printk: ringbuffer: change representation of states

Rather than deriving the state by evaluating bits within the flags
area of the state variable, assign the states explicit values and
set those values in the flags area. Introduce macros to make it
simple to read and write state values for the state variable.

Although the functionality is preserved, the binary representation
for the states is changed.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200914123354.832-5-john.ogness@linutronix.de

scripts/gdb/linux/dmesg.py

@@ -78,10 +78,10 @@ class LxDmesg(gdb.Command):
         len_off = off + printk_info_type.get_type()['text_len'].bitpos // 8
 
         # definitions from kernel/printk/printk_ringbuffer.h
+        desc_committed = 1
         desc_sv_bits = utils.get_long_type().sizeof * 8
-        desc_committed_mask = 1 << (desc_sv_bits - 1)
-        desc_reuse_mask = 1 << (desc_sv_bits - 2)
-        desc_flags_mask = desc_committed_mask | desc_reuse_mask
+        desc_flags_shift = desc_sv_bits - 2
+        desc_flags_mask = 3 << desc_flags_shift
         desc_id_mask = ~desc_flags_mask
 
         # read in tail and head descriptor ids
@@ -96,8 +96,9 @@ class LxDmesg(gdb.Command):
             desc_off = desc_sz * ind
 
             # skip non-committed record
-            state = utils.read_u64(descs, desc_off + sv_off + counter_off) & desc_flags_mask
-            if state != desc_committed_mask:
+            state = 3 & (utils.read_u64(descs, desc_off + sv_off +
+                                        counter_off) >> desc_flags_shift)
+            if state != desc_committed:
                 if did == head_id:
                     break
                 did = (did + 1) & desc_id_mask