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Checking if the underlying file system supports VOP_BMAP and VOP_STRATEGY does not imply that works.

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Test if VOP_BMAP actually works before using bmap/strategy.

When you create an image with

dd if=/dev/zero of=./netbsd.img bs=1m count=1 seek=1000

then the current check actually determines the "file system"
in the image supports VOP_BMAP and VOP_STRATEGY, but VOP_BMAP can't
translate any logical block numbers which results in EIO failures.

When you try to access the image in a Xen DomU you see all disk operations
failing. Therefore test if VOP_BMAP actually works and fall back to
VOP_READ/VOP_WRITE if it doesn't.

This makes a Xen DomU installation working. When you boot your fresh
installed Xen DomU with a valid disklabel and file system in the image,
VOP_BMAP actually works and is used.

This allows you to create an image with dd as above on the Dom0 and
run a DomU installation or to quickly create another virtual disk for
an existing DomU without having to create a disklabel and file system
by hand.
This commit is contained in:
cegger 2008-06-14 11:44:57 +00:00
parent 826cd7b39b
commit 75946855ff
1 changed files with 35 additions and 5 deletions
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40
sys/dev/vnd.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: vnd.c,v 1.183 2008/06/14 07:52:36 cegger Exp $ */
/* $NetBSD: vnd.c,v 1.184 2008/06/14 11:44:57 cegger Exp $ */
/*-
* Copyright (c) 1996, 1997, 1998, 2008 The NetBSD Foundation, Inc.
@ -130,7 +130,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vnd.c,v 1.183 2008/06/14 07:52:36 cegger Exp $");
__KERNEL_RCSID(0, "$NetBSD: vnd.c,v 1.184 2008/06/14 11:44:57 cegger Exp $");
#if defined(_KERNEL_OPT)
#include "fs_nfs.h"
@ -526,6 +526,37 @@ done:
splx(s);
}
static bool
vnode_has_strategy(struct vnd_softc *vnd)
{
return vnode_has_op(vnd->sc_vp, VOFFSET(vop_bmap)) &&
vnode_has_op(vnd->sc_vp, VOFFSET(vop_strategy));
}
static bool
vnode_strategy_probe(struct vnd_softc *vnd)
{
int error;
daddr_t nbn;
if (!vnode_has_strategy(vnd))
return false;
/* Convert the first logical block number to its
* physical block number.
*/
error = 0;
vn_lock(vnd->sc_vp, LK_EXCLUSIVE | LK_RETRY | LK_CANRECURSE);
error = VOP_BMAP(vnd->sc_vp, 0, NULL, &nbn, NULL);
VOP_UNLOCK(vnd->sc_vp, 0);
/* Test if that worked. */
if (error == 0 && (long)nbn == -1)
return false;
return true;
}
static void
vndthread(void *arg)
{
@ -533,13 +564,12 @@ vndthread(void *arg)
bool usestrategy;
int s;
/* Determine whether we can use VOP_BMAP and VOP_STRATEGY to
/* Determine whether we can *use* VOP_BMAP and VOP_STRATEGY to
* directly access the backing vnode. If we can, use these two
* operations to avoid messing with the local buffer cache.
* Otherwise fall back to regular VOP_READ/VOP_WRITE operations
* which are guaranteed to work with any file system. */
usestrategy = vnode_has_op(vnd->sc_vp, VOFFSET(vop_bmap)) &&
vnode_has_op(vnd->sc_vp, VOFFSET(vop_strategy));
usestrategy = vnode_strategy_probe(vnd);
#ifdef DEBUG
if (vnddebug & VDB_INIT)