[PATCH bpf-next v4 1/2] selftests/bpf: Move alloc_pagecache() to cgroup_helpers

[listout]

From: Brahmajit Das <bdas@xxxxxxx>

arena_memcg has a static alloc_pagecache() that fills the page cache
with clean, reclaimable pages by reading a sparse O_TMPFILE. The next
patch needs the same helper for the memcg kfunc tests.

Move it to cgroup_helpers.c, which test_progs already links, so both
tests share one copy and fixes to the reclaimability detection only
have to be made once.

No functional change.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Brahmajit Das <bdas@xxxxxxx>
---
 tools/testing/selftests/bpf/cgroup_helpers.c  | 34 +++++++++++++++++++
 tools/testing/selftests/bpf/cgroup_helpers.h  |  1 +
 .../selftests/bpf/prog_tests/arena_memcg.c    | 34 -------------------
 3 files changed, 35 insertions(+), 34 deletions(-)

diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c
index 4183ff6150c2..ace15b9cd2e4 100644
--- a/tools/testing/selftests/bpf/cgroup_helpers.c
+++ b/tools/testing/selftests/bpf/cgroup_helpers.c
@@ -5,6 +5,8 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/xattr.h>
+#include <sys/vfs.h>
+#include <linux/magic.h>
 #include <linux/limits.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -613,6 +615,38 @@ int cgroup_setup_and_join(const char *path) {
 	return cg_fd;
 }
 
+/*
+ * Fill the page cache with @size bytes of clean, reclaimable pages by
+ * reading a sparse temp file, the way the cgroup selftests do. Returns the
+ * fd, which must stay open: closing it drops the cache. Returns -EOPNOTSUPP
+ * if the working directory cannot back such a file, -1 on error.
+ */
+int alloc_pagecache(size_t size)
+{
+	struct statfs stfs;
+	char buf[4096];
+	size_t off;
+	int fd;
+
+	fd = open(".", O_TMPFILE | O_RDWR | O_EXCL, 0600);
+	if (fd < 0)
+		return errno == EOPNOTSUPP ? -EOPNOTSUPP : -1;
+	/* tmpfs hands out shmem pages, which are not reclaimable without swap */
+	if (fstatfs(fd, &stfs) || stfs.f_type == TMPFS_MAGIC) {
+		close(fd);
+		return -EOPNOTSUPP;
+	}
+	if (ftruncate(fd, size))
+		goto err;
+	for (off = 0; off < size; off += sizeof(buf))
+		if (read(fd, buf, sizeof(buf)) < 0)
+			goto err;
+	return fd;
+err:
+	close(fd);
+	return -1;
+}
+
 /**
  * setup_classid_environment() - Setup the cgroupv1 net_cls environment
  *
diff --git a/tools/testing/selftests/bpf/cgroup_helpers.h b/tools/testing/selftests/bpf/cgroup_helpers.h
index d42d2e13044e..6cc5ccb63fc2 100644
--- a/tools/testing/selftests/bpf/cgroup_helpers.h
+++ b/tools/testing/selftests/bpf/cgroup_helpers.h
@@ -20,6 +20,7 @@ int read_cgroup_file(const char *relative_path, const char *file,
 int read_cgroup_file_parent(const char *relative_path, const char *file,
 			    char *buf, size_t len);
 int cgroup_setup_and_join(const char *relative_path);
+int alloc_pagecache(size_t size);
 int get_root_cgroup(void);
 int create_and_get_cgroup(const char *relative_path);
 void remove_cgroup(const char *relative_path);
diff --git a/tools/testing/selftests/bpf/prog_tests/arena_memcg.c b/tools/testing/selftests/bpf/prog_tests/arena_memcg.c
index c76a7eb2f01d..55c8db956ff3 100644
--- a/tools/testing/selftests/bpf/prog_tests/arena_memcg.c
+++ b/tools/testing/selftests/bpf/prog_tests/arena_memcg.c
@@ -2,8 +2,6 @@
 #define _GNU_SOURCE
 #include <test_progs.h>
 #include <fcntl.h>
-#include <linux/magic.h>
-#include <sys/vfs.h>
 #include <sys/wait.h>
 #include <unistd.h>
 #include <sys/user.h>
@@ -37,38 +35,6 @@ static void dump_memcg(void)
 		fprintf(stderr, "memory.events:\n%s", buf);
 }
 
-/*
- * Fill the page cache with @size bytes of clean, reclaimable pages by
- * reading a sparse temp file, the way the cgroup selftests do. Returns the
- * fd, which must stay open: closing it drops the cache. Returns -EOPNOTSUPP
- * if the working directory cannot back such a file, -1 on error.
- */
-static int alloc_pagecache(size_t size)
-{
-	struct statfs stfs;
-	char buf[4096];
-	size_t off;
-	int fd;
-
-	fd = open(".", O_TMPFILE | O_RDWR | O_EXCL, 0600);
-	if (fd < 0)
-		return errno == EOPNOTSUPP ? -EOPNOTSUPP : -1;
-	/* tmpfs hands out shmem pages, which are not reclaimable without swap */
-	if (fstatfs(fd, &stfs) || stfs.f_type == TMPFS_MAGIC) {
-		close(fd);
-		return -EOPNOTSUPP;
-	}
-	if (ftruncate(fd, size))
-		goto err;
-	for (off = 0; off < size; off += sizeof(buf))
-		if (read(fd, buf, sizeof(buf)) < 0)
-			goto err;
-	return fd;
-err:
-	close(fd);
-	return -1;
-}
-
 void serial_test_arena_memcg(void)
 {
 	int cgroup_fd = -1, status, err;
-- 
2.56.0