On 2019/11/1 下午6:52, David Sterba wrote:
> On Sat, Oct 26, 2019 at 06:11:27PM +0800, Qu Wenruo wrote:
>> + /*
>> + * Log tree only exists in the primary super block, so SBREAD_DEFAULT
>> + * is enough.
>
> For read it should be enough to read the default one, but do you mean
> that 1st and 2nd copy don't have the log_root values set? They're
> written from the same buffer so I'd expect the contents to be the same.
Log tree update only happens for primary sb.
The kernel code has this:
btrfs_sync_log()
|- ret = write_all_supers(fs_info, 1)
|- write_dev_supers(max_mirrors); # max_mirrors == 1
|- for (i = 0; i < max_mirrors; i++)
>
>> + ret = btrfs_read_dev_super(fd, sb, BTRFS_SUPER_INFO_OFFSET,
>> + SBREAD_DEFAULT);
>> + if (ret < 0) {
>> + errno = -ret;
>> + error("failed to read super block on '%s': %m", devname);
>> + goto close_fd;
>> }
>>
>> - sb = root->fs_info->super_copy;
>> printf("Clearing log on %s, previous log_root %llu, level %u\n",
>> devname,
>> (unsigned long long)btrfs_super_log_root(sb),
>> (unsigned)btrfs_super_log_root_level(sb));
>> - trans = btrfs_start_transaction(root, 1);
>> - BUG_ON(IS_ERR(trans));
>> btrfs_set_super_log_root(sb, 0);
>> btrfs_set_super_log_root_level(sb, 0);
>> - btrfs_commit_transaction(trans, root);
>> - close_ctree(root);
>> + btrfs_csum_data(btrfs_super_csum_type(sb), (u8 *)sb + BTRFS_CSUM_SIZE,
>> + result, BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
>> + memcpy(&sb->csum[0], result, BTRFS_CSUM_SIZE);
>> + ret = pwrite64(fd, sb, BTRFS_SUPER_INFO_SIZE, BTRFS_SUPER_INFO_OFFSET);
>
> So this only writes on the one device that's passed to the command.
> Previously it would update superblocks on all devices.
Oh, you got me.
That's indeed the case. I guess we need to do the same skip_bg behavior
just like kernel to handle multiple devices.
Thanks,
Qu
