s390/dasd/cio: Interpret ccw_device_get_mdc return value correctly (dd4b3c83) · Commits · 戴 / test

The max data count (mdc) is an unsigned 16-bit integer value as per AR documentation and is received via ccw_device_get_mdc() for a specific path mask from the CIO layer. The function itself also always returns a positive mdc value or 0 in case mdc isn't supported or couldn't be determined. Though, the comment for this function describes a negative return value to indicate failures. As a result, the DASD device driver interprets the return value of ccw_device_get_mdc() incorrectly. The error case is essentially a dead code path. To fix this behaviour, check explicitly for a return value of 0 and change the comment for ccw_device_get_mdc() accordingly. This fix merely enables the error code path in the DASD functions get_fcx_max_data() and verify_fcx_max_data(). The actual functionality stays the same and is still correct. Reviewed-by:

Cornelia Huck <cohuck@redhat.com> Signed-off-by:

Jan Höppner <hoeppner@linux.ibm.com> Acked-by:

Peter Oberparleiter <oberpar@linux.ibm.com> Reviewed-by:

Stefan Haberland <sth@linux.ibm.com> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

drivers/s390/block/dasd_eckd.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -1128,7 +1128,8 @@ static u32 get_fcx_max_data(struct dasd_device *device)
		{
		struct dasd_eckd_private *private = device->private;
		int fcx_in_css, fcx_in_gneq, fcx_in_features;
		int tpm, mdc;
		unsigned int mdc;
		int tpm;

		if (dasd_nofcx)
		return 0;
		@@ -1142,7 +1143,7 @@ static u32 get_fcx_max_data(struct dasd_device *device)
		return 0;

		mdc = ccw_device_get_mdc(device->cdev, 0);
		if (mdc < 0) {
		if (mdc == 0) {
		dev_warn(&device->cdev->dev, "Detecting the maximum supported data size for zHPF requests failed\n");
		return 0;
		} else {
		@@ -1153,12 +1154,12 @@ static u32 get_fcx_max_data(struct dasd_device *device)
		static int verify_fcx_max_data(struct dasd_device *device, __u8 lpm)
		{
		struct dasd_eckd_private *private = device->private;
		int mdc;
		unsigned int mdc;
		u32 fcx_max_data;

		if (private->fcx_max_data) {
		mdc = ccw_device_get_mdc(device->cdev, lpm);
		if ((mdc < 0)) {
		if (mdc == 0) {
		dev_warn(&device->cdev->dev,
		"Detecting the maximum data size for zHPF "
		"requests failed (rc=%d) for a new path %x\n",

drivers/s390/cio/device_ops.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -635,7 +635,7 @@ EXPORT_SYMBOL(ccw_device_tm_start_timeout);
		* @mask: mask of paths to use
		*
		* Return the number of 64K-bytes blocks all paths at least support
		* for a transport command. Return values <= 0 indicate failures.
		* for a transport command. Return value 0 indicates failure.
		*/
		int ccw_device_get_mdc(struct ccw_device *cdev, u8 mask)
		{

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