iovec-util: rename iovec_increment() -> iovec_inc_many()

Also,
- use iovec_inc() in the loop,
- do not return true when input is NULL or all iovec are empty.

src/basic/iovec-util.c

@@ -30,29 +30,30 @@ size_t iovec_total_size(const struct iovec *iovec, size_t n) {
         return sum;
 }
 
-bool iovec_increment(struct iovec *iovec, size_t n, size_t k) {
+bool iovec_inc_many(struct iovec *iovec, size_t n, size_t k) {
         assert(iovec || n == 0);
 
         /* Returns true if there is nothing else to send (bytes written cover all of the iovec),
          * false if there's still work to do. */
 
+        bool have = false;
         FOREACH_ARRAY(j, iovec, n) {
-                size_t sub;
-
                 if (j->iov_len == 0)
                         continue;
                 if (k == 0)
                         return false;
 
-                sub = MIN(j->iov_len, k);
-                j->iov_len -= sub;
-                j->iov_base = (uint8_t*) j->iov_base + sub;
+                size_t sub = MIN(j->iov_len, k);
+                iovec_inc(j, sub);
                 k -= sub;
+
+                have = have || iovec_is_set(j);
         }
 
         assert(k == 0); /* Anything else would mean that we wrote more bytes than available,
                          * or the kernel reported writing more bytes than sent. */
-        return true;
+
+        return !have;
 }
 
 struct iovec* iovec_make_string(struct iovec *iovec, const char *s) {

src/basic/iovec-util.h

@@ -11,7 +11,7 @@ extern const struct iovec iovec_empty;    /* Points to an empty, but valid (i.e.
 
 size_t iovec_total_size(const struct iovec *iovec, size_t n) _nonnull_if_nonzero_(1, 2);
 
-bool iovec_increment(struct iovec *iovec, size_t n, size_t k) _nonnull_if_nonzero_(1, 2);
+bool iovec_inc_many(struct iovec *iovec, size_t n, size_t k) _nonnull_if_nonzero_(1, 2);
 
 struct iovec* iovec_make_string(struct iovec *iovec, const char *s);
 

src/basic/log.c

@@ -557,7 +557,7 @@ static int write_to_syslog(
                 if (!syslog_is_stream)
                         break;
 
-                if (iovec_increment(iovec, ELEMENTSOF(iovec), n))
+                if (iovec_inc_many(iovec, ELEMENTSOF(iovec), n))
                         break;
         }