sys/vfs: add vfs_write_iol()

sys/include/vfs.h

@@ -68,6 +68,7 @@
 
 #include "sched.h"
 #include "clist.h"
+#include "iolist.h"
 #include "mtd.h"
 #include "xfa.h"
 
@@ -809,6 +810,17 @@ ssize_t vfs_read(int fd, void *dest, size_t count);
  */
 ssize_t vfs_write(int fd, const void *src, size_t count);
 
+/**
+ * @brief Write bytes from an iolist to an open file
+ *
+ * @param[in]  fd       fd number obtained from vfs_open
+ * @param[in]  iolist   iolist to read from
+ *
+ * @return number of bytes written on success
+ * @return <0 on error
+ */
+ssize_t vfs_write_iol(int fd, const iolist_t *iolist);
+
 /**
  * @brief Synchronize a file on storage
  *        Any pending writes are written out to storage.

sys/vfs/vfs.c

@@ -355,6 +355,22 @@ ssize_t vfs_write(int fd, const void *src, size_t count)
     return filp->f_op->write(filp, src, count);
 }
 
+ssize_t vfs_write_iol(int fd, const iolist_t *snips)
+{
+    int res, sum = 0;
+
+    while (snips) {
+        res = vfs_write(fd, snips->iol_base, snips->iol_len);
+        if (res < 0) {
+            return res;
+        }
+        sum += res;
+        snips = snips->iol_next;
+    }
+
+    return sum;
+}
+
 int vfs_fsync(int fd)
 {
     DEBUG_NOT_STDOUT(fd, "vfs_fsync: %d\n", fd);