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

[Zhen Ren]

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 ;-)

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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