[PATCH] fixup! libfile: implement read_fd counterpart to read_file

[Ahmad Fatoum]

- Justify why the buffer is three bytes longer than the file's content
  (Yann)
- Check for malloc failure (Yann)
- Don't close file descriptor on failure as it's opened outside
  the function
- set errno to indicate why the function failed

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 lib/libfile.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/lib/libfile.c b/lib/libfile.c
index c257baaa2733..a7762ab833f6 100644
--- a/lib/libfile.c
+++ b/lib/libfile.c
@@ -314,7 +314,9 @@ EXPORT_SYMBOL(read_file);
  * This function reads a file descriptor from offset 0 until EOF to an
  * allocated buffer.
  *
- * Return: The buffer containing the file or NULL on failure
+ * Return: On success, returns a nul-terminated buffer with the file's
+ * contents that should be deallocated with free().
+ * On error, NULL is returned and errno is set to an error code.
  */
 void *read_fd(int fd, size_t *out_size)
 {
@@ -329,24 +331,33 @@ void *read_fd(int fd, size_t *out_size)
 		off = lseek(fd, SEEK_SET, 0);
 	}
 	if (off < 0) {
-		ret = off;
-		goto close_fd;
+		errno = -off;
+		return NULL;
 	}
 
+	/* For user convenience, we always nul-terminate the buffer in
+	 * case it contains a string. As we don't want to assume the string
+	 * to be either an array of char or wchar_t, we just unconditionally
+	 * add 2 bytes as terminator. As the two byte terminator needs to be
+	 * aligned, we just make it three bytes
+	 */
 	buf = malloc(size + 3);
+	if (!buf) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
 	ret = read_full(fd, buf, size);
 	if (ret < 0) {
 		free(buf);
-		goto close_fd;
+		errno = -ret;
+		return NULL;
 	}
 
-	memset(&buf[size], '\0', 3);
+	memset(buf + size, '\0', 3);
 	*out_size = size;
 
-close_fd:
-	close(fd);
-
-	return ret < 0 ? NULL : buf;
+	return buf;
 }
 EXPORT_SYMBOL(read_fd);
 
-- 
2.39.2