[patch 0/2] [V4] block: Support online resize of disk partitions

[vgoyal@redhat.com]

Hi,

Few people have pinged me in rencent past about status of this patch, hence,
this is V4 of patch which adds support for online resizing of a partition.
This patch is based on previously posted patches by Phillip Susi. 

There are two patches. Out of which one is kernel patch and other one is
util-linux patch to add support of a user space utility "resizepart" to
allow resizing the partition.

This ioctl only resizes the partition size in kenrel and does not change
the size on disk. A user needs to make sure that corresponding changes
are made to disk data structures also using fdisk(or partx), if changes
are to be retained across reboot.

Changes since V3
----------------
- Do bdput() in error path as per the Maxim's review comments.

Changes since V2
----------------
- Do not ignore the "start" parameter in RESIZE ioctl.
- Change resizepart utility to parse sysfs to get to partition start.

Changes since V1
----------------
Following are changes since the version Phillip posted.
- RESIZE ioctl ignores the partition "start" and does not expect user to
  specify one. Caller needs to just specify "device", "partition number" and
  "size" of new partition.

- Got rid of part_nr_sects_write_begin/part_nr_sects_write_end functions
  and replaced these with single part_nr_sects_write().

- Some sequence counter related changes are simply lifted from i_size_write().

- Initialized part->nr_sects_seq using seqcount_init().

Phillip, do let me know if I should put your signed-off-by also in the
patch.

Any review feedback is welcome.

I did following test.

- Create a partition of 10MB on a disk using fdisk.
- Add this partition to a volume group
- Use fdisk to increase the partition size to 20MB. (First delete the
  partition and then create a new one of 20MB size).
- Use resizepart to extend partition size in kernel.
        resizepart /dev/sdc 1 40960
- Do pvresize on partition so that physical volume can be incrased in
  size online.
        pvresize /dev/sda1

pvresize does recognize the new size. Also lsblk and /proc/partitions
report the new size of partition.

Thanks
Vivek