Support triggering compaction of all files under a given directory

[SandyXSD]

What would you like to be added:
Support triggering compaction of all files under a given directory

Why is this needed:
An alternative light way of gc --compact for large clusters.

[jiefenghuang]

requirements

• A new user compact command
• Support triggering compaction of all files under a given directory

design

• what we have

  • meta.engine.compact(inode Ino, index uint32, force bool)

• what we should do

  • Iterate entries under specific path, get all set (inode, type, length)
  • For a file, calculate the chunk count based on its length. The chunk index ranges from 0 to (chunk count-1). Perform 'compact' operation on all chunks(maybe not exists).
    • chunkCount = (fileLength + chunkSize - 1) / chunkSize
    • Ensure that the 'compact' function behaves correctly for non-existent chunks.
    • For files with many chunk holes, performance is poor, but this scenario is infrequent. Currently, it is not being considered.

• alternative

  • get all inodes under specific path
  • use meta.scan to get all chunks