Add `patient_writev()` function

[lttng-ust.git] / snprintf / patient_write.c

diff --git a/snprintf/patient_write.c b/snprintf/patient_write.c
index 9bd2913f58ecbed3a9e56f4e6b5481d974f1d9d6..aa59ba1457d92ece99df4ac4daa7acc001d31e12 100644 (file)
--- a/snprintf/patient_write.c
+++ b/snprintf/patient_write.c
@@ -22,6 +22,9 @@
 /* write() */
 #include <unistd.h>
 
+/* writev() */
+#include <sys/uio.h>
+
 /* send() */
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -58,6 +61,52 @@ ssize_t patient_write(int fd, const void *buf, size_t count)
        return bufc-(const char *)buf;
 }
 
+/*
+ * The `struct iovec *iov` is not `const` because we modify it to support
+ * partial writes.
+ */
+ssize_t patient_writev(int fd, struct iovec *iov, int iovcnt)
+{
+       ssize_t written, total_written = 0;
+       int curr_element_idx = 0;
+
+       for(;;) {
+               written = writev(fd, iov + curr_element_idx,
+                               iovcnt - curr_element_idx);
+               if (written == -1 && errno == EINTR) {
+                       continue;
+               }
+               if (written <= 0) {
+                       return written;
+               }
+
+               total_written += written;
+
+               /*
+                * If it's not the last element in the vector and we have
+                * written more than the current element size, then increment
+                * the current element index until we reach the element that
+                * was partially written.
+                */
+               while (curr_element_idx < iovcnt &&
+                               written >= iov[curr_element_idx].iov_len) {
+                       written -= iov[curr_element_idx].iov_len;
+                       curr_element_idx++;
+               }
+
+               /* Maybe we are done. */
+               if (curr_element_idx >= iovcnt) {
+                       break;
+               }
+
+               /* Update the current element base and size. */
+               iov[curr_element_idx].iov_base += written;
+               iov[curr_element_idx].iov_len -= written;
+       }
+
+       return total_written;
+}
+
 ssize_t patient_send(int fd, const void *buf, size_t count, int flags)
 {
        const char *bufc = (const char *) buf;