[SCSI] scsi_host_lookup: error returns and NULL pointers

This patch cleans up the behavior of scsi_host_lookup().

The original implementation attempted to use the dual role of
either returning a pointer value, or a negative error code.
User's needed to use IS_ERR() to check the result. Additionally,
the IS_ERR() macro never checks for when a NULL pointer was
returned, so a NULL pointer actually passes with a success case.
Note: scsi_host_get(), used by scsi_host_lookup(), can return
a NULL pointer.

Talk about a mudhole for the unitiated to step into....

This patch converts scsi_host_lookup() to return either NULL
or a valid pointer. The consumers were updated for the change.
Signed-off-by: James Smart <james.smart@emulex.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/hosts.c

@@ -464,7 +464,7 @@ static int __scsi_host_match(struct device *dev, void *data)
 struct Scsi_Host *scsi_host_lookup(unsigned short hostnum)
 {
 	struct device *cdev;
-	struct Scsi_Host *shost = ERR_PTR(-ENXIO);
+	struct Scsi_Host *shost = NULL;
 
 	cdev = class_find_device(&shost_class, NULL, &hostnum,
 				 __scsi_host_match);

drivers/scsi/scsi_proc.c

@@ -259,8 +259,8 @@ static int scsi_add_single_device(uint host, uint channel, uint id, uint lun)
 	int error = -ENXIO;
 
 	shost = scsi_host_lookup(host);
-	if (IS_ERR(shost))
-		return PTR_ERR(shost);
+	if (!shost)
+		return error;
 
 	if (shost->transportt->user_scan)
 		error = shost->transportt->user_scan(shost, channel, id, lun);
@@ -287,8 +287,8 @@ static int scsi_remove_single_device(uint host, uint channel, uint id, uint lun)
 	int error = -ENXIO;
 
 	shost = scsi_host_lookup(host);
-	if (IS_ERR(shost))
-		return PTR_ERR(shost);
+	if (!shost)
+		return error;
 	sdev = scsi_device_lookup(shost, channel, id, lun);
 	if (sdev) {
 		scsi_remove_device(sdev);

drivers/scsi/scsi_tgt_lib.c

@@ -460,7 +460,7 @@ int scsi_tgt_kspace_exec(int host_no, u64 itn_id, int result, u64 tag,
 
 	/* TODO: replace with a O(1) alg */
 	shost = scsi_host_lookup(host_no);
-	if (IS_ERR(shost)) {
+	if (!shost) {
 		printk(KERN_ERR "Could not find host no %d\n", host_no);
 		return -EINVAL;
 	}
@@ -550,7 +550,7 @@ int scsi_tgt_kspace_tsk_mgmt(int host_no, u64 itn_id, u64 mid, int result)
 	dprintk("%d %d %llx\n", host_no, result, (unsigned long long) mid);
 
 	shost = scsi_host_lookup(host_no);
-	if (IS_ERR(shost)) {
+	if (!shost) {
 		printk(KERN_ERR "Could not find host no %d\n", host_no);
 		return err;
 	}
@@ -603,7 +603,7 @@ int scsi_tgt_kspace_it_nexus_rsp(int host_no, u64 itn_id, int result)
 	dprintk("%d %d%llx\n", host_no, result, (unsigned long long)itn_id);
 
 	shost = scsi_host_lookup(host_no);
-	if (IS_ERR(shost)) {
+	if (!shost) {
 		printk(KERN_ERR "Could not find host no %d\n", host_no);
 		return err;
 	}

drivers/scsi/scsi_transport_iscsi.c

@@ -1361,7 +1361,7 @@ iscsi_tgt_dscvr(struct iscsi_transport *transport,
 		return -EINVAL;
 
 	shost = scsi_host_lookup(ev->u.tgt_dscvr.host_no);
-	if (IS_ERR(shost)) {
+	if (!shost) {
 		printk(KERN_ERR "target discovery could not find host no %u\n",
 		       ev->u.tgt_dscvr.host_no);
 		return -ENODEV;
@@ -1387,7 +1387,7 @@ iscsi_set_host_param(struct iscsi_transport *transport,
 		return -ENOSYS;
 
 	shost = scsi_host_lookup(ev->u.set_host_param.host_no);
-	if (IS_ERR(shost)) {
+	if (!shost) {
 		printk(KERN_ERR "set_host_param could not find host no %u\n",
 		       ev->u.set_host_param.host_no);
 		return -ENODEV;