linux-kernel - Re: [PATCH 1/1] btrfs: btrfs_calc_avail_data_space cope with no read/write devices V2

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Date:	Tue, 29 Nov 2011 09:55:10 +0800
From:	Miao Xie <miaox@...fujitsu.com>
To:	Jonathan Nieder <jrnieder@...il.com>
CC:	Chris Mason <chris.mason@...cle.com>,
	Andy Whitcroft <apw@...onical.com>,
	Josef Bacik <josef@...hat.com>,
	Ivan Vilata i Balaguer <ivan@...idor.net>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] btrfs: btrfs_calc_avail_data_space cope with no read/write
 devices V2

On mon, 28 Nov 2011 06:11:06 -0600, Jonathan Nieder wrote:
> Hi,
> 
> Andy Whitcroft wrote:
> 
>> When we mount a btrfs filesystem from read-only media there will be no
>> read/write devices; for example mounting an SD card with its lock enabled.
>> This triggers an immediate BUG during mount:
>>
>>   kernel BUG at .../fs/btrfs/super.c:984!
> [...]
>> BugLink: http://bugs.launchpad.net/bugs/816770
>> Signed-off-by: Andy Whitcroft <apw@...onical.com>
>> ---
> 
> Fixes http://bugs.debian.org/649847
> Tested-by: Ivan Vilata i Balaguer <ivan@...idor.net>
> 
> This patch fixes a regression introduced by 6d07bcec969a ("btrfs: fix
> wrong free space information of btrfs"), which hit mainline in
> v2.6.38-rc1.  Josef Bacik acked the patch, but I can't seem to find it
> in linux-next, linux-btrfs, or Josef's btrfs-work tree.  Maybe it was
> just forgotten.
> 
> What can I do to help this patch get unstuck?

I think We should make this behaviour similar to the traditional file systems,
such as ext3/4. That is the available space should show the size of all the free space
which we may used to store the file data, even we mount it on the read-only mode.
This patch didn't fix the problem completely.

Thanks
Miao

>>  fs/btrfs/super.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>> index 15634d4..ae4367a 100644
>> --- a/fs/btrfs/super.c
>> +++ b/fs/btrfs/super.c
>> @@ -980,7 +980,7 @@ static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes)
>>  	int i = 0, nr_devices;
>>  	int ret;
>>  
>> -	nr_devices = fs_info->fs_devices->rw_devices;
>> +	nr_devices = fs_info->fs_devices->open_devices;
>>  	BUG_ON(!nr_devices);
>>  
>>  	devices_info = kmalloc(sizeof(*devices_info) * nr_devices,
>> -- 
>> 1.7.4.1
>>
> --
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