[PATCH 0/2] f2fs: multi-device expandable storage support

[李珂11 <ke.li11@transsion.com>]

From: "ke.li11" <ke.li11@transsion.com>

This series improves multi-device F2FS for expandable storage setups
where a secondary block device holds warm/cold data and may be removed
after userspace performs a final shrink.

Patch 1 adds an alloc_primary mount option.  By default F2FS steers
warm/cold allocations to the secondary device via ALLOC_NEXT; this
option keeps them on the primary device when required by userspace
volume management.

Patch 2 extends f2fs_resize_fs() to allow a section-aligned shrink
that fully removes the last secondary device.  The on-disk superblock
path for that device is cleared before commit so the next mount does
not try to open a block device that userspace is deleting.  The
in-memory device is detached only after both the superblock update and
checkpoint succeed; the path is restored if either step fails.

Testing:
- Mounted /data as a multi-device F2FS filesystem with a secondary expand
  device (device=exp_user_device)
- Exercised dynamic resize while the expand volume is attached
- Shrunk the filesystem until the entire exp_user_device is removed;
  this triggers the drop_last_dev path in f2fs_resize_fs()
- Verified remount succeeds after userspace tears down the expand
  block device
- Mounted with and without alloc_primary and verified allocation behavior

Signed-off-by: ke.li11 <ke.li11@transsion.com>

ke.li11 (2):
  f2fs: add alloc_primary mount option
  f2fs: allow f2fs_resize_fs to drop the last secondary device

 Documentation/filesystems/f2fs.rst |   3 +
 fs/f2fs/f2fs.h                     |   6 ++
 fs/f2fs/gc.c                       | 127 +++++++++++++++++++++++++++--
 fs/f2fs/super.c                    |  12 +++
 4 files changed, 143 insertions(+), 5 deletions(-)

-- 
2.34.1