Re: [PATCH 2/2] btrfs: introduce feature to ignore a btrfs device

[Anand Jain]

On 11/16/2017 10:03 PM, Nikolay Borisov wrote:

On 13.11.2017 07:44, Anand Jain wrote:

Support for a new command is being added here:
  btrfs dev ignore <dev>
Which shall undo the effects of the command
  btrfs dev scan <dev>

This cli/ioctl is needed as there is no way to continue to mount in
degraded mode if the device is already scanned, which is required to
recover from the split brain raid conditions.

This patch proposes to use ioctl #5 as it was empty.
        IOW(BTRFS_IOCTL_MAGIC, 5, ..)
If #5 is reserved for some other purpose, I think I should change this.

Signed-off-by: Anand Jain <anand.j...@oracle.com>
---
  fs/btrfs/super.c           |  4 +++
  fs/btrfs/volumes.c         | 70 ++++++++++++++++++++++++++++++++++++++++++++++
  fs/btrfs/volumes.h         |  2 ++
  include/uapi/linux/btrfs.h |  2 ++
  4 files changed, 78 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index fa7bad8b22da..64f4beb1526d 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2183,6 +2183,10 @@ 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_IGNORE_DEV:
+               ret = btrfs_ignore_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);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8ead85dba6f5..1a06a17e111e 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1181,6 +1181,76 @@ int btrfs_read_disk_super(struct block_device *bdev, u64 
bytenr,
        return 0;
  }

+static int device_list_remove(struct btrfs_super_block *disk_super, u64 devid)

+{
+       int ret = 0;
+       struct btrfs_fs_devices *fs_devices;
+       struct btrfs_device *device;
+
+       fs_devices = find_fsid(disk_super->fsid);
+       if (!fs_devices)
+               return -ENOENT;
+
+       if (fs_devices->opened)
+               return -EPERM;

Isn't -EBUSY more appropriate?

 Right added.

Thanks, Anand

+
+       mutex_lock(&uuid_mutex);
+       mutex_lock(&fs_devices->device_list_mutex);
+       device = find_device(fs_devices, devid, disk_super->dev_item.uuid);
+       if (!device) {
+               ret = -ENOENT;
+               goto error;
+       }
+
+       delete_device_from_list(device);
+
+error:
+       mutex_unlock(&fs_devices->device_list_mutex);
+       mutex_unlock(&uuid_mutex);
+
+       return ret;
+}
+
+int btrfs_ignore_one_device(const char *path, fmode_t flags, void *holder,
+                         struct btrfs_fs_devices **fs_devices_ret)
+{
+       struct btrfs_super_block *disk_super;
+       struct block_device *bdev;
+       struct page *page;
+       int ret = -EINVAL;
+       u64 devid;
+       u64 bytenr;
+
+       bytenr = btrfs_sb_offset(0);
+       flags |= FMODE_EXCL;
+
+       bdev = blkdev_get_by_path(path, flags, holder);
+       if (IS_ERR(bdev)) {
+               ret = PTR_ERR(bdev);
+               goto error;
+       }
+
+       if (btrfs_read_disk_super(bdev, bytenr, &page, &disk_super))
+               goto error_bdev_put;
+
+       devid = btrfs_stack_device_id(&disk_super->dev_item);
+
+       ret = device_list_remove(disk_super, devid);
+       if (ret)
+       pr_err("BTRFS: %pU: device %s uuid %pU devid %llu failed to unscan: %d",
+               disk_super->fsid, path, disk_super->dev_item.uuid, devid, ret);
+       else
+       pr_info("BTRFS: %pU: device %s uuid %pU devid %llu ran undo scan",
+               disk_super->fsid, path, disk_super->dev_item.uuid, devid);
+
+       btrfs_release_disk_super(page);
+
+error_bdev_put:
+       blkdev_put(bdev, flags);
+error:
+       return ret;
+}
+
  /*
   * Look for a btrfs signature on a device. This may be called out of the 
mount path
   * and we are not allowed to call set_blocksize during the scan. The 
superblock
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 6108fdfec67f..340e40acdab5 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -421,6 +421,8 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
                       fmode_t flags, void *holder);
  int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
                          struct btrfs_fs_devices **fs_devices_ret);
+int btrfs_ignore_one_device(const char *path, fmode_t flags, void *holder,
+                         struct btrfs_fs_devices **fs_devices_ret);
  int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);
  void btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices, int step);
  void btrfs_assign_next_active_device(struct btrfs_fs_info *fs_info,
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 378230c163d5..928485c31aa4 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -739,6 +739,8 @@ enum btrfs_err_code {
                                   struct btrfs_ioctl_vol_args)
  #define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \
                                   struct btrfs_ioctl_vol_args)
+#define BTRFS_IOC_IGNORE_DEV _IOW(BTRFS_IOCTL_MAGIC, 5, \
+                                  struct btrfs_ioctl_vol_args)
  /* trans start and trans end are dangerous, and only for
   * use by applications that know how to avoid the
   * resulting deadlocks

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