This patch will bring this interface up to our 3rd gen
standards. The following summarizes the major changes.
* New delta provisions have been added to most fields.
There are, of course, some fields for which a delta is
inappropriate. They include the identifying items such
as name, type, major and minor. Plus the io_inprogress
field which already acts, in effect, as a delta value.
* To provide delta support, dev_node historical values
have become persistent. By the same token, the library
must provide for future removal of disks/partitions. A
timestamp is used to detect 'stale' data which will be
deleted so as not to satisfy some get, select or reap.
* Such persistent support is provided by a linked list
which, by default, grows from the bottom down so as to
maintain compatibility with the /proc/diskstats order.
Initially, I was tempted to use the GNU tsearch (tree)
provisions until I discovered the overhead of building
that tree plus costs of a subsequent 'twalk'. Besides,
walking such a tree means retrieval order would differ
from an order required/expected by the vmstat program.
* The '/sys/block' directory is no longer scanned with
every refresh cycle. Rather, it's only accessed when a
node is first encountered. Then, that node's 'type' is
persistent for its lifetime like several other fields.
* A sort provision was included, at virtually no cost,
even though such a provision was not currently needed.
Signed-off-by: Jim Warner <james.warner@comcast.net>
ecd64f4445