perf tools: Add filename__read_str util function

Adding filename__read_str util function to read
text file and return it in the char array.

The interface is:
int filename__read_str(const char *filename, char **buf, size_t *sizep)

Returns 0/-1 if the read suceeded/fail respectively.

buf - place to store the data pointer
size - place to store data size

v2 change:
- better error handling suggested by Namhyung Kim.

Signed-off-by: Jiri Olsa <[e-mail]>
Cc: Corey Ashford <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/util.c

···
 #endif
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <errno.h>
 #include <linux/kernel.h>
 
 /*
···
 		*value = atoi(line);
 		err = 0;
 	}
+
+	close(fd);
+	return err;
+}
+
+int filename__read_str(const char *filename, char **buf, size_t *sizep)
+{
+	size_t size = 0, alloc_size = 0;
+	void *bf = NULL, *nbf;
+	int fd, n, err = 0;
+
+	fd = open(filename, O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	do {
+		if (size == alloc_size) {
+			alloc_size += BUFSIZ;
+			nbf = realloc(bf, alloc_size);
+			if (!nbf) {
+				err = -ENOMEM;
+				break;
+			}
+
+			bf = nbf;
+		}
+
+		n = read(fd, bf + size, alloc_size - size);
+		if (n < 0) {
+			if (size) {
+				pr_warning("read failed %d: %s\n",
+					   errno, strerror(errno));
+				err = 0;
+			} else
+				err = -errno;
+
+			break;
+		}
+
+		size += n;
+	} while (n > 0);
+
+	if (!err) {
+		*sizep = size;
+		*buf   = bf;
+	} else
+		free(bf);
 
 	close(fd);
 	return err;

tools/perf/util/util.h

···
 void free_srcline(char *srcline);
 
 int filename__read_int(const char *filename, int *value);
+int filename__read_str(const char *filename, char **buf, size_t *sizep);
 #endif /* GIT_COMPAT_UTIL_H */