Fix using zvol as slog device

During the original ZoL port the vdev_uses_zvols() function was
disabled until it could be properly implemented.  This prevented
a zpool from use a zvol for its slog device.

This patch implements that missing functionality by adding a
zvol_is_zvol() function to zvol.c.  Given the full path to a
device it will lookup the device and verify its major number
against the registered zvol major number for the system.  If
they match we know the device is a zvol.

Signed-off-by: Brian Behlendorf <[email protected]>
Closes #1131

1 files changed, 23 insertions, 0 deletions

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 5d4802560..7a448f194 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -141,6 +141,29 @@ zvol_find_by_name(const char *name)
 	return NULL;
 }
 
+
+/*
+ * Given a path, return TRUE if path is a ZVOL.
+ */
+boolean_t
+zvol_is_zvol(const char *device)
+{
+	struct block_device *bdev;
+	unsigned int major;
+
+	bdev = lookup_bdev(device);
+	if (IS_ERR(bdev))
+		return (B_FALSE);
+
+	major = MAJOR(bdev->bd_dev);
+	bdput(bdev);
+
+	if (major == zvol_major)
+            return (B_TRUE);
+
+	return (B_FALSE);
+}
+
 /*
  * ZFS_IOC_CREATE callback handles dmu zvol and zap object creation.
  */