KVM: selftests: Add helpers to read integer module params

Add helpers to read integer module params, which is painfully non-trivial
because the pain of dealing with strings in C is exacerbated by the kernel
inserting a newline.

Don't bother differentiating between int, uint, short, etc.  They all fit
in an int, and KVM (thankfully) doesn't have any integer params larger
than an int.

Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240109230250.424295-24-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

tools/testing/selftests/kvm/include/kvm_util_base.h

@@ -259,6 +259,10 @@ bool get_kvm_param_bool(const char *param);
 bool get_kvm_intel_param_bool(const char *param);
 bool get_kvm_amd_param_bool(const char *param);
 
+int get_kvm_param_integer(const char *param);
+int get_kvm_intel_param_integer(const char *param);
+int get_kvm_amd_param_integer(const char *param);
+
 unsigned int kvm_check_cap(long cap);
 
 static inline bool kvm_has_cap(long cap)

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -51,13 +51,13 @@ int open_kvm_dev_path_or_exit(void)
 	return _open_kvm_dev_path_or_exit(O_RDONLY);
 }
 
-static bool get_module_param_bool(const char *module_name, const char *param)
+static ssize_t get_module_param(const char *module_name, const char *param,
+				void *buffer, size_t buffer_size)
 {
 	const int path_size = 128;
 	char path[path_size];
-	char value;
-	ssize_t r;
-	int fd;
+	ssize_t bytes_read;
+	int fd, r;
 
 	r = snprintf(path, path_size, "/sys/module/%s/parameters/%s",
 		     module_name, param);
@@ -66,11 +66,46 @@ static bool get_module_param_bool(const char *module_name, const char *param)
 
 	fd = open_path_or_exit(path, O_RDONLY);
 
-	r = read(fd, &value, 1);
-	TEST_ASSERT(r == 1, "read(%s) failed", path);
+	bytes_read = read(fd, buffer, buffer_size);
+	TEST_ASSERT(bytes_read > 0, "read(%s) returned %ld, wanted %ld bytes",
+		    path, bytes_read, buffer_size);
 
 	r = close(fd);
 	TEST_ASSERT(!r, "close(%s) failed", path);
+	return bytes_read;
+}
+
+static int get_module_param_integer(const char *module_name, const char *param)
+{
+	/*
+	 * 16 bytes to hold a 64-bit value (1 byte per char), 1 byte for the
+	 * NUL char, and 1 byte because the kernel sucks and inserts a newline
+	 * at the end.
+	 */
+	char value[16 + 1 + 1];
+	ssize_t r;
+
+	memset(value, '\0', sizeof(value));
+
+	r = get_module_param(module_name, param, value, sizeof(value));
+	TEST_ASSERT(value[r - 1] == '\n',
+		    "Expected trailing newline, got char '%c'", value[r - 1]);
+
+	/*
+	 * Squash the newline, otherwise atoi_paranoid() will complain about
+	 * trailing non-NUL characters in the string.
+	 */
+	value[r - 1] = '\0';
+	return atoi_paranoid(value);
+}
+
+static bool get_module_param_bool(const char *module_name, const char *param)
+{
+	char value;
+	ssize_t r;
+
+	r = get_module_param(module_name, param, &value, sizeof(value));
+	TEST_ASSERT_EQ(r, 1);
 
 	if (value == 'Y')
 		return true;
@@ -95,6 +130,21 @@ bool get_kvm_amd_param_bool(const char *param)
 	return get_module_param_bool("kvm_amd", param);
 }
 
+int get_kvm_param_integer(const char *param)
+{
+	return get_module_param_integer("kvm", param);
+}
+
+int get_kvm_intel_param_integer(const char *param)
+{
+	return get_module_param_integer("kvm_intel", param);
+}
+
+int get_kvm_amd_param_integer(const char *param)
+{
+	return get_module_param_integer("kvm_amd", param);
+}
+
 /*
  * Capability
  *