Re: [PATCH] Btrfs: add label to snapshot and subvol

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

Hi Jan,

  Thanks for the review. Just posted the v2 patch for the
  btrfs kernel patch.
  Which, used the btrfs_root_item reserved space and
  used join_transaction

-Anand

On 05/11/12 15:39, Jan Schmidt wrote:
> Hi Anand,
>
> Some comments on your kernel patch from a quick jump through:
>
> On 01.11.2012 11:46, Anand jain wrote:
>> From: Anand Jain <anand.jain@oracle.com>
>>
>> This modifies the struct btrfs_root_item to hold the label,
>> and make it v3 of this structure.
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>>   fs/btrfs/ctree.h       |   14 ++++++++++++++
>>   fs/btrfs/ioctl.c       |   32 ++++++++++++++++++++++++++++++++
>>   fs/btrfs/ioctl.h       |    2 ++
>>   fs/btrfs/root-tree.c   |   44 +++++++++++++++++++++++---------------------
>>   fs/btrfs/transaction.c |    1 +
>>   5 files changed, 72 insertions(+), 21 deletions(-)
>>
>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>> index 994d255..b280256 100644
>> --- a/fs/btrfs/ctree.h
>> +++ b/fs/btrfs/ctree.h
>> @@ -759,6 +759,10 @@ struct btrfs_root_item {
>>   	struct btrfs_timespec otime;
>>   	struct btrfs_timespec stime;
>>   	struct btrfs_timespec rtime;
>> +
>> +	__le64 generation_v3;
>
> What is that supposed to be?
>
>> +	char label[BTRFS_LABEL_SIZE]; /* Add label to subvol */
>> +	
>>   	__le64 reserved[8]; /* for future */
>>   } __attribute__ ((__packed__));
>
> You can't do that. There's a reason why we've got reserved bytes for
> future use. Never change the struct's size.
>
>> @@ -2428,6 +2432,8 @@ BTRFS_SETGET_STACK_FUNCS(root_last_snapshot, struct btrfs_root_item,
>>   			 last_snapshot, 64);
>>   BTRFS_SETGET_STACK_FUNCS(root_generation_v2, struct btrfs_root_item,
>>   			 generation_v2, 64);
>> +BTRFS_SETGET_STACK_FUNCS(root_generation_v3, struct btrfs_root_item,
>> +			 generation_v3, 64);
>>   BTRFS_SETGET_STACK_FUNCS(root_ctransid, struct btrfs_root_item,
>>   			 ctransid, 64);
>>   BTRFS_SETGET_STACK_FUNCS(root_otransid, struct btrfs_root_item,
>> @@ -2441,6 +2447,14 @@ static inline bool btrfs_root_readonly(struct btrfs_root *root)
>>   {
>>   	return (root->root_item.flags & cpu_to_le64(BTRFS_ROOT_SUBVOL_RDONLY)) != 0;
>>   }
>> +static inline char * btrfs_root_label(struct btrfs_root *root)
>> +{
>> +	return (root->root_item.label);
>> +}
>> +static inline void btrfs_root_set_label(struct btrfs_root *root, char *val)
>> +{
>> +	memcpy(root->root_item.label,val,BTRFS_LABEL_SIZE);
>> +}
>>
>>   /* struct btrfs_root_backup */
>>   BTRFS_SETGET_STACK_FUNCS(backup_tree_root, struct btrfs_root_backup,
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index e58bd9d..cce0128 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -3725,6 +3725,34 @@ static int btrfs_ioctl_set_label(struct btrfs_root *root, void __user *arg)
>>   	return 0;
>>   }
>>
>> +static int btrfs_ioctl_subvol_getlabel(struct btrfs_root *root,
>> +						void __user *arg)
>> +{
>> +	char *label;
>> +
>> +	label = btrfs_root_label(root);
>> +	if (copy_to_user(arg, label, BTRFS_LABEL_SIZE))
>> +		return -EFAULT;
>> +	return 0;
>> +}
>> +
>> +static int btrfs_ioctl_subvol_setlabel(struct btrfs_root *root,
>> +						void __user *arg)
>> +{
>> +	char label[BTRFS_LABEL_SIZE];
>> +	struct btrfs_trans_handle *trans;
>> +
>> +	if (copy_from_user(label, arg, BTRFS_LABEL_SIZE))
>> +		return -EFAULT;
>> +	trans = btrfs_start_transaction(root, 1);
>> +	if (IS_ERR(trans))
>> +		return PTR_ERR(trans);
>> +	btrfs_root_set_label(root, label);
>> +	btrfs_commit_transaction(trans, root);
>
> Why use start/commit instead of join/end here?
>
>> +	return 0;
>> +}
>> +
>>   long btrfs_ioctl(struct file *file, unsigned int
>>   		cmd, unsigned long arg)
>>   {
>> @@ -3827,6 +3855,10 @@ long btrfs_ioctl(struct file *file, unsigned int
>>   		return btrfs_ioctl_get_label(root, argp);
>>   	case BTRFS_IOC_SET_LABEL:
>>   		return btrfs_ioctl_set_label(root, argp);
>> +	case BTRFS_IOC_SUBVOL_GETLABEL:
>> +		return btrfs_ioctl_subvol_getlabel(root, argp);
>> +	case BTRFS_IOC_SUBVOL_SETLABEL:
>> +		return btrfs_ioctl_subvol_setlabel(root, argp);
>>   	}
>>
>>   	return -ENOTTY;
>> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
>> index 0c60fcb..1009a0c 100644
>> --- a/fs/btrfs/ioctl.h
>> +++ b/fs/btrfs/ioctl.h
>> @@ -455,4 +455,6 @@ struct btrfs_ioctl_send_args {
>>   				      struct btrfs_ioctl_get_dev_stats)
>>   #define BTRFS_IOC_GET_LABEL _IOR(BTRFS_IOCTL_MAGIC, 53, __u64)
>>   #define BTRFS_IOC_SET_LABEL _IOW(BTRFS_IOCTL_MAGIC, 54, __u64)
>> +#define BTRFS_IOC_SUBVOL_GETLABEL _IOWR(BTRFS_IOCTL_MAGIC, 55, __u64)
>> +#define BTRFS_IOC_SUBVOL_SETLABEL _IOW(BTRFS_IOCTL_MAGIC, 56, __u64)
>>   #endif
>> diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
>> index eb923d0..2a9ae5f 100644
>> --- a/fs/btrfs/root-tree.c
>> +++ b/fs/btrfs/root-tree.c
>> @@ -35,32 +35,34 @@ void btrfs_read_root_item(struct btrfs_root *root,
>>   {
>>   	uuid_le uuid;
>>   	int len;
>> -	int need_reset = 0;
>>
>>   	len = btrfs_item_size_nr(eb, slot);
>>   	read_extent_buffer(eb, item, btrfs_item_ptr_offset(eb, slot),
>>   			min_t(int, len, (int)sizeof(*item)));
>> -	if (len < sizeof(*item))
>> -		need_reset = 1;
>> -	if (!need_reset && btrfs_root_generation(item)
>> -		!= btrfs_root_generation_v2(item)) {
>> -		if (btrfs_root_generation_v2(item) != 0) {
>> -			printk(KERN_WARNING "btrfs: mismatching "
>> -					"generation and generation_v2 "
>> -					"found in root item. This root "
>> -					"was probably mounted with an "
>> -					"older kernel. Resetting all "
>> -					"new fields.\n");
>
> Please argue why removing this without replacement should be a good idea.
>
>> -		}
>> -		need_reset = 1;
>> -	}
>> -	if (need_reset) {
>> -		memset(&item->generation_v2, 0,
>> -			sizeof(*item) - offsetof(struct btrfs_root_item,
>> -					generation_v2));
>>
>> -		uuid_le_gen(&uuid);
>> -		memcpy(item->uuid, uuid.b, BTRFS_UUID_SIZE);
>> +	/* when len is gt sizeof(*item) that means its downgrade and
>> +	   the new members won't be touched anyways
>> +	   if len is lt sizeof(*item) its upgrade, we need to take
>> +	   care to set/reset newer members.
>> +	*/
>> +	if (len < sizeof(*item)) {
>> +		/* there is an upgrade need to set/reset the new members
>> +		   assume v1 v2 v3 it can be upgrade from
>> +			v1 to v2 (set/reset only new members of v2)
>> +			v2 to v3 (set/reset only new members of v3)
>> +			v1 to v3 (set/reset new to v1)
>> +		*/
>> +		if (btrfs_root_generation(item) != btrfs_root_generation_v2(item)) {
>> +			//memset(&item->generation_v2, 0,
>> +				//sizeof(*item) - offsetof(struct btrfs_root_item, generation_v2));
>> +			memset(&item->generation_v2, 0, sizeof(*item) - len);
>> +			uuid_le_gen(&uuid);
>> +			memcpy(item->uuid, uuid.b, BTRFS_UUID_SIZE);
>> +		} else if (btrfs_root_generation_v2(item) != btrfs_root_generation_v3(item)) {
>> +			//memset(&item->generation_v3, 0,
>> +			//	sizeof(*item) - offsetof(struct btrfs_root_item, generation_v3));
>> +			memset(&item->generation_v3, 0, sizeof(*item) - len);
>> +		}
>>   	}
>>   }
>>
>> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
>> index 04bbfb1..45bff43 100644
>> --- a/fs/btrfs/transaction.c
>> +++ b/fs/btrfs/transaction.c
>> @@ -1116,6 +1116,7 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
>>   	btrfs_set_root_otransid(new_root_item, trans->transid);
>>   	memset(&new_root_item->stime, 0, sizeof(new_root_item->stime));
>>   	memset(&new_root_item->rtime, 0, sizeof(new_root_item->rtime));
>> +	memset(new_root_item->label, 0, BTRFS_LABEL_SIZE);
>>   	btrfs_set_root_stransid(new_root_item, 0);
>>   	btrfs_set_root_rtransid(new_root_item, 0);
>>
>>
>
> -Jan
> --
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