While debugging a ENOSPC related performance problem I needed to see the
time difference between start and end of a reserve ticket, so add a
trace point to report when we handle a reserve ticket.

I opted to spit out start_ns itself without calculating the difference
because there could be a gap between enabling the tracpoint and setting
start_ns.  Doing it this way allows us to filter on 0 start_ns so we
don't get bogus entries, and we can easily calculate the time difference
with bpftrace or something else.

Reviewed-by: Nikolay Borisov <redacted>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/space-info.c        | 10 +++++++++-
 include/trace/events/btrfs.h | 29 +++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index ba2b72409d46..ac7269cf1904 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c

@@ -1224,6 +1224,7 @@ static void wait_reserve_ticket(struct btrfs_fs_info *fs_info,
 static int handle_reserve_ticket(struct btrfs_fs_info *fs_info,
 				 struct btrfs_space_info *space_info,
 				 struct reserve_ticket *ticket,
+				 u64 start_ns, u64 orig_bytes,