aoe: user can ask driver to forget previously detected devices

When an AoE device is detected, the kernel is informed, and a new block device
is created. If the device is unused, the block device corresponding to remote
device that is no longer available may be removed from the system by telling
the aoe driver to "flush" its list of devices.

Without this patch, software like GPFS and LVM may attempt to read from AoE
devices that were discovered earlier but are no longer present, blocking until
the I/O attempt times out.

Signed-off-by: Ed L. Cashin <[e-mail]>
Cc: Greg KH <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/aoe/mkdevs.sh

···
 mknod -m 0200 $dir/interfaces c $MAJOR 4
 rm -f $dir/revalidate
 mknod -m 0200 $dir/revalidate c $MAJOR 5
+rm -f $dir/flush
+mknod -m 0200 $dir/flush c $MAJOR 6
 
 export n_partitions
 mkshelf=`echo $0 | sed 's!mkdevs!mkshelf!'`

Documentation/aoe/udev.txt

···
 SUBSYSTEM=="aoe", KERNEL=="err",	NAME="etherd/%k", GROUP="disk", MODE="0440"
 SUBSYSTEM=="aoe", KERNEL=="interfaces",	NAME="etherd/%k", GROUP="disk", MODE="0220"
 SUBSYSTEM=="aoe", KERNEL=="revalidate",	NAME="etherd/%k", GROUP="disk", MODE="0220"
+SUBSYSTEM=="aoe", KERNEL=="flush",	NAME="etherd/%k", GROUP="disk", MODE="0220"
 
 # aoe block devices     
 KERNEL=="etherd*",       NAME="%k", GROUP="disk"

drivers/block/aoe/aoe.h

···
 struct aoedev *aoedev_by_sysminor_m(ulong sysminor);
 void aoedev_downdev(struct aoedev *d);
 int aoedev_isbusy(struct aoedev *d);
+int aoedev_flush(const char __user *str, size_t size);
 
 int aoenet_init(void);
 void aoenet_exit(void);

drivers/block/aoe/aoechr.c

···
 	MINOR_DISCOVER,
 	MINOR_INTERFACES,
 	MINOR_REVALIDATE,
+	MINOR_FLUSH,
 	MSGSZ = 2048,
 	NMSG = 100,		/* message backlog to retain */
 };
···
 	{ MINOR_DISCOVER, "discover" },
 	{ MINOR_INTERFACES, "interfaces" },
 	{ MINOR_REVALIDATE, "revalidate" },
+	{ MINOR_FLUSH, "flush" },
 };
 
 static int
···
 		break;
 	case MINOR_REVALIDATE:
 		ret = revalidate(buf, cnt);
+		break;
+	case MINOR_FLUSH:
+		ret = aoedev_flush(buf, cnt);
 	}
 	if (ret == 0)
 		ret = cnt;

drivers/block/aoe/aoedev.c

···
 #include <linux/netdevice.h>
 #include "aoe.h"
 
+static void dummy_timer(ulong);
+static void aoedev_freedev(struct aoedev *);
+static void freetgt(struct aoetgt *t);
+
 static struct aoedev *devlist;
 static spinlock_t devlist_lock;
 
···
 	d->flags &= ~DEVFL_UP;
 }
 
+static void
+aoedev_freedev(struct aoedev *d)
+{
+	struct aoetgt **t, **e;
+
+	if (d->gd) {
+		aoedisk_rm_sysfs(d);
+		del_gendisk(d->gd);
+		put_disk(d->gd);
+	}
+	t = d->targets;
+	e = t + NTARGETS;
+	for (; t < e && *t; t++)
+		freetgt(*t);
+	if (d->bufpool)
+		mempool_destroy(d->bufpool);
+	kfree(d);
+}
+
+int
+aoedev_flush(const char __user *str, size_t cnt)
+{
+	ulong flags;
+	struct aoedev *d, **dd;
+	struct aoedev *rmd = NULL;
+	char buf[16];
+	int all = 0;
+
+	if (cnt >= 3) {
+		if (cnt > sizeof buf)
+			cnt = sizeof buf;
+		if (copy_from_user(buf, str, cnt))
+			return -EFAULT;
+		all = !strncmp(buf, "all", 3);
+	}
+
+	flush_scheduled_work();
+	spin_lock_irqsave(&devlist_lock, flags);
+	dd = &devlist;
+	while ((d = *dd)) {
+		spin_lock(&d->lock);
+		if ((!all && (d->flags & DEVFL_UP))
+		|| (d->flags & (DEVFL_GDALLOC|DEVFL_NEWSIZE))
+		|| d->nopen) {
+			spin_unlock(&d->lock);
+			dd = &d->next;
+			continue;
+		}
+		*dd = d->next;
+		aoedev_downdev(d);
+		d->flags |= DEVFL_TKILL;
+		spin_unlock(&d->lock);
+		d->next = rmd;
+		rmd = d;
+	}
+	spin_unlock_irqrestore(&devlist_lock, flags);
+	while ((d = rmd)) {
+		rmd = d->next;
+		del_timer_sync(&d->timer);
+		aoedev_freedev(d);	/* must be able to sleep */
+	}
+	return 0;
+}
+
 /* find it or malloc it */
 struct aoedev *
 aoedev_by_sysminor_m(ulong sysminor)
···
 	}
 	kfree(t->frames);
 	kfree(t);
-}
-
-static void
-aoedev_freedev(struct aoedev *d)
-{
-	struct aoetgt **t, **e;
-
-	if (d->gd) {
-		aoedisk_rm_sysfs(d);
-		del_gendisk(d->gd);
-		put_disk(d->gd);
-	}
-	t = d->targets;
-	e = t + NTARGETS;
-	for (; t < e && *t; t++)
-		freetgt(*t);
-	if (d->bufpool)
-		mempool_destroy(d->bufpool);
-	kfree(d);
 }
 
 void