memdesc: Add a MEMDESC_VMPAGES descriptor type.

This memory descriptor is backed by an array of VM pages.  This type
requires adding a new field to 'struct memdesc' to hold the offset
within the first page.  For LP64 systems, this new field is added in
an existing padding hole so does not increase the size.  For ILP32
systems, this grows 'struct memdesc' from 12 to 16 bytes.

Reviewed by:	imp, markj
Sponsored by:	Chelsio Communications
Differential Revision:	https://reviews.freebsd.org/D41028

sys/kern/subr_bus_dma.c

@@ -583,6 +583,10 @@ bus_dmamap_load_mem(bus_dma_tag_t dmat, bus_dmamap_t map,
 		error = _bus_dmamap_load_mbuf_sg(dmat, map, mem->u.md_mbuf,
 		    NULL, &nsegs, flags);
 		break;
+	case MEMDESC_VMPAGES:
+		error = _bus_dmamap_load_ma(dmat, map, mem->u.md_ma,
+		    mem->md_len, mem->md_offset, flags, NULL, &nsegs);
+		break;
 	}
 	nsegs++;
 

sys/sys/memdesc.h

@@ -35,6 +35,7 @@ struct bio;
 struct bus_dma_segment;
 struct uio;
 struct mbuf;
+struct vm_page;
 union ccb;
 
 /*
@@ -49,11 +50,15 @@ struct memdesc {
 		struct bio		*md_bio;
 		struct uio		*md_uio;
 		struct mbuf		*md_mbuf;
+		struct vm_page 		**md_ma;
 	} u;
 	union {				/* type specific data. */
-		size_t		md_len;	/* VADDR, PADDR */
+		size_t		md_len;	/* VADDR, PADDR, VMPAGES */
 		int		md_nseg; /* VLIST, PLIST */
 	};
+	union {
+		uint32_t	md_offset; /* VMPAGES */
+	};
 	uint32_t	md_type;	/* Type of memory. */
 };
 
@@ -64,6 +69,7 @@ struct memdesc {
 #define	MEMDESC_BIO	5	/* Pointer to a bio (block io). */
 #define	MEMDESC_UIO	6	/* Pointer to a uio (any io). */
 #define	MEMDESC_MBUF	7	/* Pointer to a mbuf (network io). */
+#define	MEMDESC_VMPAGES	8	/* Pointer to array of VM pages. */
 
 static inline struct memdesc
 memdesc_vaddr(void *vaddr, size_t len)
@@ -146,6 +152,19 @@ memdesc_mbuf(struct mbuf *mbuf)
 	return (mem);
 }
 
+static inline struct memdesc
+memdesc_vmpages(struct vm_page **ma, size_t len, u_int ma_offset)
+{
+	struct memdesc mem;
+
+	mem.u.md_ma = ma;
+	mem.md_len = len;
+	mem.md_type = MEMDESC_VMPAGES;
+	mem.md_offset = ma_offset;
+
+	return (mem);
+}
+
 struct memdesc	memdesc_ccb(union ccb *ccb);
 
 #endif /* _SYS_MEMDESC_H_ */