KVM: selftests: Use pread() to read binary stats header

Use pread() with an explicit offset when reading the header and the header
name for a binary stats fd so that the common helper and the binary stats
test don't subtly rely on the file effectively being untouched, e.g. to
allow multiple reads of the header, name, etc.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230711230131.648752-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
index 07732a157ccd640ccccdc73477f98ce796c33b46..eb1ff597bcca95801c25ee594d61592abd6dd5fa 100644 (file)
--- a/tools/testing/selftests/kvm/include/kvm_util_base.h
+++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
@@ -362,8 +362,10 @@ static inline void read_stats_header(int stats_fd, struct kvm_stats_header *head
 {
        ssize_t ret;
 
-       ret = read(stats_fd, header, sizeof(*header));
-       TEST_ASSERT(ret == sizeof(*header), "Read stats header");
+       ret = pread(stats_fd, header, sizeof(*header), 0);
+       TEST_ASSERT(ret == sizeof(*header),
+                   "Failed to read '%lu' header bytes, ret = '%ld'",
+                   sizeof(*header), ret);
 }
 
 struct kvm_stats_desc *read_stats_descriptors(int stats_fd,

diff --git a/tools/testing/selftests/kvm/kvm_binary_stats_test.c b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
index a7001e29dc06afbe88f0f62b9b9d4741782a3d96..eae99d0e8377a440b34e62dacd98c7455337c5bc 100644 (file)
--- a/tools/testing/selftests/kvm/kvm_binary_stats_test.c
+++ b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
@@ -43,8 +43,10 @@ static void stats_test(int stats_fd)
        id = malloc(header.name_size);
        TEST_ASSERT(id, "Allocate memory for id string");
 
-       ret = read(stats_fd, id, header.name_size);
-       TEST_ASSERT(ret == header.name_size, "Read id string");
+       ret = pread(stats_fd, id, header.name_size, sizeof(header));
+       TEST_ASSERT(ret == header.name_size,
+                   "Expected header size '%u', read '%lu' bytes",
+                   header.name_size, ret);
 
        /* Check id string, that should start with "kvm" */
        TEST_ASSERT(!strncmp(id, "kvm", 3) && strlen(id) < header.name_size,