[RESEND,v12] btrfs: introduce feature to forget a btrfs device

Commit Message

Anand Jain Nov. 30, 2018, 8:52 a.m. UTC

Support for a new command 'btrfs dev forget [dev]' is proposed here
to undo the effects of 'btrfs dev scan [dev]'. For this purpose
this patch proposes to use ioctl #5 as it was empty.
	IOW(BTRFS_IOCTL_MAGIC, 5, ..)
This patch adds new ioctl BTRFS_IOC_FORGET_DEV which can be sent from
the /dev/btrfs-control to forget one or all devices, (devices which are
not mounted) from the btrfs kernel.

The argument it takes is struct btrfs_ioctl_vol_args, and ::name can be
set to specify the device path. And all unmounted devices can be removed
from the kernel if no device path is provided.

Again, the devices are removed only if the relevant fsid aren't mounted.

This new cli can provide..
 . Release of unwanted btrfs_fs_devices and btrfs_devices memory if the
   device is not going to be mounted.
 . Ability to mount the device in degraded mode when one of the other
   device is corrupted like in split brain raid1.
 . Running test cases which requires btrfs.ko-reload if the rootfs
   is btrfs.

Signed-off-by: Anand Jain <[e-mail]>
Reviewed-by: Nikolay Borisov <[e-mail]>
---
v11->v12: fix coding style add spacing before after ":".
v1->v11: Pls ref to the cover-letter. (sorry about that).

 fs/btrfs/super.c           | 3 +++
 fs/btrfs/volumes.c         | 9 +++++++++
 fs/btrfs/volumes.h         | 1 +
 include/uapi/linux/btrfs.h | 2 ++
 4 files changed, 15 insertions(+)

Patch

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d3c6bbc0aa3a..eba2966913ae 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2247,6 +2247,9 @@  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,
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8e36cbb355df..48415a9edd46 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1397,6 +1397,15 @@  static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
 	return 0;
 }
 
+int btrfs_forget_devices(const char *path)
+{
+	mutex_lock(&uuid_mutex);
+	btrfs_free_stale_devices(strlen(path) ? path : NULL, NULL);
+	mutex_unlock(&uuid_mutex);
+
+	return 0;
+}
+
 /*
  * 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 1d936ce282c3..a4a89d5050f5 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -414,6 +414,7 @@  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,
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index e0763bc4158e..c195896d478f 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -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