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

[Anand Jain <anand.jain@oracle.com>]

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.jain@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
>>