Illumos #2882, #2883, #2900

2882 implement libzfs_core
2883 changing "canmount" property to "on" should not always remount dataset
2900 "zfs snapshot" should be able to create multiple, arbitrary snapshots at once

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Chris Siden <christopher.siden@delphix.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Reviewed by: Bill Pijewski <wdp@joyent.com>
Reviewed by: Dan Kruchinin <dan.kruchinin@gmail.com>
Approved by: Eric Schrock <Eric.Schrock@delphix.com>

References:
  https://www.illumos.org/issues/2882
  https://www.illumos.org/issues/2883
  https://www.illumos.org/issues/2900
  illumos/illumos-gate@4445fffbbb

Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1293

Porting notes:

WARNING: This patch changes the user/kernel ABI.  That means that
the zfs/zpool utilities built from master are NOT compatible with
the 0.6.2 kernel modules.  Ensure you load the matching kernel
modules from master after updating the utilities.  Otherwise the
zfs/zpool commands will be unable to interact with your pool and
you will see errors similar to the following:

  $ zpool list
  failed to read pool configuration: bad address
  no pools available

  $ zfs list
  no datasets available

Add zvol minor device creation to the new zfs_snapshot_nvl function.

Remove the logging of the "release" operation in
dsl_dataset_user_release_sync().  The logging caused a null dereference
because ds->ds_dir is zeroed in dsl_dataset_destroy_sync() and the
logging functions try to get the ds name via the dsl_dataset_name()
function. I've got no idea why this particular code would have worked
in Illumos.  This code has subsequently been completely reworked in
Illumos commit 3b2aab1 (3464 zfs synctask code needs restructuring).

Squash some "may be used uninitialized" warning/erorrs.

Fix some printf format warnings for %lld and %llu.

Apply a few spa_writeable() changes that were made to Illumos in
illumos/illumos-gate.git@cd1c8b8 as part of the 3112, 3113, 3114 and
3115 fixes.

Add a missing call to fnvlist_free(nvl) in log_internal() that was added
in Illumos to fix issue 3085 but couldn't be ported to ZoL at the time
(zfsonlinux/zfs@9e11c73) because it depended on future work.

include/sys/dmu.h

@@ -42,6 +42,7 @@
 #include <sys/param.h>
 #include <sys/cred.h>
 #include <sys/time.h>
+#include <sys/fs/zfs.h>
 #include <sys/uio.h>
 
 #ifdef	__cplusplus
@@ -213,16 +214,6 @@ typedef enum dmu_object_type {
 	DMU_OTN_ZAP_METADATA = DMU_OT(DMU_BSWAP_ZAP, B_TRUE),
 } dmu_object_type_t;
 
-typedef enum dmu_objset_type {
-	DMU_OST_NONE,
-	DMU_OST_META,
-	DMU_OST_ZFS,
-	DMU_OST_ZVOL,
-	DMU_OST_OTHER,			/* For testing only! */
-	DMU_OST_ANY,			/* Be careful! */
-	DMU_OST_NUMTYPES
-} dmu_objset_type_t;
-
 void byteswap_uint64_array(void *buf, size_t size);
 void byteswap_uint32_array(void *buf, size_t size);
 void byteswap_uint16_array(void *buf, size_t size);
@@ -267,9 +258,11 @@ int dmu_objset_create(const char *name, dmu_objset_type_t type, uint64_t flags,
 int dmu_objset_clone(const char *name, struct dsl_dataset *clone_origin,
     uint64_t flags);
 int dmu_objset_destroy(const char *name, boolean_t defer);
-int dmu_snapshots_destroy_nvl(struct nvlist *snaps, boolean_t defer, char *);
-int dmu_objset_snapshot(char *fsname, char *snapname, char *tag,
-    struct nvlist *props, boolean_t recursive, boolean_t temporary, int fd);
+int dmu_snapshots_destroy_nvl(struct nvlist *snaps, boolean_t defer,
+    struct nvlist *errlist);
+int dmu_objset_snapshot(struct nvlist *snaps, struct nvlist *, struct nvlist *);
+int dmu_objset_snapshot_one(const char *fsname, const char *snapname);
+int dmu_objset_snapshot_tmp(const char *, const char *, int);
 int dmu_objset_rename(const char *name, const char *newname,
     boolean_t recursive);
 int dmu_objset_find(char *name, int func(const char *, void *), void *arg,
@@ -792,10 +785,9 @@ typedef void (*dmu_traverse_cb_t)(objset_t *os, void *arg, struct blkptr *bp,
 void dmu_traverse_objset(objset_t *os, uint64_t txg_start,
     dmu_traverse_cb_t cb, void *arg);
 
-int dmu_send(objset_t *tosnap, objset_t *fromsnap, boolean_t fromorigin,
+int dmu_send(objset_t *tosnap, objset_t *fromsnap,
     int outfd, struct vnode *vp, offset_t *off);
-int dmu_send_estimate(objset_t *tosnap, objset_t *fromsnap, boolean_t fromorign,
-    uint64_t *sizep);
+int dmu_send_estimate(objset_t *tosnap, objset_t *fromsnap, uint64_t *sizep);
 
 typedef struct dmu_recv_cookie {
 	/*