Ensure that zfs diff prints unicode safely.

In the stream_bytes() library function used by `zfs diff`, explicitly
cast each byte in the input string to an unsigned character so that the
Linux fprintf() correctly escapes to octal and does not mangle the output.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1172
Fix quoting error in unmount command

A misplaced single quote caused the umount command to fail with a
syntax error when unmounting snapshots under the .zfs/snapshot
control directory.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1210
Fix false ENOENT on snapshot control dentries

Lookups in the snapshot control directory for an existing snapshot
fail with ENOENT if an earlier lookup failed before the snapshot was
created.  This is because the earlier lookup causes a negative dentry
to be cached which is never invalidated.

The bug can be reproduced as follows (the second ls should succeed):

 $ ls /tank/.zfs/snapshot/s
 ls: cannot access /tank/.zfs/snapshot/s: No such file or directory
 $ zfs snap tank@s
 $ ls /tank/.zfs/snapshot/s
 ls: cannot access /tank/.zfs/snapshot/s: No such file or directory

To remedy this, always invalidate cached dentries in the snapshot
control directory.  Since these entries never exist on disk there is
no significant performance penalty for the extra lookups.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1192
Fix 'zfs rollback' on mounted file systems

Rolling back a mounted filesystem with open file handles and
cached dentries+inodes never worked properly in ZoL.  The
major issue was that Linux provides no easy mechanism for
modules to invalidate the inode cache for a file system.

Because of this it was possible that an inode from the previous
filesystem would not get properly dropped from the cache during
rolling back.  Then a new inode with the same inode number would
be create and collide with the existing cached inode.  Ideally
this would trigger an VERIFY() but in practice the error wasn't
handled and it would just NULL reference.

Luckily, this issue can be resolved by sprucing up the existing
Solaris zfs_rezget() functionality for the Linux VFS.

The way it works now is that when a file system is rolled back
all the cached inodes will be traversed and refetched from disk.
If a version of the cached inode exists on disk the in-core
copy will be updated accordingly.  If there is no match for that
object on disk it will be unhashed from the inode cache and
marked as stale.

This will effectively make the inode unfindable for lookups
allowing the inode number to be immediately recycled.  The inode
will then only be accessible from the cached dentries.  Subsequent
dentry lookups which reference a stale inode will result in the
dentry being invalidated.  Once invalidated the dentry will drop
its reference on the inode allowing it to be safely pruned from
the cache.

Special care is taken for negative dentries since they do not
reference any inode.  These dentires will be invalidate based
on when they were added to the dentry cache.  Entries added
before the last rollback will be invalidate to prevent them
from masking real files in the dataset.

Two nice side effects of this fix are:

* Removes the dependency on spl_invalidate_inodes(), it can now
  be safely removed from the SPL when we choose to do so.

* zfs_znode_alloc() no longer requires a dentry to be passed.
  This effectively reverts this portition of the code to its
  upstream counterpart.  The dentry is not instantiated more
  correctly in the Linux ZPL layer.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Closes #795
Revert "Revert "Fix unlink/xattr deadlock""

This reverts commit 53c7411919a64d6f0889aa0d6974610f6cd35744
effectively reinstating the asynchronous xattr cleanup code.

These Linux changes were reverted because after testing
and careful contemplation I was convinced that due to the
89260a1c8851ce05ea04b23606ba438b271d890 commit they were no
longer required.

Unfortunately, the deadlock described in #1176  was a case
which wasn't considered.  At mount zfs_unlinked_drain() can
occur which will unlink a list of znodes in effectively a
random order which isn't safe.  The only reason it was safe
to originally revert this change was the we could guarantee
that the VFS would always prune the xattr leaves before the
parents.

Therefore, until we can cleanly resolve this deadlock for
all cases we need to keep this change in spite of the xattr
unlink performance penalty associated with it.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1176
Issue #457
Fix zpool on zvol deadlock

Commit 65d56083b4617a4cade0cff68cbbaf68114169d6 fixes the lock
inversion between spa_namespace_lock and bdev->bd_mutex but only
for the first user of spa_namespace_lock: dmu_objset_own().
Later spa_namespace_lock gets acquired by dsl_prop_get_integer()
though dsl_prop_get()->dsl_dataset_hold()->dsl_dir_open_spa()->
spa_open()->spa_open_common() without this "protection".  By
moving the mutex release after this second use, even this
acquisition of the lock is "protected" by the ERESTARTSYS trick.

Signed-off-by: Massimo Maggi <me@massimo-maggi.eu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1220
Use sb->s_d_op default dentry operations

As of Linux 2.6.37 the right way to register custom dentry
operations is to use the super block's ->s_d_op field.
For older kernels they should be registered as part of the
lookup operation.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1223