[PATCH v8 28/35] dyndbg-doc: explain flags parse 1st

[Jim Cromie <jim.cromie@gmail.com>]

When writing queries to >control, flags are parsed 1st, since they are
the only required field.  So if the flags draw an error, then keyword
errors aren't reported.  This can be mildly confusing/annoying, so
explain it instead.

This note could be moved up to just after the grammar id's the flags,
and before the match-spec is detailed.  Opinions ?

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 Documentation/admin-guide/dynamic-debug-howto.rst | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 7b570f29ae98..ccf3704f2143 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -106,6 +106,16 @@ The match-spec's select *prdbgs* from the catalog, upon which to apply
 the flags-spec, all constraints are ANDed together.  An absent keyword
 is the same as keyword "*".
 
+Note: because the match-spec can be empty, the flags are checked 1st,
+then the pairs of keyword values.  Flag errs will hide keyword errs:
+
+  bash-5.2# ddcmd mod bar +foo
+  dyndbg: read 13 bytes from userspace
+  dyndbg: query 0: "mod bar +foo" mod:*
+  dyndbg: unknown flag 'o'
+  dyndbg: flags parse failed
+  dyndbg: processed 1 queries, with 0 matches, 1 errs
+
 A match specification is a keyword, which selects the attribute of
 the callsite to be compared, and a value to compare against.  Possible
 keywords are:::
-- 
2.44.0