On Fri, 12 Apr 2013 09:02:34 +0200, Jan Schmidt wrote:
>>>> +static int btrfs_close_extend_iref(struct btrfs_fs_info *fs_info,
>>>> + unsigned long old_opts)
>>>
>>> The name irritated me, it's more like "unset" instead of "close", isn't it?
>>
>> Maybe "btrfs_set_no_extend_iref()" is better, the other developers might think
>> we will clear BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF.
>
> I think we should use the exact name of the mount option, so
> btrfs_set_noextiref is probably least ambiguous. Or even
> btrfs_set_mntflag_noextiref.
Much better than mine.
>>>
>>>> +{
>>>> + struct btrfs_trans_handle *trans;
>>>> + int ret;
>>>> +
>>>> + if (btrfs_raw_test_opt(old_opts, NOEXTIREF) ||
>>>> + !btrfs_raw_test_opt(fs_info->mount_opt, NOEXTIREF))
>>>> + return 0;
>>>> +
>>>> + trans = btrfs_attach_transaction(fs_info->tree_root);
>>>> + if (IS_ERR(trans)) {
>>>> + if (PTR_ERR(trans) != -ENOENT)
>>>> + return PTR_ERR(trans);
>>>> + } else {
>>>> + ret = btrfs_commit_transaction(trans, fs_info->tree_root);
>>>> + if (ret)
>>>> + return ret;
>>>> + }
>>>
>>> Huh? I don't see why we need to commit the transaction here. Can you please explain?
>>
>> We need avoid the case that we check incompat flag is set or not between the
>> extended iref insertion and incompat flag set.
>> Task1 Task2
>> start_transaction()
>> insert extended iref
>> set NOEXTIREF
>> check incompat flag
>> set incompat flag
>>
>> checking incompat flag after transaction commit can make sure our check happens
>> after the flag is set.
>
> Understood.
>
> However, in my understanding of transaction.c, btrfs_join_transaction,
> btrfs_attach_transaction and btrfs_commit_transaction are special and need
> justification. If you only need the transaction for synchronization purposes,
> which seems to be the case here, btrfs_start_transaction and
> btrfs_end_transaction are the right choice.
btrfs_end_transaction() does not wait for/force the other tasks to end their
transaction, so it is not right here.
Thanks
Miao
>
> Thanks,
> -Jan
>
>> Thanks
>> Miao
>>
>>>
>>> Thanks,
>>> -Jan
>>>
>>>> +
>>>> + if (btrfs_super_incompat_flags(fs_info->super_copy) &
>>>> + BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF) {
>>>> + printk(KERN_ERR "BTRFS: could not close extend iref.\n");
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> static inline void btrfs_remount_prepare(struct btrfs_fs_info *fs_info)
>>>> {
>>>> set_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state);
>>>> @@ -1259,6 +1293,11 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
>>>> }
>>>>
>>>> btrfs_remount_begin(fs_info, old_opts, *flags);
>>>> +
>>>> + ret = btrfs_close_extend_iref(fs_info, old_opts);
>>>> + if (ret)
>>>> + goto restore;
>>>> +
>>>> btrfs_resize_thread_pool(fs_info,
>>>> fs_info->thread_pool_size, old_thread_pool_size);
>>>>
>>>>
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>>
>
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