buffer: implement list::get_contiguous

Return a pointer to a contiguous range of the bufferlist, rebuilding
into a contiguous region as needed.  For now, if we need to rebuild,
we just do the whole thing.  We can obviously optimize this later to
rebuild on the necessary region, but this is good enough for the
(presumably) common case where the needed region is already in fact
contiguous.

Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #2849 from ceph/wip-buffer

RFC: buffer: implement list::get_contiguous

Reviewed-by: Haomai Wang <haomaiwang@gmail.com>
doc: Update for OpenStack Juno.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
Merge pull request #2854 from ceph/wip-doc-openstack-juno

doc: Update for OpenStack Juno.

New users working with Nova (Juno) noted that libvirt settings are now under a [libvirt] section, and truncate the leading libvirt_. Made subsections for Havana and Icehouse, added a new subsection for Juno.
doc: Added Key/Value store config reference to index.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Edited Key/Value store config reference.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
osd: cache pool: flush object ignoring cache min flush age when cache pool is full
Signed-off-by: Xinze Chi <xmdxcxz@gmail.com>
Merge pull request #2856 from XinzeChi/master

osd: cache pool: flush object ignoring cache min flush age when cache pool is full

Backport: giant, firefly
Reviewed-by: Sage Weil <sage@redhat.com>
buffer: Add _memcopy_count to track total count of memcopy by rebuild/rebuild_page_aligned/c_str.

Using thie filed, we know the payload of
rebuild/rebuild_page_aligned/c_str and tune performance accroding.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
Reviewed-by: Sage Weil <sage@redhat.com>
ObjectStore: Don't use largest_data_off to calc data_align.

If largest_data_off % CEPH_PAGE_SIZE != 0, the get_data_aligment return
a erro value. This make the FileJouranl::align_bl to memcopy much data.

Tested-by: Sage Weil <sage@redhat.com>
Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
ObjectStore: Fix a error comment.

Reviewed-by: Sage Weil <sage@redhat.com>
Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>