[PATCH v5 3/5] alloc_tag: Add a flags field to allocinfo_filter

[Abhishek Bapat <abhishekbapat@google.com>]

struct allocinfo_filter uses a whole __u64 to hold the single boolean
used by the accuracy filter. Adding another boolean criterion the same
way would grow struct allocinfo_get_at, which changes the
ALLOCINFO_IOC_GET_AT ioctl number and breaks the UAPI.

Add a `flags` field that shares storage with `inaccurate` through an
anonymous union, and use bit 0, ALLOCINFO_FILTER_FLAG_INACCURATE, for
the accuracy criterion. New boolean criteria can take the remaining
bits without changing the struct layout.

Keeping `inaccurate` in the union means userspace built against the
older API still compiles, and the values 0 and 1 keep their meaning.
Previously any non-zero value selected inaccurate tags; now only bit 0
is checked, so a value such as 2 selects accurate tags instead.

Signed-off-by: Abhishek Bapat <abhishekbapat@google.com>
---
 include/uapi/linux/alloc_tag.h | 16 ++++++++++++++--
 mm/alloc_tag.c                 |  2 +-
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h
index dafcba2f7e2c..2fc843bb06bc 100644
--- a/include/uapi/linux/alloc_tag.h
+++ b/include/uapi/linux/alloc_tag.h
@@ -68,13 +68,25 @@ enum {
 #define ALLOCINFO_FILTER_MASKS \
 	((1 << (__ALLOCINFO_FILTER_LAST + 1)) - 1)
 
+#define ALLOCINFO_FILTER_FLAG_INACCURATE	(1ULL << 0)
+
 struct allocinfo_filter {
 	__u64 mask; /* bitmask of the filter fields used */
 	struct allocinfo_tag fields;
 	__u64 min_size;
 	__u64 max_size;
-	/* filter criteria only; see allocinfo_counter.accurate for actual accuracy */
-	__u64 inaccurate;
+	/*
+	 * Filter criteria only; see allocinfo_counter for the actual state.
+	 * Set ALLOCINFO_FILTER_FLAG_* bits in flags for the criteria selected
+	 * in mask. inaccurate is kept as an alias of flags so that userspace
+	 * built against the older API still compiles. Note that only
+	 * ALLOCINFO_FILTER_FLAG_INACCURATE is checked, so a non-zero value
+	 * with bit 0 clear no longer selects inaccurate tags.
+	 */
+	union {
+		__u64 inaccurate;
+		__u64 flags;
+	};
 };
 
 struct allocinfo_get_at {
diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index 9ff9dd04d692..504c1a85050d 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -306,7 +306,7 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,
 
 	if (filter->mask & ALLOCINFO_FILTER_MASK_INACCURATE) {
 		inaccurate = alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));
-		if (inaccurate != !!(filter->inaccurate))
+		if (inaccurate != !!(filter->flags & ALLOCINFO_FILTER_FLAG_INACCURATE))
 			return false;
 	}
 
-- 
2.56.0.506.g506a7eabc5-goog