So with Xen one can export a "disk" (disk, file, LVM partiion, etc.)
with "access=ro", and that is enforced.
However if one tries to mount such a disk in a domU as root, it fails.
When one first looks at the code which does the initial vfs_mountroot it
would appear to be correct -- i.e. it is trying to open the root
filesystem device for reading it uses VOP_OPEN() to open the root
device with FREAD (which I think means "only for reading"):
error = VOP_OPEN(rootvp, FREAD, FSCRED);
if (error) {
printf("vfs_mountroot: can't open root device, error = %d\n", error);
return (error);
}
However something assumes that if it is like a disk (i.e. but not a
CD-ROM/DVD) then it tries to open for write too as we get:
root on dk1
vfs_mountroot: can't open root device, error = 30
cannot mount root, error = 30
(errno #30 is of course EROFS)
I'm not even sure where this is happening.
vfs_rootmountalloc() does indeed set MNT_RDONLY, but this error is
happening before vfs_mountroot() calls ffs_mountroot (through the
vfs_mountroot pointer).
So I'm lost -- any hints? Is it from bounds_check_with_label()? How?
--
Greg A. Woods <gwoods%acm.org@localhost>
Kelowna, BC +1 250 762-7675 RoboHack <woods%robohack.ca@localhost>
Planix, Inc. <woods%planix.com@localhost> Avoncote Farms <woods%avoncote.ca@localhost>
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