[PATCH 10/26] dynamic_debug: enlarge command/query write buffer

[jim.cromie@gmail.com]

From: Jim Cromie <jim.cromie@gmail.com>

Current write buffer is 256 bytes, on stack.  Allocate it off heap,
and enlarge it to 4096 bytes, big enough for ~100 queries (at 40 bytes
each), and error out if not.  This should be enough for most uses, and
others can be split into 2 writes.

This makes it play nicely with:
 $> cat debug-queries-file > /dbg/dynamic_debug/control

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 lib/dynamic_debug.c |   16 ++++++++++++----
 1 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 4bf27f3..2b3393f 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -590,24 +590,32 @@ __setup("ddebug_query=", ddebug_setup_query);
  * File_ops->write method for <debugfs>/dynamic_debug/conrol.  Gathers the
  * command text from userspace, parses and executes it.
  */
+#define USER_BUF_PAGE 4095
 static ssize_t ddebug_proc_write(struct file *file, const char __user *ubuf,
 				  size_t len, loff_t *offp)
 {
-	char tmpbuf[256];
+	char *tmpbuf;
 	int ret;
 
 	if (len == 0)
 		return 0;
-	/* we don't check *offp -- multiple writes() are allowed */
-	if (len > sizeof(tmpbuf)-1)
+	if (len > USER_BUF_PAGE - 1) {
+		pr_warn("expected <%d bytes into control \n", USER_BUF_PAGE);
 		return -E2BIG;
-	if (copy_from_user(tmpbuf, ubuf, len))
+	}
+	tmpbuf = kmalloc(len + 1, GFP_KERNEL);
+	if (!tmpbuf)
+		return -ENOMEM;
+	if (copy_from_user(tmpbuf, ubuf, len)) {
+		kfree(tmpbuf);
 		return -EFAULT;
+	}
 	tmpbuf[len] = '\0';
 	if (verbose)
 		pr_info("read %d bytes from userspace\n", (int)len);
 
 	ret = ddebug_exec_queries(tmpbuf);
+	kfree(tmpbuf);
 	if (ret)
 		return ret;
 
-- 
1.7.4.4