[Ocfs2-devel] [PATCH] ocfs2: Fill-in the unused portion of the block with zeros by dio_zero_block()

[jiangyiwen]

On 2015/9/9 18:42, Zhen Ren wrote:
> Hi Joseph and Yiwen,
> 
> Sorry for that misoperation. 
> 
> This time, I did the same cmds using "hexdump" on ocfs2 and btrfs.
> The testing results look the same:
> ==
> laptop:/mnt/shared # dd if=/dev/zero of=hello bs=512 count=1 oflag=direct                                    ===> on ocfs2
> 1+0 records in
> 1+0 records out
> 512 bytes (512 B) copied, 0.000834866 s, 613 kB/s
> laptop:/mnt/shared # hexdump hello -C
> 00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> *
> 00000200
> laptop:/mnt/shared # truncate hello -s 2097152
> laptop:/mnt/shared # truncate hello -s 2097152
> laptop:/mnt/shared # hexdump hello -C
> 00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> *
> 00200000
> 
> laptop:~ # dd if=/dev/zero of=hello bs=512 count=1 oflag=direct                                                                         ===> on btrfs
> 1+0 records in
> 1+0 records out
> 512 bytes (512 B) copied, 0.000201759 s, 2.5 MB/s
> laptop:~ # hexdump hello -C
> 00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> *
> 00000200
> laptop:~ # truncate hello -s 2097152
> laptop:~ # hexdump hello -C
> 00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> *
> 00200000
> ==
> 
> BTW, Yiwen, I'm confused by your comment and commit message.
> 1. >> file 'hello' should be all zero. But 512~4096 is some random data. 
>  2. it means in file area 512~4096 is zero not random data.
> 
> Anyway, I didn't look into this case, but just try to understand it. 
> So, if there's any problem, let it go ;-)
sorry, my description is wrong, 512~4096 is zero.

Thanks,
Yiwen Jiang
> 
> Thanks.
> --
> Eric Ren
> 
>>>> Joseph Qi <joseph.qi at huawei.com> 09/09/15 6:04 PM >>>
> Hi Zhen,
> 
> On 2015/9/9 13:16, Zhen Ren wrote:
>> Hi Yiwen,
>>
>> I try to reproduce this case, but it didn't act like you describe.
>> What I did: 
>> ===
>> laptop:/mnt/shared # mount | grep ocfs2
>> ocfs2_dlmfs on /dlm type ocfs2_dlmfs (rw,relatime)
>> /dev/sda3 on /mnt/shared type ocfs2 (rw,relatime,_netdev,heartbeat=local,nointr,data=ordered,errors=remount-ro,atime_quantum=60,coherency=full,user_xattr,acl)
>> laptop:/mnt/shared # dd if=/dev/zero of=/mnt/shared/hello bs=512 count=1 oflag=direct
>> 1+0 records in
>> 1+0 records out
>> 512 bytes (512 B) copied, 0.000684382 s, 748 kB/s
>> laptop:/mnt/shared # truncate hello -s 2097152
>> laptop:/mnt/shared # cat hello                            ======> nothing
> I don't think 'cat' works here.
> Could you please use hexdump?
> 
>> laptop:/mnt/shared # uname -r
>> 3.16.7-21-desktop
>> ===
>>
>> Did I do something wrong? If I misunderstand, please correct me.
>> Thanks.
>>
>>  >>>
>>> A simplified test case is (this case from Ryan): 
>>> 1) dd if=/dev/zero of=/mnt/hello bs=512 count=1 oflag=direct; 
>>> 2) truncate /mnt/hello -s 2097152 
>>> file 'hello' is not exist before test. After this command, 
>>> file 'hello' should be all zero. But 512~4096 is some random data. 
>>>  
>>> Setting bh state to new when get a new block, if so, 
>>> direct_io_worker()->dio_zero_block() will fill-in the unused portion 
>>> of the block with zero. 
>>>  
>>> Signed-off-by: Yiwen Jiang <jiangyiwen at huawei.com> 
>>> --- 
>>>  fs/ocfs2/aops.c | 1 + 
>>>  1 file changed, 1 insertion(+) 
>>>  
>>> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c 
>>> index 1a35c61..bd106b9 100644 
>>> --- a/fs/ocfs2/aops.c 
>>> +++ b/fs/ocfs2/aops.c 
>>> @@ -581,6 +581,7 @@ static int ocfs2_direct_IO_get_blocks(struct inode  
>>> *inode, sector_t iblock, 
>>>  			ret = -EIO; 
>>>  			goto bail; 
>>>  		} 
>>> +		set_buffer_new(bh_result); 
>>>  	} 
>>>  
>>>  	/* 
>>  
>>
>>
>>
>> --
>> Eric, Ren
>>
>>
>>
>>
>> _______________________________________________
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>> Ocfs2-devel at oss.oracle.com
>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
>>
>>
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