illumos gate

As reported on the zfs@illumos mailing list:

The send completes (if piped to receive, the receive finishes OK), but the sending process hangs. It should be easy to reproduce:

1. zfs create zones/one
2. zfs snapshot zones/one@test
3. zfs send zones/one@test | zfs receive -v zones/two
   receiving full stream of zones/one@test into zones/two@test
   received 46.3KB stream in 1 seconds (46.3KB/sec)
4. zfs destroy -r zones/two
5. zfs send -D zones/one@test | zfs receive -v zones/two
   receiving full stream of zones/one@test into zones/two@test
   received 46.3KB stream in 1 seconds (46.3KB/sec)
   ^C
   Hung!

The problem is that zfs_send() is calling pthread_join() before closing the pipe. The workaround of hitting ^C when it's done should work (at least in this simple case). This bug was introduced by the following commit:

Branch: refs/heads/master
Home: https://github.com/illumos/illumos-gate
Commit: a7a845e4bf22fd1b2a284729ccd95c7370a0438c
https://github.com/illumos/illumos-gate/commit/a7a845e4bf22fd1b2a284729ccd95c7370a0438c
Author: Steven Hartland <smh@freebsd.org>
Date: 2013-06-11 (Tue, 11 Jun 2013)

Changed paths:
    M usr/src/cmd/ndmpd/ndmp/ndmpd_chkpnt.c
    M usr/src/cmd/zfs/zfs_main.c
    M usr/src/cmd/zhack/zhack.c
    M usr/src/cmd/ztest/ztest.c
    M usr/src/lib/libzfs/common/libzfs.h
    M usr/src/lib/libzfs/common/libzfs_dataset.c
    M usr/src/lib/libzfs/common/libzfs_sendrecv.c
    M usr/src/lib/libzfs_core/common/libzfs_core.c
    M usr/src/uts/common/fs/zfs/dsl_destroy.c
    M usr/src/uts/common/fs/zfs/dsl_pool.c
    M usr/src/uts/common/fs/zfs/dsl_userhold.c
    M usr/src/uts/common/fs/zfs/sys/dsl_dataset.h
    M usr/src/uts/common/fs/zfs/sys/dsl_userhold.h
    M usr/src/uts/common/fs/zfs/zfs_ioctl.c

Log Message:
  -----------
  3740 Poor ZFS send / receive performance due to snapshot hold / release processing
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Christopher Siden <christopher.siden@delphix.com>