LOG: fix bugs in userland write handler

- report correct number of bytes written;
- correctly return partial writes on failure;
- do not overwrite result if there is a pending read.

Change-Id: I92aeeaee1eccb47c2aa2b6666a2f560c3cb17f42

diff --git a/minix/drivers/system/log/log.c b/minix/drivers/system/log/log.c
index caba7cf3d372d7d64c46d887019e1dd39728e42c..ee4393a7badd4c3fdbcbf2cef83259504bc3e0e3 100644 (file)
--- a/minix/drivers/system/log/log.c
+++ b/minix/drivers/system/log/log.c
@@ -126,7 +126,7 @@ subwrite(struct logdevice *log, size_t size, endpoint_t endpt,
        cp_grant_id_t grant, char *localbuf)
 {
   size_t count, offset;
-  int overflow, r;
+  int overflow, r, result;
   devminor_t minor;
   char *buf;
   message m;
@@ -134,6 +134,7 @@ subwrite(struct logdevice *log, size_t size, endpoint_t endpt,
   /* With a sufficiently large input size, we might wrap around the ring buffer
    * multiple times.
    */
+  result = 0;
   for (offset = 0; offset < size; offset += count) {
        count = size - offset;
 
@@ -147,8 +148,11 @@ subwrite(struct logdevice *log, size_t size, endpoint_t endpt,
        }
        else {
                if((r=sys_safecopyfrom(endpt, grant, offset,
-                       (vir_bytes)buf, count)) != OK)
-                       break; /* do process partial write upon error */
+                       (vir_bytes)buf, count)) != OK) {
+                       /* return any partial success upon error */
+                       result = (offset > 0) ? (int)offset : r;
+                       break;
+               }
        }
 
        LOGINC(log->log_write, count);
@@ -160,7 +164,7 @@ subwrite(struct logdevice *log, size_t size, endpoint_t endpt,
                LOGINC(log->log_read, overflow);
         }
 
-       r = offset; /* this will be the return value upon success */
+       result += (int)count;
   }
 
   if (log->log_size > 0 && log->log_source != NONE) {
@@ -185,7 +189,7 @@ subwrite(struct logdevice *log, size_t size, endpoint_t endpt,
        log->log_selected &= ~CDEV_OP_RD;
   }
 
-  return r;
+  return result;
 }
 
 /*===========================================================================*