First cut at GEOM based multipath. This is an active/passive{/passive...}

arrangement that has no intrinsic internal knowledge of whether devices
it is given are truly multipath devices. As such, this is a simplistic
approach, but still a useful one.

The basic approach is to (at present- this will change soon) use camcontrol
to find likely identical devices and and label the trailing sector of the
first one. This label contains both a full UUID and a name. The name is
what is presented in /dev/multipath, but the UUID is used as a true
distinguishor at g_taste time, thus making sure we don't have chaos
on a shared SAN where everyone names their data multipath as "Fred".

The first of N identical devices (and N *may* be 1!) becomes the active
path until a BIO request is failed with EIO or ENXIO. When this occurs,
the active disk is ripped away and the next in a list is picked to
(retry and) continue with.

During g_taste events new disks that meet the match criteria for existing
multipath geoms get added to the tail end of the list.

Thus, this active/passive setup actually does work for devices which
go away and come back, as do (now) mpt(4) and isp(4) SAN based disks.

There is still a lot to do to improve this- like about 5 of the 12
recommendations I've received about it,  but it's been functional enough
for a while that it deserves a broader test base.

Reviewed by: pjd
Sponsored by: IronPort Systems
MFC: 2 months

1 files changed, 99 insertions, 0 deletions

diff --git a/sys/geom/multipath/g_multipath.h b/sys/geom/multipath/g_multipath.h
new file mode 100644
index 0000000..22d6157
--- /dev/null
+++ b/sys/geom/multipath/g_multipath.h
@@ -0,0 +1,99 @@
+/*-
+ * Copyright (c) 2006-2007 Matthew Jacob <mjacob@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+/*
+ * Based upon work by Pawel Jakub Dawidek <pjd@FreeBSD.org> for all of the
+ * fine geom examples, and by Poul Henning Kamp <phk@FreeBSD.org> for GEOM
+ * itself, all of which is most gratefully acknowledged.
+ */
+
+#ifndef	_G_MULTIPATH_H_
+#define	_G_MULTIPATH_H_
+
+#define	G_MULTIPATH_CLASS_NAME	"MULTIPATH"
+#define	G_MULTIPATH_VERSION	1
+#define	G_MULTIPATH_MAGIC	"GEOM::MULTIPATH"
+
+#include <sys/endian.h>
+
+#ifdef	_KERNEL
+
+struct g_multipath_softc {
+	struct g_provider *	pp;
+	struct g_consumer *	cp_active;
+	char			sc_name[16];
+	char			sc_uuid[40];
+};
+#endif	/* _KERNEL */
+
+struct g_multipath_metadata {
+	char		md_magic[16];	/* Magic Value */
+	char 		md_uuid[40];	/* more magic */
+	char		md_name[16];	/* a friendly name */
+	uint32_t	md_version;	/* version */
+	uint32_t	md_sectorsize;	/* sectorsize of provider */
+	uint64_t	md_size;	/* absolute size of provider */
+};
+
+static __inline void
+multipath_metadata_encode(const struct g_multipath_metadata *, u_char *);
+
+static __inline void
+multipath_metadata_decode(u_char *, struct g_multipath_metadata *);
+
+static __inline void
+multipath_metadata_encode(const struct g_multipath_metadata *md, u_char *data)
+{
+	bcopy(md->md_magic, data, sizeof(md->md_magic));
+	data += sizeof(md->md_magic);
+	bcopy(md->md_uuid, data, sizeof(md->md_uuid));
+	data += sizeof(md->md_uuid);
+	bcopy(md->md_name, data, sizeof(md->md_name));
+	data += sizeof(md->md_name);
+	le32enc(data, md->md_version);
+	data += sizeof(md->md_version);
+	le32enc(data, md->md_sectorsize);
+	data += sizeof(md->md_sectorsize);
+	le64enc(data, md->md_size);
+}
+
+static __inline void
+multipath_metadata_decode(u_char *data, struct g_multipath_metadata *md)
+{
+	bcopy(data, md->md_magic, sizeof(md->md_magic));
+	data += sizeof(md->md_magic);
+	bcopy(data, md->md_uuid, sizeof(md->md_uuid));
+	data += sizeof(md->md_uuid);
+	bcopy(data, md->md_name, sizeof(md->md_name));
+	data += sizeof(md->md_name);
+	md->md_version = le32dec(data);
+	data += sizeof(md->md_version);
+	md->md_sectorsize = le32dec(data);
+	data += sizeof(md->md_sectorsize);
+	md->md_size = le64dec(data);
+}
+#endif	/* _G_MULTIPATH_H_ */