XListInputDevices: don't touch ndevices in case of error

We used to always set *ndevices to the number of devices returned by the
server. This magically worked because we pretty much never returned an error
except on faulty server or library implementations. With 19a9cd60 we now have
more chances of getting an error, so the polite thing is to just leave *ndevices
alone when we error out.

Document it as such in the man page, just in case someone accidentally reads
it.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
CC: Niels Ole Salscheider <niels_ole@salscheider-online.de>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>

2 files changed, 22 insertions, 11 deletions

diff --git a/man/XListInputDevices.txt b/man/XListInputDevices.txt
index 276660d..450f377 100644
--- a/man/XListInputDevices.txt
+++ b/man/XListInputDevices.txt
@@ -220,5 +220,13 @@ DESCRIPTION
    Floating. If the device is a master device, attached specifies
    the device ID of the master device this device is paired with.
 
-   To free the XDeviceInfo array created by XListInputDevices, use
-   XFreeDeviceList.
+RETURN VALUE
+------------
+
+   XListInputDevices returns a pointer to an array of XDeviceInfo
+   structs and sets ndevices_return to the number of elements in
+   that array. To free the XDeviceInfo array created by
+   XListInputDevices, use XFreeDeviceList.
+
+   On error, XListInputDevices returns NULL and ndevices_return is
+   left unmodified.
diff --git a/src/XListDev.c b/src/XListDev.c
index e4bd3d5..dda6011 100644
--- a/src/XListDev.c
+++ b/src/XListDev.c
@@ -175,7 +175,7 @@ ParseClassInfo(xAnyClassPtr *any, XAnyClassPtr *Any, int num_classes)
 XDeviceInfo *
 XListInputDevices(
     register Display	*dpy,
-    int			*ndevices)
+    int			*ndevices_return)
 {
     size_t s, size;
     xListInputDevicesReq *req;
@@ -190,6 +190,7 @@ XListInputDevices(
     int i;
     unsigned long rlen;
     XExtDisplayInfo *info = XInput_find_display(dpy);
+    int ndevices;
 
     LockDisplay(dpy);
     if (_XiCheckExtInit(dpy, XInput_Initial_Release, info) == -1)
@@ -205,8 +206,8 @@ XListInputDevices(
 	return (XDeviceInfo *) NULL;
     }
 
-    if ((*ndevices = rep.ndevices)) {	/* at least 1 input device */
-	size = *ndevices * sizeof(XDeviceInfo);
+    if ((ndevices = rep.ndevices)) {	/* at least 1 input device */
+	size = ndevices * sizeof(XDeviceInfo);
 	if (rep.length < (INT_MAX >> 2)) {
 	    rlen = rep.length << 2;	/* multiply length by 4    */
 	    slist = list = Xmalloc(rlen);
@@ -219,17 +220,17 @@ XListInputDevices(
 	}
 	_XRead(dpy, (char *)list, rlen);
 
-	any = (xAnyClassPtr) ((char *)list + (*ndevices * sizeof(xDeviceInfo)));
+	any = (xAnyClassPtr) ((char *)list + (ndevices * sizeof(xDeviceInfo)));
 	sav_any = any;
 	end = (char *)list + rlen;
-	for (i = 0; i < *ndevices; i++, list++) {
+	for (i = 0; i < ndevices; i++, list++) {
             if(SizeClassInfo(&any, end - (char *)any, (int)list->num_classes, &s))
                 goto out;
             size += s;
 	}
 
 	Nptr = ((unsigned char *)list) + rlen;
-	for (i = 0, nptr = (unsigned char *)any; i < *ndevices; i++) {
+	for (i = 0, nptr = (unsigned char *)any; i < ndevices; i++) {
 	    if (nptr >= Nptr)
 		goto out;
 	    size += *nptr + 1;
@@ -245,10 +246,10 @@ XListInputDevices(
 	}
 	sclist = clist;
 	Any = (XAnyClassPtr) ((char *)clist +
-			      (*ndevices * sizeof(XDeviceInfo)));
+			      (ndevices * sizeof(XDeviceInfo)));
 	list = slist;
 	any = sav_any;
-	for (i = 0; i < *ndevices; i++, list++, clist++) {
+	for (i = 0; i < ndevices; i++, list++, clist++) {
 	    clist->type = list->type;
 	    clist->id = list->id;
 	    clist->use = list->use;
@@ -261,7 +262,7 @@ XListInputDevices(
 	clist = sclist;
 	nptr = (unsigned char *)any;
 	Nptr = (unsigned char *)Any;
-	for (i = 0; i < *ndevices; i++, clist++) {
+	for (i = 0; i < ndevices; i++, clist++) {
 	    clist->name = (char *)Nptr;
 	    memcpy(Nptr, nptr + 1, *nptr);
 	    Nptr += (*nptr);
@@ -270,6 +271,8 @@ XListInputDevices(
 	}
     }
 
+    *ndevices_return = ndevices;
+
   out:
     XFree((char *)slist);
     UnlockDisplay(dpy);