return (EINVAL);
+		fcode = NULL;
+	}
+
+	BPFD_LOCK(d);
+	if (cmd == BIOCSETFNR) {
+		old = d->bd_rfilter;
+		d->bd_rfilter = fcode;
+	} else {
+		old = d->bd_wfilter;
+		d->bd_wfilter = fcode;
+	}
+	BPFD_UNLOCK(d);
+
+	if(old != NULL)
+		free((caddr_t)old, M_BPF);
+
+	return (0);
 }
 
 /*
--- bpf.h.orig	Mon Nov 19 14:24:11 2007
+++ bpf.h	Mon Nov 19 14:25:16 2007
@@ -115,6 +115,7 @@
 #define	BIOCGDLTLIST	_IOWR('B',121, struct bpf_dltlist)
 #define	BIOCLOCK	_IO('B', 122)
 #define	BIOCSETWF	_IOW('B',123, struct bpf_program)
+#define BIOCSETFNR	_IOW('B',124, struct bpf_program)
 
 /*
  * Structure prepended to each packet.