Add a safe wrapper for write and fix some warnings

1. Add a function writeall and make swrite wrap that function. Use either writeall or swrite, depending on whether we want to exit on errors or not.
2. Fix warnings when compiling with a higher optimisation level.
(CFLAGS ?= -pipe -O3 -march=native -mtune=native -freorder-blocks-and-partition)

Signed-off-by: hwangcc <hwangcc@csie.nctu.edu.tw>

libi3/safewrappers.c

@@ -8,8 +8,10 @@
 #include <string.h>
 #include <stdlib.h>
 #include <stdarg.h>
+#include <unistd.h>
 #include <stdio.h>
 #include <err.h>
+#include <errno.h>
 
 #include "libi3.h"
 
@@ -56,3 +58,30 @@ int sasprintf(char **strp, const char *fmt, ...) {
     va_end(args);
     return result;
 }
+
+ssize_t writeall(int fd, const void *buf, size_t count) {
+    int written = 0;
+    ssize_t n = 0;
+
+    while (written < count) {
+        n = write(fd, buf + written, count - written);
+        if (n == -1) {
+            if (errno == EINTR || errno == EAGAIN)
+                continue;
+            return n;
+        }
+        written += n;
+    }
+
+    return written;
+}
+
+ssize_t swrite(int fd, const void *buf, size_t count) {
+    ssize_t n;
+
+    n = writeall(fd, buf, count);
+    if (n == -1)
+        err(EXIT_FAILURE, "Failed to write %d", fd);
+    else
+        return n;
+}