Add a call to synthesize a C/H/S value for block emulations

that require it (ahci). The algorithm used is from the VHD
specification.

2 files changed, 51 insertions, 0 deletions

diff --git a/usr.sbin/bhyve/block_if.c b/usr.sbin/bhyve/block_if.c
index b29bc7856e86..1ec0344f3fca 100644
--- a/usr.sbin/bhyve/block_if.c
+++ b/usr.sbin/bhyve/block_if.c
@@ -390,6 +390,55 @@ blockif_close(struct blockif_ctxt *bc)
 }
 
 /*
+ * Return virtual C/H/S values for a given block. Use the algorithm
+ * outlined in the VHD specification to calculate values.
+ */
+void
+blockif_chs(struct blockif_ctxt *bc, uint16_t *c, uint8_t *h, uint8_t *s)
+{
+	off_t sectors;		/* total sectors of the block dev */
+	off_t hcyl;		/* cylinders times heads */
+	uint16_t secpt;		/* sectors per track */
+	uint8_t heads;
+
+	assert(bc->bc_magic == BLOCKIF_SIG);
+
+	sectors = bc->bc_size / bc->bc_sectsz;
+
+	/* Clamp the size to the largest possible with CHS */
+	if (sectors > 65535UL*16*255)
+		sectors = 65535UL*16*255;
+
+	if (sectors >= 65536UL*16*63) {
+		secpt = 255;
+		heads = 16;
+		hcyl = sectors / secpt;
+	} else {
+		secpt = 17;
+		hcyl = sectors / secpt;
+		heads = (hcyl + 1023) / 1024;
+
+		if (heads < 4)
+			heads = 4;
+
+		if (hcyl >= (heads * 1024) || heads > 16) {
+			secpt = 31;
+			heads = 16;
+			hcyl = sectors / secpt;
+		}
+		if (hcyl >= (heads * 1024)) {
+			secpt = 63;
+			heads = 16;
+			hcyl = sectors / secpt;
+		}
+	}
+
+	*c = hcyl / heads;
+	*h = heads;
+	*s = secpt;
+}
+
+/*
  * Accessors
  */
 off_t
diff --git a/usr.sbin/bhyve/block_if.h b/usr.sbin/bhyve/block_if.h
index e0c0bb1f8c8b..c2c21f657446 100644
--- a/usr.sbin/bhyve/block_if.h
+++ b/usr.sbin/bhyve/block_if.h
@@ -52,6 +52,8 @@ struct blockif_req {
 struct blockif_ctxt;
 struct blockif_ctxt *blockif_open(const char *optstr, const char *ident);
 off_t	blockif_size(struct blockif_ctxt *bc);
+void	blockif_chs(struct blockif_ctxt *bc, uint16_t *c, uint8_t *h,
+    uint8_t *s);
 int	blockif_sectsz(struct blockif_ctxt *bc);
 int	blockif_queuesz(struct blockif_ctxt *bc);
 int	blockif_is_ro(struct blockif_ctxt *bc);