btrfs: plumb fs_info into btrfs_work

In order to provide an fsid for trace events, we'll need a btrfs_fs_info
pointer.  The most lightweight way to do that for btrfs_work structures
is to associate it with the __btrfs_workqueue structure.  Each queued
btrfs_work structure has a workqueue associated with it, so that's
a natural fit.  It's a privately defined structures, so we add accessors
to retrieve the fs_info pointer.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 4956562..cb6d13c 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2310,17 +2310,19 @@
 	unsigned int flags = WQ_MEM_RECLAIM | WQ_FREEZABLE | WQ_UNBOUND;
 
 	fs_info->workers =
-		btrfs_alloc_workqueue("worker", flags | WQ_HIGHPRI,
-				      max_active, 16);
+		btrfs_alloc_workqueue(fs_info, "worker",
+				      flags | WQ_HIGHPRI, max_active, 16);
 
 	fs_info->delalloc_workers =
-		btrfs_alloc_workqueue("delalloc", flags, max_active, 2);
+		btrfs_alloc_workqueue(fs_info, "delalloc",
+				      flags, max_active, 2);
 
 	fs_info->flush_workers =
-		btrfs_alloc_workqueue("flush_delalloc", flags, max_active, 0);
+		btrfs_alloc_workqueue(fs_info, "flush_delalloc",
+				      flags, max_active, 0);
 
 	fs_info->caching_workers =
-		btrfs_alloc_workqueue("cache", flags, max_active, 0);
+		btrfs_alloc_workqueue(fs_info, "cache", flags, max_active, 0);
 
 	/*
 	 * a higher idle thresh on the submit workers makes it much more
@@ -2328,41 +2330,48 @@
 	 * devices
 	 */
 	fs_info->submit_workers =
-		btrfs_alloc_workqueue("submit", flags,
+		btrfs_alloc_workqueue(fs_info, "submit", flags,
 				      min_t(u64, fs_devices->num_devices,
 					    max_active), 64);
 
 	fs_info->fixup_workers =
-		btrfs_alloc_workqueue("fixup", flags, 1, 0);
+		btrfs_alloc_workqueue(fs_info, "fixup", flags, 1, 0);
 
 	/*
 	 * endios are largely parallel and should have a very
 	 * low idle thresh
 	 */
 	fs_info->endio_workers =
-		btrfs_alloc_workqueue("endio", flags, max_active, 4);
+		btrfs_alloc_workqueue(fs_info, "endio", flags, max_active, 4);
 	fs_info->endio_meta_workers =
-		btrfs_alloc_workqueue("endio-meta", flags, max_active, 4);
+		btrfs_alloc_workqueue(fs_info, "endio-meta", flags,
+				      max_active, 4);
 	fs_info->endio_meta_write_workers =
-		btrfs_alloc_workqueue("endio-meta-write", flags, max_active, 2);
+		btrfs_alloc_workqueue(fs_info, "endio-meta-write", flags,
+				      max_active, 2);
 	fs_info->endio_raid56_workers =
-		btrfs_alloc_workqueue("endio-raid56", flags, max_active, 4);
+		btrfs_alloc_workqueue(fs_info, "endio-raid56", flags,
+				      max_active, 4);
 	fs_info->endio_repair_workers =
-		btrfs_alloc_workqueue("endio-repair", flags, 1, 0);
+		btrfs_alloc_workqueue(fs_info, "endio-repair", flags, 1, 0);
 	fs_info->rmw_workers =
-		btrfs_alloc_workqueue("rmw", flags, max_active, 2);
+		btrfs_alloc_workqueue(fs_info, "rmw", flags, max_active, 2);
 	fs_info->endio_write_workers =
-		btrfs_alloc_workqueue("endio-write", flags, max_active, 2);
+		btrfs_alloc_workqueue(fs_info, "endio-write", flags,
+				      max_active, 2);
 	fs_info->endio_freespace_worker =
-		btrfs_alloc_workqueue("freespace-write", flags, max_active, 0);
+		btrfs_alloc_workqueue(fs_info, "freespace-write", flags,
+				      max_active, 0);
 	fs_info->delayed_workers =
-		btrfs_alloc_workqueue("delayed-meta", flags, max_active, 0);
+		btrfs_alloc_workqueue(fs_info, "delayed-meta", flags,
+				      max_active, 0);
 	fs_info->readahead_workers =
-		btrfs_alloc_workqueue("readahead", flags, max_active, 2);
+		btrfs_alloc_workqueue(fs_info, "readahead", flags,
+				      max_active, 2);
 	fs_info->qgroup_rescan_workers =
-		btrfs_alloc_workqueue("qgroup-rescan", flags, 1, 0);
+		btrfs_alloc_workqueue(fs_info, "qgroup-rescan", flags, 1, 0);
 	fs_info->extent_workers =
-		btrfs_alloc_workqueue("extent-refs", flags,
+		btrfs_alloc_workqueue(fs_info, "extent-refs", flags,
 				      min_t(u64, fs_devices->num_devices,
 					    max_active), 8);