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freebsd/sys/geom/multipath/g_multipath.h
Matt Jacob e770bc6bf5 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
2007-02-27 04:01:58 +00:00

100 lines
3.4 KiB
C

/*-
* 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_ */