[LTP] [PATCH 1/2] lib: safe_file_ops: Add SAFE_FILE_READ_STR()

[Cyril Hrubis]

Unlike the scanf("%s") this function can properly handle empty files and
in case of an empty file produces an empty string.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
---
 include/tst_safe_file_ops.h | 21 +++++++++++++++++++++
 lib/safe_file_ops.c         | 24 ++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/include/tst_safe_file_ops.h b/include/tst_safe_file_ops.h
index 0d8819594..d9110ba9c 100644
--- a/include/tst_safe_file_ops.h
+++ b/include/tst_safe_file_ops.h
@@ -14,6 +14,27 @@
 	safe_file_scanf(__FILE__, __LINE__, NULL, \
 	                (path), (fmt), ## __VA_ARGS__)
 
+/**
+ * SAFE_FILE_READ_STR() - Reads a string from a file.
+ *
+ * Unlike scanf("%s") this function works fine with empty files or files that
+ * consist only of white spaces. In such case an empty string is stored into
+ * the supplied buffer.
+ *
+ * It's recomended to use this for various sysfs or procfs files that may be
+ * empty.
+ *
+ * @path: A path to a file.
+ * @buf: A buffer to store the string into.
+ * @buf_size: A buffer size.
+ */
+#define SAFE_FILE_READ_STR(path, buf, buf_size) \
+	safe_file_read_str(__FILE__, __LINE__, \
+	                   (path), (buf), (buf_size))
+
+void safe_file_read_str(const char *file, const int lineno,
+                        const char *path, char *buf, size_t buf_size);
+
 #define FILE_LINES_SCANF(path, fmt, ...) \
 	file_lines_scanf(__FILE__, __LINE__, NULL, 0,\
 			(path), (fmt), ## __VA_ARGS__)
diff --git a/lib/safe_file_ops.c b/lib/safe_file_ops.c
index 8314c4b1b..2d163c0af 100644
--- a/lib/safe_file_ops.c
+++ b/lib/safe_file_ops.c
@@ -160,6 +160,30 @@ void safe_file_scanf(const char *file, const int lineno,
 	}
 }
 
+void safe_file_read_str(const char *file, const int lineno,
+                        const char *path, char *buf, size_t buf_size)
+{
+	FILE *f;
+
+	f = fopen(path, "r");
+	if (!f) {
+		tst_brkm_(file, lineno, TBROK | TERRNO, NULL,
+		          "Failed to open FILE '%s' for reading", path);
+	}
+
+	if (!fgets(buf, buf_size, f))
+		buf[0] = 0;
+
+	size_t len = strlen(buf);
+
+	if (len && buf[len-1] == '\n')
+		buf[len-1] = 0;
+
+	if (fclose(f)) {
+		tst_brkm_(file, lineno, TBROK | TERRNO, NULL,
+			"Failed to close FILE '%s'", path);
+	}
+}
 
 /*
  * Try to parse each line from file specified by 'path' according
-- 
2.52.0