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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: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>
hifive-unleashed-5.1
Anand Jain 2019-01-04 13:31:54 +08:00 committed by David Sterba
parent 034f784d7c
commit 228a73abde
4 changed files with 17 additions and 0 deletions
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3
fs/btrfs/super.c
View File

@ -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,

11
fs/btrfs/volumes.c
View File

@ -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

1
fs/btrfs/volumes.h
View File

@ -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,

2
include/uapi/linux/btrfs.h
View File

@ -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