Introduce the read_into_buffer helper

This will be required for page-cache and page-proxy set.

Signed-off-by: Rodrigo Bruno <rbruno at gsd.inesc-id.pt>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/util.h

@@ -267,6 +267,7 @@ FILE *fopenat(int dirfd, char *path, char *cflags);
 void split(char *str, char token, char ***out, int *n);
 
 int fd_has_data(int lfd);
+size_t read_into_buffer(int fd, char *buff, size_t size);
 
 int make_yard(char *path);
 

util.c

@@ -872,6 +872,21 @@ int fd_has_data(int lfd)
 	return ret;
 }
 
+size_t read_into_buffer(int fd, char *buff, size_t size)
+{
+	size_t n = 0;
+	size_t curr = 0;
+
+	while (1) {
+		n  = read(fd, buff + curr, size - curr);
+		if (n < 1)
+			return n;
+		curr += n;
+		if (curr == size)
+			return size;
+	}
+}
+
 int make_yard(char *path)
 {
 	if (mount("none", path, "tmpfs", 0, NULL)) {