libbe(3): rewrite init to support chroot usage

libbe(3) currently uses zfs_be_root and locates which of its children is
currently mounted at "/". This is reasonable, but not correct in the case of
a chroot, for two reasons:

- chroot root may be of a different zpool than zfs_be_root
- chroot root will not show up as mounted at "/"

Fix both of these by rewriting libbe_init to work from the rootfs down.
zfs_path_to_zhandle on / will resolve to the dataset mounted at the new
root, rather than the real root. From there, we can derive the BE root/pool
and grab the bootfs off of the new pool. This does no harm in the average
case, and opens up bectl to operating on different pools for scenarios where
one may be, for instance, updating a pool that generally gets re-rooted into
from a separate UFS root or zfs bootpool.

While here, I've also:
- Eliminated the check for /boot and / to be on the same partition. This
  leaves one open to a setup where /boot (and consequently, kernel/modules)
  are not included in the boot environment. This may very well be an
  intentional setup done by someone that knows what they're doing, we should
  not kill BE usage because of it.

- Eliminated the validation bits of BEs and snapshots that enforced
  'mountpoint' to be "/" -- this broke when trying to operate on an imported
  pool with an altroot, but we need not be this picky.

Reported by:	philip
Reviewed by:	philip, allanjude (previous version)
Tested by:	philip
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D18012

2 files changed, 19 insertions, 99 deletions

diff --git a/lib/libbe/be.c b/lib/libbe/be.c
index 540fe44ea1e9..46edcebc613a 100644
--- a/lib/libbe/be.c
+++ b/lib/libbe/be.c
@@ -29,11 +29,12 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <sys/param.h>
+#include <sys/mount.h>
 #include <sys/stat.h>
-#include <sys/types.h>
+#include <sys/ucred.h>
 
 #include <ctype.h>
-#include <kenv.h>
 #include <libgen.h>
 #include <libzfs_core.h>
 #include <stdio.h>
@@ -55,23 +56,16 @@ static int be_create_child_cloned(libbe_handle_t *lbh, const char *active);
  * zfs_be_root set by loader(8).  data is expected to be a libbe_handle_t *.
  */
 static int
-be_locate_rootfs(zfs_handle_t *chkds, void *data)
+be_locate_rootfs(libbe_handle_t *lbh)
 {
-	libbe_handle_t *lbh;
-	char *mntpoint;
-
-	lbh = (libbe_handle_t *)data;
-	if (lbh == NULL)
-		return (1);
+	zfs_handle_t *zfs;
 
-	mntpoint = NULL;
-	if (zfs_is_mounted(chkds, &mntpoint) && strcmp(mntpoint, "/") == 0) {
-		strlcpy(lbh->rootfs, zfs_get_name(chkds), sizeof(lbh->rootfs));
-		free(mntpoint);
+	zfs = zfs_path_to_zhandle(lbh->lzh, "/", ZFS_TYPE_FILESYSTEM);
+	if (zfs == NULL)
 		return (1);
-	} else if(mntpoint != NULL)
-		free(mntpoint);
 
+	strlcpy(lbh->rootfs, zfs_get_name(zfs), sizeof(lbh->rootfs));
+	zfs_close(zfs);
 	return (0);
 }
 
@@ -82,33 +76,12 @@ be_locate_rootfs(zfs_handle_t *chkds, void *data)
 libbe_handle_t *
 libbe_init(void)
 {
-	struct stat sb;
-	dev_t root_dev, boot_dev;
 	libbe_handle_t *lbh;
-	zfs_handle_t *rootds;
 	char *poolname, *pos;
 	int pnamelen;
 
 	lbh = NULL;
 	poolname = pos = NULL;
-	rootds = NULL;
-
-	/* Verify that /boot and / are mounted on the same filesystem */
-	/* TODO: use errno here?? */
-	if (stat("/", &sb) != 0)
-		goto err;
-
-	root_dev = sb.st_dev;
-
-	if (stat("/boot", &sb) != 0)
-		goto err;
-
-	boot_dev = sb.st_dev;
-
-	if (root_dev != boot_dev) {
-		fprintf(stderr, "/ and /boot not on same device, quitting\n");
-		goto err;
-	}
 
 	if ((lbh = calloc(1, sizeof(libbe_handle_t))) == NULL)
 		goto err;
@@ -116,15 +89,16 @@ libbe_init(void)
 	if ((lbh->lzh = libzfs_init()) == NULL)
 		goto err;
 
-	/* Obtain path to boot environment root */
-	if ((kenv(KENV_GET, "zfs_be_root", lbh->root,
-	    sizeof(lbh->root))) == -1)
+	/* Grab rootfs, we'll work backwards from there */
+	if (be_locate_rootfs(lbh) != 0)
 		goto err;
 
-	/* Remove leading 'zfs:' if present, otherwise use value as-is */
-	if (strcmp(lbh->root, "zfs:") == 0)
-		strlcpy(lbh->root, strchr(lbh->root, ':') + sizeof(char),
-		    sizeof(lbh->root));
+	/* Strip off the final slash from the rootfs to get the be root */
+	strlcpy(lbh->root, lbh->rootfs, sizeof(lbh->root));
+	pos = strrchr(lbh->root, '/');
+	if (pos == NULL)
+		goto err;
+	*pos = '\0';
 
 	if ((pos = strchr(lbh->root, '/')) == NULL)
 		goto err;
@@ -144,17 +118,6 @@ libbe_init(void)
 	    sizeof(lbh->bootfs), NULL, true) != 0)
 		goto err;
 
-	/* Obtain path to boot environment rootfs (currently booted) */
-	/* XXX Get dataset mounted at / by kenv/GUID from mountroot? */
-	if ((rootds = zfs_open(lbh->lzh, lbh->root, ZFS_TYPE_DATASET)) == NULL)
-		goto err;
-
-	zfs_iter_filesystems(rootds, be_locate_rootfs, lbh);
-	zfs_close(rootds);
-	rootds = NULL;
-	if (*lbh->rootfs == '\0')
-		goto err;
-
 	return (lbh);
 err:
 	if (lbh != NULL) {
@@ -503,10 +466,6 @@ be_create_from_existing(libbe_handle_t *lbh, const char *name, const char *old)
 int
 be_validate_snap(libbe_handle_t *lbh, const char *snap_name)
 {
-	zfs_handle_t *zfs_hdl;
-	char buf[BE_MAXPATHLEN];
-	char *delim_pos;
-	int err = BE_ERR_SUCCESS;
 
 	if (strlen(snap_name) >= BE_MAXPATHLEN)
 		return (BE_ERR_PATHLEN);
@@ -515,27 +474,7 @@ be_validate_snap(libbe_handle_t *lbh, const char *snap_name)
 	    ZFS_TYPE_SNAPSHOT))
 		return (BE_ERR_NOENT);
 
-	strlcpy(buf, snap_name, sizeof(buf));
-
-	/* Find the base filesystem of the snapshot */
-	if ((delim_pos = strchr(buf, '@')) == NULL)
-		return (BE_ERR_INVALIDNAME);
-	*delim_pos = '\0';
-
-	if ((zfs_hdl =
-	    zfs_open(lbh->lzh, buf, ZFS_TYPE_DATASET)) == NULL)
-		return (BE_ERR_NOORIGIN);
-
-	if ((err = zfs_prop_get(zfs_hdl, ZFS_PROP_MOUNTPOINT, buf,
-	    sizeof(buf), NULL, NULL, 0, 1)) != 0)
-		err = BE_ERR_BADMOUNT;
-
-	if ((err != 0) && (strncmp(buf, "/", sizeof(buf)) != 0))
-		err = BE_ERR_BADMOUNT;
-
-	zfs_close(zfs_hdl);
-
-	return (err);
+	return (BE_ERR_SUCCESS);
 }
 
 
diff --git a/lib/libbe/be_info.c b/lib/libbe/be_info.c
index dba718cbac8f..8a6038009b82 100644
--- a/lib/libbe/be_info.c
+++ b/lib/libbe/be_info.c
@@ -289,30 +289,11 @@ int
 be_exists(libbe_handle_t *lbh, char *be)
 {
 	char buf[BE_MAXPATHLEN];
-	nvlist_t *dsprops;
-	char *mntpoint;
-	bool valid;
 
 	be_root_concat(lbh, be, buf);
 
 	if (!zfs_dataset_exists(lbh->lzh, buf, ZFS_TYPE_DATASET))
 		return (BE_ERR_NOENT);
 
-	/* Also check if it's mounted at / */
-	if (be_prop_list_alloc(&dsprops) != 0)
-		return (BE_ERR_UNKNOWN);
-
-	if (be_get_dataset_props(lbh, buf, dsprops) != 0) {
-		nvlist_free(dsprops);
-		return (BE_ERR_UNKNOWN);
-	}
-
-	if (nvlist_lookup_string(dsprops, "mountpoint", &mntpoint) == 0) {
-		valid = (strcmp(mntpoint, "/") == 0);
-		nvlist_free(dsprops);
-		return (valid ? BE_ERR_SUCCESS : BE_ERR_BADMOUNT);
-	}
-
-	nvlist_free(dsprops);
-	return (BE_ERR_BADMOUNT);
+	return (BE_ERR_SUCCESS);
 }