Btrfs: add DEVICE_READY ioctl

This will be used in conjunction with btrfs device ready <dev>.  This is
needed for initrd's to have a nice and lightweight way to tell if all of the
devices needed for a file system are in the cache currently.  This keeps
them from having to do mount+sleep loops waiting for devices to show up.
Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

4 files changed, 18 insertions, 2 deletions

diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index 021c55ed8aed..4e3e5d342a2b 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -363,7 +363,8 @@ struct btrfs_ioctl_get_dev_stats {
                                         struct btrfs_ioctl_ino_path_args)
 #define BTRFS_IOC_LOGICAL_INO _IOWR(BTRFS_IOCTL_MAGIC, 36, \
                                         struct btrfs_ioctl_ino_path_args)
+#define BTRFS_IOC_DEVICES_READY _IOR(BTRFS_IOCTL_MAGIC, 39, \
+                                     struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
                                       struct btrfs_ioctl_get_dev_stats)
-
 #endif
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 88a2d2bb2d75..26da344231ac 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1462,6 +1462,13 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
                 ret = btrfs_scan_one_device(vol->name, FMODE_READ,
                                             &btrfs_fs_type, &fs_devices);
                 break;
+        case BTRFS_IOC_DEVICES_READY:
+                ret = btrfs_scan_one_device(vol->name, FMODE_READ,
+                                            &btrfs_fs_type, &fs_devices);
+                if (ret)
+                        break;
+                ret = !(fs_devices->num_devices == fs_devices->total_devices);
+                break;
         }
 
         kfree(vol);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 957bf393ab46..39a0d04759f8 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -429,6 +429,7 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
         mutex_init(&fs_devices->device_list_mutex);
         fs_devices->latest_devid = orig->latest_devid;
         fs_devices->latest_trans = orig->latest_trans;
+        fs_devices->total_devices = orig->total_devices;
         memcpy(fs_devices->fsid, orig->fsid, sizeof(fs_devices->fsid));
 
         /* We have held the volume lock, it is safe to get the devices. */
@@ -739,6 +740,7 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
         int ret;
         u64 devid;
         u64 transid;
+        u64 total_devices;
 
         flags |= FMODE_EXCL;
         bdev = blkdev_get_by_path(path, flags, holder);
@@ -760,6 +762,7 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
         disk_super = (struct btrfs_super_block *)bh->b_data;
         devid = btrfs_stack_device_id(&disk_super->dev_item);
         transid = btrfs_super_generation(disk_super);
+        total_devices = btrfs_super_num_devices(disk_super);
         if (disk_super->label[0])
                 printk(KERN_INFO "device label %s ", disk_super->label);
         else
@@ -767,7 +770,8 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
         printk(KERN_CONT "devid %llu transid %llu %s\n",
                (unsigned long long)devid, (unsigned long long)transid, path);
         ret = device_list_add(path, disk_super, devid, fs_devices_ret);
-
+        if (!ret && fs_devices_ret)
+                (*fs_devices_ret)->total_devices = total_devices;
         brelse(bh);
 error_close:
         mutex_unlock(&uuid_mutex);
@@ -1433,6 +1437,7 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
         list_del_rcu(&device->dev_list);
 
         device->fs_devices->num_devices--;
+        device->fs_devices->total_devices--;
 
         if (device->missing)
                 root->fs_info->fs_devices->missing_devices--;
@@ -1550,6 +1555,7 @@ static int btrfs_prepare_sprout(struct btrfs_root *root)
         fs_devices->seeding = 0;
         fs_devices->num_devices = 0;
         fs_devices->open_devices = 0;
+        fs_devices->total_devices = 0;
         fs_devices->seed = seed_devices;
 
         generate_random_uuid(fs_devices->fsid);
@@ -1749,6 +1755,7 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
         root->fs_info->fs_devices->num_devices++;
         root->fs_info->fs_devices->open_devices++;
         root->fs_info->fs_devices->rw_devices++;
+        root->fs_info->fs_devices->total_devices++;
         if (device->can_discard)
                 root->fs_info->fs_devices->num_can_discard++;
         root->fs_info->fs_devices->total_rw_bytes += device->total_bytes;
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index e404414a95a9..5479325987b3 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -126,6 +126,7 @@ struct btrfs_fs_devices {
         u64 missing_devices;
         u64 total_rw_bytes;
         u64 num_can_discard;
+        u64 total_devices;
         struct block_device *latest_bdev;
 
         /* all of the devices in the FS, protected by a mutex