lib: add igt_debugfs_read()

A helpful function for when you want to read a whole debugfs file to a
string and don't want to worry about opening and closing file
descriptors and asserting buffer sizes.

We've been using this already for kms_frontbuffer_tracking and
kms_fbcon_fbt, so the only test with new code here is kms_fbc_crc.

Also notice that for kms_fbc_crc we had to increase the buffer size
since the file can sometimes be bigger than 64 bytes - depending on
the reason why FBC is disabled.

Of course, there are probably many other programs we can patch, but
I'm not doing this now.

v2: Add the macro to wrap sizeof() (Daniel).
v3: Add documentation for the macro too (Daniel).

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

lib/igt_debugfs.c

@@ -185,6 +185,33 @@ FILE *igt_debugfs_fopen(const char *filename,
 	return fopen(buf, mode);
 }
 
+/**
+ * __igt_debugfs_read:
+ * @filename: file name
+ * @buf: buffer where the contents will be stored, allocated by the caller
+ * @buf_size: size of the buffer
+ *
+ * This function opens the debugfs file, reads it, stores the content in the
+ * provided buffer, then closes the file. Users should make sure that the buffer
+ * provided is big enough to fit the whole file, plus one byte.
+ */
+void __igt_debugfs_read(const char *filename, char *buf, int buf_size)
+{
+	FILE *file;
+	size_t n_read;
+
+	file = igt_debugfs_fopen(filename, "r");
+	igt_assert(file);
+
+	n_read = fread(buf, 1, buf_size - 1, file);
+	igt_assert(n_read > 0);
+	igt_assert(feof(file));
+
+	buf[n_read] = '\0';
+
+	igt_assert(fclose(file) == 0);
+}
+
 /*
  * Pipe CRC
  */

lib/igt_debugfs.h

@@ -34,6 +34,18 @@ enum pipe;
 int igt_debugfs_open(const char *filename, int mode);
 FILE *igt_debugfs_fopen(const char *filename,
 			const char *mode);
+void __igt_debugfs_read(const char *filename, char *buf, int buf_size);
+
+/**
+ * igt_debugfs_read:
+ * @filename: name of the debugfs file
+ * @buf: buffer where the contents will be stored, allocated by the caller.
+ *
+ * This is just a convenience wrapper for __igt_debugfs_read. See its
+ * documentation.
+ */
+#define igt_debugfs_read(filename, buf) \
+		__igt_debugfs_read((filename), (buf), sizeof(buf))
 
 /*
  * Pipe CRC

tests/kms_fbc_crc.c

@@ -215,14 +215,9 @@ static void fill_mmap_gtt(data_t *data, uint32_t handle, unsigned char color)
 
 static bool fbc_enabled(data_t *data)
 {
-	FILE *status;
+	char str[128] = {};
-	char str[64] = {};
 
-	status = igt_debugfs_fopen("i915_fbc_status", "r");
+	igt_debugfs_read("i915_fbc_status", str);
-	igt_assert(status);
-
-	igt_assert(fread(str, 1, sizeof(str) - 1, status) > 0);
-	fclose(status);
 	return strstr(str, "FBC enabled") != NULL;
 }
 
@@ -544,8 +539,7 @@ igt_main
 	igt_skip_on_simulation();
 
 	igt_fixture {
-		char buf[64];
+		char buf[128];
-		FILE *status;
 
 		data.drm_fd = drm_open_any_master();
 		kmstest_set_vt_graphics_mode();
@@ -554,11 +548,7 @@ igt_main
 
 		igt_require_pipe_crc();
 
-		status = igt_debugfs_fopen("i915_fbc_status", "r");
+		igt_debugfs_read("i915_fbc_status", buf);
-		igt_require_f(status, "No i915_fbc_status found\n");
-		igt_assert_lt(0, fread(buf, 1, sizeof(buf), status));
-		fclose(status);
-		buf[sizeof(buf) - 1] = '\0';
 		igt_require_f(!strstr(buf, "unsupported on this chipset"),
 			      "FBC not supported\n");
 

tests/kms_fbcon_fbt.c

@@ -86,28 +86,11 @@ static void teardown_drm(struct drm_info *drm)
 	igt_assert(close(drm->fd) == 0);
 }
 
-static void debugfs_read(const char *filename, char *buf, int buf_size)
-{
-	FILE *file;
-	size_t n_read;
-
-	file = igt_debugfs_fopen(filename, "r");
-	igt_assert(file);
-
-	n_read = fread(buf, 1, buf_size - 1, file);
-	igt_assert(n_read > 0);
-	igt_assert(feof(file));
-
-	buf[n_read] = '\0';
-
-	igt_assert(fclose(file) == 0);
-}
-
 static bool fbc_supported_on_chipset(void)
 {
 	char buf[128];
 
-	debugfs_read("i915_fbc_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_fbc_status", buf);
 	return !strstr(buf, "FBC unsupported on this chipset\n");
 }
 
@@ -120,7 +103,7 @@ static bool fbc_is_enabled(void)
 {
 	char buf[128];
 
-	debugfs_read("i915_fbc_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_fbc_status", buf);
 	return strstr(buf, "FBC enabled\n");
 }
 
@@ -172,7 +155,7 @@ static bool psr_supported_on_chipset(void)
 {
 	char buf[256];
 
-	debugfs_read("i915_edp_psr_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_edp_psr_status", buf);
 	return strstr(buf, "Sink_Support: yes\n");
 }
 
@@ -185,7 +168,7 @@ static bool psr_is_enabled(void)
 {
 	char buf[256];
 
-	debugfs_read("i915_edp_psr_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_edp_psr_status", buf);
 	return strstr(buf, "\nActive: yes\n");
 }
 

tests/kms_frontbuffer_tracking.c

@@ -556,28 +556,11 @@ static bool set_mode_for_params(struct modeset_params *params)
 	return (rc == 0);
 }
 
-static void debugfs_read(const char *filename, char *buf, int buf_size)
-{
-	FILE *file;
-	size_t n_read;
-
-	file = igt_debugfs_fopen(filename, "r");
-	igt_assert(file);
-
-	n_read = fread(buf, 1, buf_size - 1, file);
-	igt_assert(n_read > 0);
-	igt_assert(feof(file));
-
-	buf[n_read] = '\0';
-
-	igt_assert(fclose(file) == 0);
-}
-
 static bool fbc_is_enabled(void)
 {
 	char buf[128];
 
-	debugfs_read("i915_fbc_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_fbc_status", buf);
 	return strstr(buf, "FBC enabled\n");
 }
 
@@ -585,7 +568,7 @@ static bool psr_is_enabled(void)
 {
 	char buf[256];
 
-	debugfs_read("i915_edp_psr_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_edp_psr_status", buf);
 	return (strstr(buf, "\nActive: yes\n"));
 }
 
@@ -596,7 +579,7 @@ static struct timespec fbc_get_last_action(void)
 	char *action;
 	ssize_t n_read;
 
-	debugfs_read("i915_fbc_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_fbc_status", buf);
 
 	action = strstr(buf, "\nLast action:");
 	igt_assert(action);
@@ -645,7 +628,7 @@ static void fbc_setup_last_action(void)
 	char buf[128];
 	char *action;
 
-	debugfs_read("i915_fbc_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_fbc_status", buf);
 
 	action = strstr(buf, "\nLast action:");
 	if (!action) {
@@ -664,7 +647,7 @@ static bool fbc_is_compressing(void)
 {
 	char buf[128];
 
-	debugfs_read("i915_fbc_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_fbc_status", buf);
 	return strstr(buf, "\nCompressing: yes\n") != NULL;
 }
 
@@ -677,7 +660,7 @@ static void fbc_setup_compressing(void)
 {
 	char buf[128];
 
-	debugfs_read("i915_fbc_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_fbc_status", buf);
 
 	if (strstr(buf, "\nCompressing:"))
 		fbc.supports_compressing = true;
@@ -1205,7 +1188,7 @@ static bool fbc_supported_on_chipset(void)
 {
 	char buf[128];
 
-	debugfs_read("i915_fbc_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_fbc_status", buf);
 	return !strstr(buf, "FBC unsupported on this chipset\n");
 }
 
@@ -1229,7 +1212,7 @@ static bool psr_sink_has_support(void)
 {
 	char buf[256];
 
-	debugfs_read("i915_edp_psr_status", buf, ARRAY_SIZE(buf));
+	igt_debugfs_read("i915_edp_psr_status", buf);
 	return strstr(buf, "Sink_Support: yes\n");
 }