[PATCH 07/18] log: Add filter flag to deny on match

[Sean Anderson <seanga2@gmail.com>]

Without this flag, log filters can only explicitly accept messages.
Allowing denial makes it easier to filter certain subsystems. Unlike
allow-ing filters, deny-ing filters are added to the beginning of the
filter list. This should do the Right Thing most of the time, but it's
less-universal than allowing filters to be inserted anywhere. If this
becomes a problem, then perhaps log_filter_add* should take a filter number
to insert before/after.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
---

 common/log.c  | 12 ++++++++++--
 include/log.h | 11 ++++++++++-
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/common/log.c b/common/log.c
index b42c4fad60..0b9071ba1c 100644
--- a/common/log.c
+++ b/common/log.c
@@ -178,7 +178,11 @@ static bool log_passes_filters(struct log_device *ldev, struct log_rec *rec)
 		if (filt->file_list &&
 		    !log_has_file(filt->file_list, rec->file))
 			continue;
-		return true;
+
+		if (filt->flags & LOGFF_DENY)
+			return false;
+		else
+			return true;
 	}
 
 	return false;
@@ -280,7 +284,11 @@ int log_add_filter_flags(const char *drv_name, enum log_category_t cat_list[],
 		}
 	}
 	filt->filter_num = ldev->next_filter_num++;
-	list_add_tail(&filt->sibling_node, &ldev->filter_head);
+	/* Add deny filters to the beginning of the list */
+	if (flags & LOGFF_DENY)
+		list_add(&filt->sibling_node, &ldev->filter_head);
+	else
+		list_add_tail(&filt->sibling_node, &ldev->filter_head);
 
 	return filt->filter_num;
 
diff --git a/include/log.h b/include/log.h
index 9116466fcf..00647cafbd 100644
--- a/include/log.h
+++ b/include/log.h
@@ -338,13 +338,22 @@ enum {
 	LOGF_MAX_CATEGORIES = 5,	/* maximum categories per filter */
 };
 
+/**
+ * enum log_filter_flags - Flags which modify a filter
+ */
 enum log_filter_flags {
-	LOGFF_HAS_CAT		= 1 << 0,	/* Filter has a category list */
+	/** @LOGFF_HAS_CAT: Filter has a category list */
+	LOGFF_HAS_CAT	= 1 << 0,
+	/** @LOGFF_DENY: Filter denies matching messages */
+	LOGFF_DENY	= 1 << 1,
 };
 
 /**
  * struct log_filter - criterial to filter out log messages
  *
+ * If a message matches all criteria, then it is allowed. If LOGFF_DENY is set,
+ * then it is denied instead.
+ *
  * @filter_num: Sequence number of this filter.  This is returned when adding a
  *	new filter, and must be provided when removing a previously added
  *	filter.
-- 
2.28.0