btrfs: add device delete cancel

Accept device name "cancel" as a request to cancel running device
deletion operation. The string is literal, in case there's a real device
named "cancel", pass it as full absolute path or as "./cancel"

This works for v1 and v2 ioctls when the device is specified by name.
Moving chunks from the device uses relocation, use the conditional
exclusive operation start and cancellation helpers

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 24 insertions, 19 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 157ead83d65c..2bdaf2018197 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3206,6 +3206,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	struct btrfs_ioctl_vol_args_v2 *vol_args;
 	int ret;
+	bool cancel = false;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -3224,18 +3225,22 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
 		ret = -EOPNOTSUPP;
 		goto out;
 	}
+	vol_args->name[BTRFS_SUBVOL_NAME_MAX] = '\0';
+	if (!(vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID) &&
+	    strcmp("cancel", vol_args->name) == 0)
+		cancel = true;
 
-	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_DEV_REMOVE)) {
-		ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
+	ret = exclop_start_or_cancel_reloc(fs_info, BTRFS_EXCLOP_DEV_REMOVE,
+					   cancel);
+	if (ret)
 		goto out;
-	}
+	/* Exclusive operation is now claimed */
 
-	if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID) {
+	if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID)
 		ret = btrfs_rm_device(fs_info, NULL, vol_args->devid);
-	} else {
-		vol_args->name[BTRFS_SUBVOL_NAME_MAX] = '\0';
+	else
 		ret = btrfs_rm_device(fs_info, vol_args->name, 0);
-	}
+
 	btrfs_exclop_finish(fs_info);
 
 	if (!ret) {
@@ -3259,6 +3264,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	struct btrfs_ioctl_vol_args *vol_args;
 	int ret;
+	bool cancel;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -3267,25 +3273,24 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
 	if (ret)
 		return ret;
 
-	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_DEV_REMOVE)) {
-		ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
-		goto out_drop_write;
-	}
-
 	vol_args = memdup_user(arg, sizeof(*vol_args));
 	if (IS_ERR(vol_args)) {
 		ret = PTR_ERR(vol_args);
-		goto out;
+		goto out_drop_write;
 	}
-
 	vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
-	ret = btrfs_rm_device(fs_info, vol_args->name, 0);
+	cancel = (strcmp("cancel", vol_args->name) == 0);
+
+	ret = exclop_start_or_cancel_reloc(fs_info, BTRFS_EXCLOP_DEV_REMOVE,
+					   cancel);
+	if (ret == 0) {
+		ret = btrfs_rm_device(fs_info, vol_args->name, 0);
+		if (!ret)
+			btrfs_info(fs_info, "disk deleted %s", vol_args->name);
+		btrfs_exclop_finish(fs_info);
+	}
 
-	if (!ret)
-		btrfs_info(fs_info, "disk deleted %s", vol_args->name);
 	kfree(vol_args);
-out:
-	btrfs_exclop_finish(fs_info);
 out_drop_write:
 	mnt_drop_write_file(file);