From 03fb60893cf59e16f26d1f6d84b8a4921bbe8eae Mon Sep 17 00:00:00 2001
From: Francis Deslauriers <francis.deslauriers@efficios.com>
Date: Fri, 3 May 2019 15:11:00 -0400
Subject: [PATCH] common: add bt_common_read() function
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This function wraps the `read()` function to handle EINTR and partial
reads.

It returns the `count` value on success, or a smaller value than `count`
on error.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: Ib0385855447200d97a58da704dcf68423e857033
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1248
Reviewed-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---
 include/babeltrace/common-internal.h | 52 +++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/include/babeltrace/common-internal.h b/include/babeltrace/common-internal.h
index 0e84e8fa..19594fe3 100644
--- a/include/babeltrace/common-internal.h
+++ b/include/babeltrace/common-internal.h
@@ -32,9 +32,10 @@
 #include <babeltrace/trace-ir/event-class-const.h>
 #include <babeltrace/graph/self-message-iterator.h>
 #include <babeltrace/value.h>
-#include <stdarg.h>
 #include <inttypes.h>
+#include <stdarg.h>
 #include <stdint.h>
+#include <unistd.h>
 #include <glib.h>
 
 #define BT_COMMON_COLOR_RESET              "\033[0m"
@@ -305,6 +306,55 @@ void bt_common_custom_snprintf(char *buf, size_t buf_size,
 BT_HIDDEN
 size_t bt_common_get_page_size(void);
 
+/*
+ * Wraps read() function to handle EINTR and partial reads.
+ * On success, it returns `count` received as parameter. On error, it returns a
+ * value smaller than the requested `count`.
+ */
+static inline
+ssize_t bt_common_read(int fd, void *buf, size_t count)
+{
+	size_t i = 0;
+	ssize_t ret;
+
+	BT_ASSERT(buf);
+
+	/* Never return an overflow value. */
+	BT_ASSERT(count <= SSIZE_MAX);
+
+	do {
+		ret = read(fd, buf + i, count - i);
+		if (ret < 0) {
+			if (errno == EINTR) {
+#ifdef BT_LOGD_STR
+				BT_LOGD_STR("read() call interrupted. Retrying...");
+#endif
+				/* retry operation */
+				continue;
+			} else {
+#ifdef BT_LOGE_ERRNO
+				BT_LOGE_ERRNO("Error while reading", ": fd=%d",
+					fd);
+#endif
+				goto end;
+			}
+		}
+		i += ret;
+		BT_ASSERT(i <= count);
+	} while (count - i > 0 && ret > 0);
+
+end:
+	if (ret >= 0) {
+		if (i == 0) {
+			ret = -1;
+		} else {
+			ret = i;
+		}
+	}
+
+	return ret;
+}
+
 static inline
 const char *bt_common_field_class_type_string(enum bt_field_class_type class_type)
 {
-- 
2.34.1