From: Hans-Joachim Picht <hpicht@redhat.com>
Date: Tue, 14 Jul 2009 18:56:38 +0200
Subject: [s390] dasd: dev attr to disable blocking on lost paths
Message-id: 20090714165638.GB2417@blc4eb509856389.ibm.com
O-Subject: [RHEL5 U5 PATCH 1/1] s390 - dasd: add device attribute to disable blocking on lost paths
Bugzilla: 503222
RH-Acked-by: Pete Zaitcev <zaitcev@redhat.com>

Description
============
When the connection between host and storage server is lost, the
dasd device driver usually blocks all I/O on affected devices and
waits for them to reappear. In some setups however it would be
better if the I/O is returned as error so that device can be
recovered by some other means, eg. in a raid or multipath setup.

Solution: Add a new dasd feature 'failfast' which controls the dasd
driver handling of requests and can be configured per device
independently of the setting of the FAILFAST flag per request.
If the 'failfast' feature is enabled for a device, the dasd
driver will handle requests as if the request had the FAILFAST
flag set, particularly posting I/O failure, when no path is
operational to the device.
The 'failfast' feature can be configured via the new sysfs
attribute 'failfast' or via the 'dasd=' parameter, just like
any other feature. By default, the 'failfast' feature is not
set.

Bugzilla
=========

BZ 503222
https://bugzilla.redhat.com/show_bug.cgi?id=503222

Upstream status of the patch:
=============================

The patch is upstream as of kernel version 2.6.29

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=13de227bcd80fbdaeebe1f31154487dddb7d5b1e

Test status:
============

The patch has been tested and fixes the problem.
The fix has been verified by the IBM test department.

Please ACK.

With best regards,

	Hans

diff --git a/drivers/s390/block/dasd_devmap.c b/drivers/s390/block/dasd_devmap.c
index 293ef05..5b88b1d 100644
--- a/drivers/s390/block/dasd_devmap.c
+++ b/drivers/s390/block/dasd_devmap.c
@@ -204,6 +204,8 @@ dasd_feature_list(char *str, char **endp)
 			features |= DASD_FEATURE_USEDIAG;
 		else if (len == 6 && !strncmp(str, "erplog", 6))
 			features |= DASD_FEATURE_ERPLOG;
+		else if (len == 8 && !strncmp(str, "failfast", 8))
+			features |= DASD_FEATURE_FAILFAST;
 		else {
 			MESSAGE(KERN_WARNING,
 				"unsupported feature: %*s, "
@@ -661,6 +663,52 @@ dasd_device_from_cdev(struct ccw_device *cdev)
  */
 
 /*
+ * failfast controls the behaviour, if no path is available
+ */
+static ssize_t
+dasd_ff_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct dasd_devmap *devmap;
+	int ff_flag;
+
+	devmap = dasd_find_busid(dev->bus_id);
+	if (!IS_ERR(devmap))
+		ff_flag = (devmap->features & DASD_FEATURE_FAILFAST) != 0;
+	else
+		ff_flag = (DASD_FEATURE_DEFAULT & DASD_FEATURE_FAILFAST) != 0;
+	return snprintf(buf, PAGE_SIZE, ff_flag ? "1\n" : "0\n");
+}
+
+static ssize_t
+dasd_ff_store(struct device *dev, struct device_attribute *attr,
+	      const char *buf, size_t count)
+{
+	struct dasd_devmap *devmap;
+	int val;
+	char *endp;
+
+	devmap = dasd_devmap_from_cdev(to_ccwdev(dev));
+	if (IS_ERR(devmap))
+		return PTR_ERR(devmap);
+
+	val = simple_strtoul(buf, &endp, 0);
+	if (((endp + 1) < (buf + count)) || (val > 1))
+		return -EINVAL;
+
+	spin_lock(&dasd_devmap_lock);
+	if (val)
+		devmap->features |= DASD_FEATURE_FAILFAST;
+	else
+		devmap->features &= ~DASD_FEATURE_FAILFAST;
+	if (devmap->device)
+		devmap->device->features = devmap->features;
+	spin_unlock(&dasd_devmap_lock);
+	return count;
+}
+
+static DEVICE_ATTR(failfast, 0644, dasd_ff_show, dasd_ff_store);
+
+/*
  * readonly controls the readonly status of a dasd
  */
 static ssize_t
@@ -974,6 +1022,7 @@ static struct attribute * dasd_attrs[] = {
 	&dev_attr_use_diag.attr,
 	&dev_attr_eer_enabled.attr,
 	&dev_attr_erplog.attr,
+	&dev_attr_failfast.attr,
 	NULL,
 };
 
diff --git a/drivers/s390/block/dasd_diag.c b/drivers/s390/block/dasd_diag.c
index 63bd607..a919fed 100644
--- a/drivers/s390/block/dasd_diag.c
+++ b/drivers/s390/block/dasd_diag.c
@@ -548,7 +548,8 @@ dasd_diag_build_cp(struct dasd_device * device, struct request *req)
 	}
 	cqr->retries = DIAG_MAX_RETRIES;
 	cqr->buildclk = get_clock();
-	if (blk_noretry_ff_request(req))
+	if (blk_noretry_ff_request(req) ||
+	    device->features & DASD_FEATURE_FAILFAST)
 		set_bit(DASD_CQR_FLAGS_FAILFAST, &cqr->flags);
 	cqr->device = device;
 	cqr->expires = DIAG_TIMEOUT;
diff --git a/drivers/s390/block/dasd_eckd.c b/drivers/s390/block/dasd_eckd.c
index 79f33c5..5c22065 100644
--- a/drivers/s390/block/dasd_eckd.c
+++ b/drivers/s390/block/dasd_eckd.c
@@ -1410,7 +1410,8 @@ dasd_eckd_build_cp(struct dasd_device * device, struct request *req)
 			recid++;
 		}
 	}
-	if (blk_noretry_ff_request(req))
+	if (blk_noretry_ff_request(req) ||
+	    device->features & DASD_FEATURE_FAILFAST)
 		set_bit(DASD_CQR_FLAGS_FAILFAST, &cqr->flags);
 	cqr->device = device;
 	cqr->expires = 5 * 60 * HZ;	/* 5 minutes */
diff --git a/drivers/s390/block/dasd_fba.c b/drivers/s390/block/dasd_fba.c
index f4a1c28..7250144 100644
--- a/drivers/s390/block/dasd_fba.c
+++ b/drivers/s390/block/dasd_fba.c
@@ -344,7 +344,8 @@ dasd_fba_build_cp(struct dasd_device * device, struct request *req)
 			recid++;
 		}
 	}
-	if (blk_noretry_ff_request(req))
+	if (blk_noretry_ff_request(req) ||
+	    device->features & DASD_FEATURE_FAILFAST)
 		set_bit(DASD_CQR_FLAGS_FAILFAST, &cqr->flags);
 	cqr->device = device;
 	cqr->expires = 5 * 60 * HZ;	/* 5 minutes */
diff --git a/include/asm-s390/dasd.h b/include/asm-s390/dasd.h
index 1113967..eb602dc 100644
--- a/include/asm-s390/dasd.h
+++ b/include/asm-s390/dasd.h
@@ -77,6 +77,7 @@ typedef struct dasd_information2_t {
 #define DASD_FEATURE_USEDIAG	     0x02
 #define DASD_FEATURE_INITIAL_ONLINE  0x04
 #define DASD_FEATURE_ERPLOG	     0x08
+#define DASD_FEATURE_FAILFAST	     0x10
 
 #define DASD_PARTN_BITS 2