Commit 228a73ab authored by Anand Jain's avatar Anand Jain Committed by David Sterba
Browse files

btrfs: introduce new ioctl to unregister a btrfs device 



Support for a new command that can be used eg. as a command

  $ btrfs device scan --forget [dev]'
(the final name may change though)

to undo the effects of 'btrfs device scan [dev]'. For this purpose
this patch proposes to use ioctl #5 as it was empty and is next to the
SCAN ioctl.

The new ioctl BTRFS_IOC_FORGET_DEV works only on the control device
(/dev/btrfs-control) to unregister one or all devices, devices that are
not mounted.

The argument is struct btrfs_ioctl_vol_args, ::name specifies the device
path. To unregister all device, the path is an empty string.

Again, the devices are removed only if they aren't part of a mounte
filesystem.

This new ioctl provides:

- release of unwanted btrfs_fs_devices and btrfs_devices structures
  from memory if the device is not going to be mounted

- ability to mount filesystem in degraded mode, when one devices is
  corrupted like in split brain raid1

- running test cases which would require reloading the kernel module
  but this is not possible eg. due to mounted filesystem or built-in

Signed-off-by: default avatarAnand Jain <anand.jain@oracle.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 034f784d

fs/btrfs/super.c

+3 −0
Original line number Diff line number Diff line
@@ -2190,6 +2190,9 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd, 
		ret = PTR_ERR_OR_ZERO(device);

		mutex_unlock(&uuid_mutex);

		break;

	case BTRFS_IOC_FORGET_DEV:

		ret = btrfs_forget_devices(vol->name);

		break;

	case BTRFS_IOC_DEVICES_READY:

		mutex_lock(&uuid_mutex);

		device = btrfs_scan_one_device(vol->name, FMODE_READ,

fs/btrfs/volumes.c

+11 −0
Original line number Diff line number Diff line
@@ -1446,6 +1446,17 @@ static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr, 
	return 0;

}



int btrfs_forget_devices(const char *path)

{

	int ret;



	mutex_lock(&uuid_mutex);

	ret = btrfs_free_stale_devices(strlen(path) ? path : NULL, NULL);

	mutex_unlock(&uuid_mutex);



	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

fs/btrfs/volumes.h

+1 −0
Original line number Diff line number Diff line
@@ -416,6 +416,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices, 
		       fmode_t flags, void *holder);

struct btrfs_device *btrfs_scan_one_device(const char *path,

					   fmode_t flags, void *holder);

int btrfs_forget_devices(const char *path);

int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);

void btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, int step);

void btrfs_assign_next_active_device(struct btrfs_device *device,

include/uapi/linux/btrfs.h

+2 −0
Original line number Diff line number Diff line
@@ -837,6 +837,8 @@ 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_FORGET_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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