Windows: Retry open_device if it fails with ERROR_ACCESS_DENIED

[pqu]

Windows opens system mice/keyboards for exclusive access. They can still be sent feature reports, but neither read nor write access can be requested when the handle is opened.

• http://msdn.microsoft.com/en-us/library/ff543477.aspx
• http://www.lvr.com/hidfaq.htm

[pqu]

Done. I swapped the semantics of the parameter so there wasn't a strange double-negative like no_readwrite == FALSE.

[signal11]

Can you combine these patches so they are one patch?

Use git rebase -i and git push (you'll need to do --force, but it's ok since I haven't pulled from you yet, unless someone else is tracking this branch, in which case put it on a separate branch for me).

Thanks!

Alan.

[cactrot]

On my windows 8 64bit machine instead of ERROR_ACCESS_DENIED I get ERROR_SHARING_VIOLATION. I'm trying to open a Audio Class device that, like keyboards and mice, windows claims read and write access too.
It seems to open if I use this condition:
(dev->device_handle == INVALID_HANDLE_VALUE &&
( GetLastError() == ERROR_ACCESS_DENIED || GetLastError() == ERROR_SHARING_VIOLATION ) )

I believe the firmware on the device already has a feature report for remote wakeup and stall endpoint but so far all my attempts to get or send a feature report result in "Incorrect function".

What I want to do is add a couple of feature reports to communicate with the device while still using it as a windows sound device.

[signal11]

Your audio software probably has the device open already.

I'm not sure what you mean by "if I use this condition." Can you explain further or post a patch snippet?

[cactrot]

I'm a little new to github, hopefully this is the preferred way to link in a patch.

https://gist.github.com/cactrot/7242364

I know windows has the device open for read and write as a system audio device. I have read several places that it is still possible to send feature reports if you don't request read/write access. I have DSP chip from TI ( C5535 ) and I want to use it as a USB sound card but I also want to be able to control the DSP from an application. I'm not sure of the "Incorrect function" means the report has been sent and the device is not responding or if windows is giving the error. I suppose that is mostly what I need to figure out at the moment.

[z3ntu]

EDIT: You should rather use #335

Rebased patch (makes my application able to send/receive feature reports on Windows):

(also adjusted the link in the commit message to archive.org as the link is dead)

From 61e8072d6f81504b1834c085328f10c7b6a5aadd Mon Sep 17 00:00:00 2001
From: philip <p@partylemon.com>
Date: Thu, 8 Mar 2012 16:12:52 +1300
Subject: [PATCH] Windows: Retry open_device if it fails with
 ERROR_ACCESS_DENIED.

    (Ref. "Why do I receive 'Access denied' when attempting to access my HID?"
           http://web.archive.org/web/20130317064425/http://www.lvr.com/hidfaq.htm)

Swap semantics on open_device()'s second parameter to make sense with new usage.
---
 windows/hid.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/windows/hid.c b/windows/hid.c
index 86810d7..d7aa0d2 100755
--- a/windows/hid.c
+++ b/windows/hid.c
@@ -225,11 +225,13 @@ static int lookup_functions()
 }
 #endif
 
-static HANDLE open_device(const char *path, BOOL enumerate)
+static HANDLE open_device(const char *path, BOOL request_rw)
 {
 	HANDLE handle;
-	DWORD desired_access = (enumerate)? 0: (GENERIC_WRITE | GENERIC_READ);
-	DWORD share_mode = FILE_SHARE_READ|FILE_SHARE_WRITE;
+	DWORD desired_access = (request_rw)?(GENERIC_WRITE|GENERIC_READ):0;
+	DWORD share_mode = (request_rw)?
+							FILE_SHARE_READ:
+							FILE_SHARE_READ|FILE_SHARE_WRITE;
 
 	handle = CreateFileA(path,
 		desired_access,
@@ -370,7 +372,7 @@ struct hid_device_info HID_API_EXPORT * HID_API_CALL hid_enumerate(unsigned shor
 		//wprintf(L"HandleName: %s\n", device_interface_detail_data->DevicePath);
 
 		/* Open a handle to the device */
-		write_handle = open_device(device_interface_detail_data->DevicePath, TRUE);
+		write_handle = open_device(device_interface_detail_data->DevicePath, FALSE);
 
 		/* Check validity of write_handle. */
 		if (write_handle == INVALID_HANDLE_VALUE) {
@@ -566,7 +568,15 @@ HID_API_EXPORT hid_device * HID_API_CALL hid_open_path(const char *path)
 	dev = new_hid_device();
 
 	/* Open a handle to the device */
-	dev->device_handle = open_device(path, FALSE);
+	dev->device_handle = open_device(path, TRUE);
+
+	/* If the device is a system keyboard/mouse, Windows (2k+) takes exclusive
+	   read/write access. Feature reports can still be sent, but only if
+	   neither read nor write access is requested. */
+	if (dev->device_handle == INVALID_HANDLE_VALUE &&
+		GetLastError() == ERROR_ACCESS_DENIED) {
+		dev->device_handle = open_device(path, FALSE);
+	}
 
 	/* Check validity of write_handle. */
 	if (dev->device_handle == INVALID_HANDLE_VALUE) {
-- 
2.21.0