linux-kernel - [PATCH 1/5] KVM: selftests: Extract guts of THP accessor to standalone sysfs helpers

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Message-ID: <20250327012350.1135621-2-jthoughton@google.com>
Date: Thu, 27 Mar 2025 01:23:46 +0000
From: James Houghton <jthoughton@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org
Cc: Maxim Levitsky <mlevitsk@...hat.com>, Axel Rasmussen <axelrasmussen@...gle.com>, 
	Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, mkoutny@...e.com, 
	Yu Zhao <yuzhao@...gle.com>, James Houghton <jthoughton@...gle.com>, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/5] KVM: selftests: Extract guts of THP accessor to
 standalone sysfs helpers

From: Sean Christopherson <seanjc@...gle.com>

Extract the guts of thp_configured() and get_trans_hugepagesz() to
standalone helpers so that the core logic can be reused for other sysfs
files, e.g. to query numa_balancing.

Opportunistically assert that the initial fscanf() read at least one byte,
and add a comment explaining the second call to fscanf().

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: James Houghton <jthoughton@...gle.com>
---
 tools/testing/selftests/kvm/lib/test_util.c | 35 ++++++++++++++-------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
index 8ed0b74ae8373..3dc8538f5d696 100644
--- a/tools/testing/selftests/kvm/lib/test_util.c
+++ b/tools/testing/selftests/kvm/lib/test_util.c
@@ -132,37 +132,50 @@ void print_skip(const char *fmt, ...)
 	puts(", skipping test");
 }
 
-bool thp_configured(void)
+static bool test_sysfs_path(const char *path)
 {
-	int ret;
 	struct stat statbuf;
+	int ret;
 
-	ret = stat("/sys/kernel/mm/transparent_hugepage", &statbuf);
+	ret = stat(path, &statbuf);
 	TEST_ASSERT(ret == 0 || (ret == -1 && errno == ENOENT),
-		    "Error in stating /sys/kernel/mm/transparent_hugepage");
+		    "Error in stat()ing '%s'", path);
 
 	return ret == 0;
 }
 
-size_t get_trans_hugepagesz(void)
+bool thp_configured(void)
+{
+	return test_sysfs_path("/sys/kernel/mm/transparent_hugepage");
+}
+
+static size_t get_sysfs_val(const char *path)
 {
 	size_t size;
 	FILE *f;
 	int ret;
 
-	TEST_ASSERT(thp_configured(), "THP is not configured in host kernel");
-
-	f = fopen("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size", "r");
-	TEST_ASSERT(f != NULL, "Error in opening transparent_hugepage/hpage_pmd_size");
+	f = fopen(path, "r");
+	TEST_ASSERT(f, "Error opening '%s'", path);
 
 	ret = fscanf(f, "%ld", &size);
+	TEST_ASSERT(ret > 0, "Error reading '%s'", path);
+
+	/* Re-scan the input stream to verify the entire file was read. */
 	ret = fscanf(f, "%ld", &size);
-	TEST_ASSERT(ret < 1, "Error reading transparent_hugepage/hpage_pmd_size");
-	fclose(f);
+	TEST_ASSERT(ret < 1, "Error reading '%s'", path);
 
+	fclose(f);
 	return size;
 }
 
+size_t get_trans_hugepagesz(void)
+{
+	TEST_ASSERT(thp_configured(), "THP is not configured in host kernel");
+
+	return get_sysfs_val("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size");
+}
+
 size_t get_def_hugetlb_pagesz(void)
 {
 	char buf[64];
-- 
2.49.0.395.g12beb8f557-goog