tracing: Add full state to trace_seq

The trace_seq buffer might fill up, and right now one needs to check the
return value of each printf into the buffer to check for that.

Instead, have the buffer keep track of whether it is full or not, and
reject more input if it is full or would have overflowed with an input
that wasn't added.

Cc: Lai Jiangshan <[e-mail]>
Signed-off-by: Johannes Berg <[e-mail]>
Signed-off-by: Steven Rostedt <[e-mail]>

include/linux/trace_seq.h

···
 	unsigned char		buffer[PAGE_SIZE];
 	unsigned int		len;
 	unsigned int		readpos;
+	int			full;
 };
 
 static inline void
···
 {
 	s->len = 0;
 	s->readpos = 0;
+	s->full = 0;
 }
 
 /*

kernel/trace/trace_output.c

···
 	va_list ap;
 	int ret;
 
-	if (!len)
+	if (s->full || !len)
 		return 0;
 
 	va_start(ap, fmt);
···
 	va_end(ap);
 
 	/* If we can't write it all, don't bother writing anything */
-	if (ret >= len)
+	if (ret >= len) {
+		s->full = 1;
 		return 0;
+	}
 
 	s->len += ret;
 
···
 	int len = (PAGE_SIZE - 1) - s->len;
 	int ret;
 
-	if (!len)
+	if (s->full || !len)
 		return 0;
 
 	ret = vsnprintf(s->buffer + s->len, len, fmt, args);
 
 	/* If we can't write it all, don't bother writing anything */
-	if (ret >= len)
+	if (ret >= len) {
+		s->full = 1;
 		return 0;
+	}
 
 	s->len += ret;
 
···
 	int len = (PAGE_SIZE - 1) - s->len;
 	int ret;
 
-	if (!len)
+	if (s->full || !len)
 		return 0;
 
 	ret = bstr_printf(s->buffer + s->len, len, fmt, binary);
 
 	/* If we can't write it all, don't bother writing anything */
-	if (ret >= len)
+	if (ret >= len) {
+		s->full = 1;
 		return 0;
+	}
 
 	s->len += ret;
 
···
 {
 	int len = strlen(str);
 
-	if (len > ((PAGE_SIZE - 1) - s->len))
+	if (s->full)
 		return 0;
+
+	if (len > ((PAGE_SIZE - 1) - s->len)) {
+		s->full = 1;
+		return 0;
+	}
 
 	memcpy(s->buffer + s->len, str, len);
 	s->len += len;
···
 
 int trace_seq_putc(struct trace_seq *s, unsigned char c)
 {
-	if (s->len >= (PAGE_SIZE - 1))
+	if (s->full)
 		return 0;
+
+	if (s->len >= (PAGE_SIZE - 1)) {
+		s->full = 1;
+		return 0;
+	}
 
 	s->buffer[s->len++] = c;
 
···
 
 int trace_seq_putmem(struct trace_seq *s, const void *mem, size_t len)
 {
-	if (len > ((PAGE_SIZE - 1) - s->len))
+	if (s->full)
 		return 0;
+
+	if (len > ((PAGE_SIZE - 1) - s->len)) {
+		s->full = 1;
+		return 0;
+	}
 
 	memcpy(s->buffer + s->len, mem, len);
 	s->len += len;
···
 	unsigned char hex[HEX_CHARS];
 	const unsigned char *data = mem;
 	int i, j;
+
+	if (s->full)
+		return 0;
 
 #ifdef __BIG_ENDIAN
 	for (i = 0, j = 0; i < len; i++) {
···
 {
 	void *ret;
 
-	if (len > ((PAGE_SIZE - 1) - s->len))
+	if (s->full)
+		return 0;
+
+	if (len > ((PAGE_SIZE - 1) - s->len)) {
+		s->full = 1;
 		return NULL;
+	}
 
 	ret = s->buffer + s->len;
 	s->len += len;
···
 {
 	unsigned char *p;
 
-	if (s->len >= (PAGE_SIZE - 1))
+	if (s->full)
 		return 0;
+
+	if (s->len >= (PAGE_SIZE - 1)) {
+		s->full = 1;
+		return 0;
+	}
+
 	p = d_path(path, s->buffer + s->len, PAGE_SIZE - s->len);
 	if (!IS_ERR(p)) {
 		p = mangle_path(s->buffer + s->len, p, "\n");
···
 		return 1;
 	}
 
+	s->full = 1;
 	return 0;
 }
 
···
 	struct file *file = NULL;
 	unsigned long vmstart = 0;
 	int ret = 1;
+
+	if (s->full)
+		return 0;
 
 	if (mm) {
 		const struct vm_area_struct *vma;