[PATCH] usb: fastboot: increase max answer size to 256

[Sascha Hauer <s.hauer@pengutronix.de>]

Initial fasboot specification allowed at maximum 64 characters as
answer. This has been increased to 256 [1]. Allow for longer answer
sizes.

While at it use a define for the maximum answer length to avoid
repeating the hardcoded number. Also allow the answer to be exactly
the maximum length. Previous implementation used a 64 byte string
which included the '\0' string end and limited the usable size to
63 bytes. Now we can use the full 256 bytes.

[1] https://android.googlesource.com/platform/system/core/+/master/fastboot/

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 common/fastboot.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/common/fastboot.c b/common/fastboot.c
index b661d610a3..96d7fbd8c7 100644
--- a/common/fastboot.c
+++ b/common/fastboot.c
@@ -269,11 +269,13 @@ static char *fastboot_msg[] = {
 	[FASTBOOT_MSG_NONE] = "",
 };
 
+#define FASTBOOT_MAX_RESPONSE_SIZE 256
+
 int fastboot_tx_print(struct fastboot *fb, enum fastboot_msg_type type,
 		      const char *fmt, ...)
 {
 	struct va_format vaf;
-	char buf[64];
+	char buf[FASTBOOT_MAX_RESPONSE_SIZE + 1];
 	va_list ap;
 	int n;
 	const char *msg = fastboot_msg[type];
@@ -282,7 +284,7 @@ int fastboot_tx_print(struct fastboot *fb, enum fastboot_msg_type type,
 	vaf.fmt = fmt;
 	vaf.va = &ap;
 
-	n = snprintf(buf, 64, "%s%pV", msg, &vaf);
+	n = snprintf(buf, FASTBOOT_MAX_RESPONSE_SIZE + 1, "%s%pV", msg, &vaf);
 
 	switch (type) {
 	case FASTBOOT_MSG_OKAY:
@@ -302,8 +304,8 @@ int fastboot_tx_print(struct fastboot *fb, enum fastboot_msg_type type,
 
 	va_end(ap);
 
-	if (n > 64)
-		n = 64;
+	if (n > FASTBOOT_MAX_RESPONSE_SIZE)
+		n = FASTBOOT_MAX_RESPONSE_SIZE;
 
 	return fb->write(fb, buf, n);
 }
-- 
2.47.3