Re: refactoring basebackup.c

+ if (opt->compression == BACKUP_COMPRESSION_LZ4)

else if

+ /* First of all write the frame header to destination buffer. */
+ Assert(CHUNK_SIZE >= LZ4F_HEADER_SIZE_MAX);
+ headerSize = LZ4F_compressBegin(mysink->ctx,
+ mysink->base.bbs_next->bbs_buffer,
+ CHUNK_SIZE,
+ prefs);

I think this is wrong. I think you should be passing bbs_buffer_length
instead of CHUNK_SIZE, and I think you can just delete CHUNK_SIZE. If
you think otherwise, why?

+ * sink's bbs_buffer of length that can accomodate the compressed input

Spelling.

+ * Make it next multiple of BLCKSZ since the buffer length is expected so.

The buffer length is expected to be a multiple of BLCKSZ, so round up.

+ * If we are falling short of available bytes needed by
+ * LZ4F_compressUpdate() per the upper bound that is decided by
+ * LZ4F_compressBound(), send the archived contents to the next sink to
+ * process it further.

If the number of available bytes has fallen below the value computed
by LZ4F_compressBound(), ask the next sink to process the data so that
we can empty the buffer.