The previous code had a bug that would add a trailing null byte to
the returned descriptor.
Signed-off-by: George Spelvin <linux@xxxxxxxxxxx>
---
I gave up on rebooting my primary desktop where I discovered the problem
and tested the patch on a different machine. I came up with another
way to simplify the ascii2desc code. It's perhaps a bit tricky, but
it's small.
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 95ccfa0..34de475 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -337,72 +337,89 @@ static const u8 ss_rh_config_descriptor[] = {
/*-------------------------------------------------------------------------*/
-/*
- * helper routine for returning string descriptors in UTF-16LE
- * input can actually be ISO-8859-1; ASCII is its 7-bit subset
+/**
+ * ascii2desc() - Helper routine for producing UTF-16LE string descriptors
+ * @s: Null-terminated ASCII (actually ISO-8859-1) string
+ * @buf: Buffer for USB string descriptor (header + UTF-16LE)
+ * @len: Length (in bytes; may be odd) of descriptor buffer.
+ *
+ * The return value is the number of bytes filled in: 2 + 2*strlen(s) or
+ * buflen, whichever is less.
+ *
+ * USB String descriptors can contain at most 126 characters; input
+ * strings longer than that are truncated.
*/
-static unsigned ascii2utf(char *s, u8 *utf, int utfmax)
+static unsigned
+ascii2desc(char const *s, u8 *buf, unsigned len)
{
- unsigned retval;
+ unsigned n, t = 2 + 2*strlen(s);
- for (retval = 0; *s && utfmax > 1; utfmax -= 2, retval += 2) {
- *utf++ = *s++;
- *utf++ = 0;
- }
- if (utfmax > 0) {
- *utf = *s;
- ++retval;
+ if (t > 254)
+ t = 254; /* Longest possible UTF string descriptor */
+ if (len > t)
+ len = t;
+
+ t += USB_DT_STRING << 8; /* Now t is first 16 bits to store */
+
+ n = len;
+ while (n--) {
+ *buf++ = t;
+ if (!n--)
+ break;
+ *buf++ = t >> 8;
+ t = (unsigned char)*s++;
}
- return retval;
+ return len;
}
-/*
- * rh_string - provides manufacturer, product and serial strings for root hub
- * @id: the string ID number (1: serial number, 2: product, 3: vendor)
+/**
+ * rh_string() - provides string descriptors for root hub
+ * @id: the string ID number (0: langids, 1: serial #, 2: product, 3: vendor)
* @hcd: the host controller for this root hub
- * @data: return packet in UTF-16 LE
- * @len: length of the return packet
+ * @data: buffer for output packet
+ * @len: length of the provided buffer
*
* Produces either a manufacturer, product or serial number string for the
* virtual root hub device.
+ * Returns the number of bytes filled in: the length of the descriptor or
+ * of the provided buffer, whichever is less.
*/
-static unsigned rh_string(int id, struct usb_hcd *hcd, u8 *data, unsigned len)
+static unsigned
+rh_string(int id, struct usb_hcd const *hcd, u8 *data, unsigned len)
{
- char buf [100];
+ char buf[100];
+ char const *s;
+ static char const langids[4] = {4, USB_DT_STRING, 0x09, 0x04};
// language ids
- if (id == 0) {
- buf[0] = 4; buf[1] = 3; /* 4 bytes string data */
- buf[2] = 0x09; buf[3] = 0x04; /* MSFT-speak for "en-us" */
- len = min_t(unsigned, len, 4);
- memcpy (data, buf, len);
+ switch (id) {
+ case 0:
+ /* Array of LANGID codes (0x0409 is MSFT-speak for "en-us") */
+ /* See http://www.usb.org/developers/docs/USB_LANGIDs.pdf */
+ if (len > 4)
+ len = 4;
+ memcpy(data, langids, len);
return len;
-
- // serial number
- } else if (id == 1) {
- strlcpy (buf, hcd->self.bus_name, sizeof buf);
-
- // product description
- } else if (id == 2) {
- strlcpy (buf, hcd->product_desc, sizeof buf);
-
- // id 3 == vendor description
- } else if (id == 3) {
+ case 1:
+ /* Serial number */
+ s = hcd->self.bus_name;
+ break;
+ case 2:
+ /* Product name */
+ s = hcd->product_desc;
+ break;
+ case 3:
+ /* Manufacturer */
snprintf (buf, sizeof buf, "%s %s %s", init_utsname()->sysname,
init_utsname()->release, hcd->driver->description);
- }
-
- switch (len) { /* All cases fall through */
+ s = buf;
+ break;
default:
- len = 2 + ascii2utf (buf, data + 2, len - 2);
- case 2:
- data [1] = 3; /* type == string */
- case 1:
- data [0] = 2 * (strlen (buf) + 1);
- case 0:
- ; /* Compiler wants a statement here */
+ /* Can't happen; caller guarantees it */
+ return 0;
}
- return len;
+
+ return ascii2desc(s, data, len);
}
--
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