Btrfs: Add device replace code

This patch series adds support for replacing disks at runtime.

It replaces the following steps in case a disk was lost:
mount ... -o degraded
btrfs device add new_disk
btrfs device delete missing

Or in case a disk just needs to be replaced because the error rate is increasing:
btrfs device add new_disk
btrfs device delete old_disk

Instead just run:
btrfs replace mountpoint old_disk new_disk

The device replace operation takes place at runtime on a live filesystem, you don't need to unmount it or stop active tasks. It is safe to crash or lose power during the operation, the process resumes with the next mount.

The copy usually takes place at 90% of the available platter speed if no additional disk I/O is ongoing during the copy operation, thus the degraded state without redundancy can be left quickly.

The copy process is started manually. It is a different project to react on an increased device I/O error rate with an automatic start of this procedure.

The patch series is based on btrfs-next and also available here:
git://btrfs.giantdisaster.de/git/btrfs device-replace

The user mode part is the top commit of
git://btrfs.giantdisaster.de/git/btrfs-progs master

replace start [-Bfr] <path> <srcdev>|<devid> <targetdev>
Replace device of a btrfs filesystem. On a live filesystem,
duplicate the data to the target device which is currently stored on the source device. If the source device is not avail- able anymore, or if the -r option is set, the data is built only using the RAID redundancy mechanisms. After completion of the operation, the source device is removed from the filesystem. If the srcdev is a numerical value, it is assumed to be the device id of the filesystem which is mounted at mount_point, otherwise is is the path to the source device. If the source device is disconnected, from the system, you have to use the devid parame- ter format. The targetdev needs to be same size or larger than the srcdev.

Options

-r only read from srcdev if no other zero-defect mirror
exists (enable this if your drive has lots of read errors, the access would be very slow)

-f force using and overwriting targetdev even if it looks
like containing a valid btrfs filesystem. A valid
filesystem is assumed if a btrfs superblock is found which contains a correct checksum. Devices which are cur- rently mounted are never allowed to be used as the tar- getdev

-B do not background

replace status [-1] <path>
Print status and progress information of a running device replace operation.

Options

-1 print once instead of print continously until the replace
operation finishes (or is canceled)

replace cancel <path>
Cancel a running device replace operation.

Stefan Behrens (26):
Btrfs: rename the scrub context structure
Btrfs: remove the block device pointer from the scrub context struct
Btrfs: make the scrub page array dynamically allocated
Btrfs: in scrub repair code, optimize the reading of mirrors
Btrfs: in scrub repair code, simplify alloc error handling
Btrfs: cleanup scrub bio and worker wait code
Btrfs: add two more find_device() methods
Btrfs: Pass fs_info to btrfs_num_copies() instead of mapping_tree
Btrfs: pass fs_info to btrfs_map_block() instead of mapping_tree
Btrfs: add btrfs_scratch_superblock() function
Btrfs: pass fs_info instead of root
Btrfs: avoid risk of a deadlock in btrfs_handle_error
Btrfs: enhance btrfs structures for device replace support
Btrfs: introduce a btrfs_dev_replace_item type
Btrfs: add a new source file with device replace code
Btrfs: disallow mutually exclusiv admin operations from user mode
Btrfs: disallow some operations on the device replace target device
Btrfs: handle errors from btrfs_map_bio() everywhere
Btrfs: add code to scrub to copy read data to another disk
Btrfs: change core code of btrfs to support the device replace
operations
Btrfs: introduce GET_READ_MIRRORS functionality for btrfs_map_block()
Btrfs: changes to live filesystem are also written to replacement
disk
Btrfs: optionally avoid reads from device replace source drive
Btrfs: increase BTRFS_MAX_MIRRORS by one for dev replace
Btrfs: allow repair code to include target disk when searching
mirrors
Btrfs: add support for device replace ioctls

 fs/btrfs/Makefile          |    2 +-
 fs/btrfs/check-integrity.c |   29 +-
 fs/btrfs/compression.c     |    6 +-
 fs/btrfs/ctree.h           |  127 ++-
 fs/btrfs/dev-replace.c     |  843 ++++++++++++++++++++
 fs/btrfs/dev-replace.h     |   44 ++
 fs/btrfs/disk-io.c         |   79 +-
 fs/btrfs/extent-tree.c     |    5 +-
 fs/btrfs/extent_io.c       |   28 +-
 fs/btrfs/extent_io.h       |    4 +-
 fs/btrfs/inode.c           |   39 +-
 fs/btrfs/ioctl.c           |  117 ++-
 fs/btrfs/ioctl.h           |   45 ++
 fs/btrfs/print-tree.c      |    3 +
 fs/btrfs/reada.c           |   31 +-
 fs/btrfs/scrub.c           | 1822 ++++++++++++++++++++++++++++++++------------
 fs/btrfs/super.c           |   30 +-
 fs/btrfs/transaction.c     |    7 +-
 fs/btrfs/volumes.c         |  624 +++++++++++++--
 fs/btrfs/volumes.h         |   26 +-
 20 files changed, 3244 insertions(+), 667 deletions(-)
 create mode 100644 fs/btrfs/dev-replace.c
 create mode 100644 fs/btrfs/dev-replace.h

1.8.0