jbd2: add a helper to find out number of fast commit blocks

Add a helper to read number of fast commit blocks from jbd2 superblock
and also rename the JBD2_MIN_FC_BLKS to
JBD2_DEFAULT_FAST_COMMIT_BLOCKS since this constant is just the
default number of fast commit blocks to use in case number of fast
commit blocks isn't set in jbd2 superblock.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20201120202232.2240293-2-harshadshirwadkar@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
(cherry picked from commit 9bd23c31f392bda88618008f27fd52ee9e0fac38)
Change-Id: I9bee4efed33d1b8b5ee2f6f7ce0a84302ec719b5
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/10967
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Harshad Shirwadkar <harshads@google.com>
2 files changed