From: David van Moolenbroek <david@minix3.org>
Date: Fri, 24 Jul 2015 20:54:27 +0000 (+0000)
Subject: LOG: fix bugs in userland write handler
X-Git-Url: http://zhaoyanbai.com/repos/%22http:/www.isc.org/icons/zpipe.c?a=commitdiff_plain;h=818c405ae139c2477c949f24c5ba13747095f5bb;p=minix.git

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 caba7cf3d..ee4393a7b 100644
--- 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;
 }
 
 /*===========================================================================*