The function read_extent_from_disk() is only a wrapper to read tree
block.
And read_extent_data() is just a while loop to eliminate short read
caused by stripe boundary.
In fact, a lot of call sites of read_extent_data() are either reading
metadata (thus no possible short read) or doing extra loop by
themselves.
This patch will replace those two functions with read_data_from_disk(),
making it the only entrance for data/metadata read.
And update read_data_from_disk() to return the read bytes, so caller can
do a simple while loop.
For the few callers of read_extent_data(), open-code a small while loop
for them.
This will allow later RAID56 read repair using P/Q much easier.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
