linux-ext4 - Re: Copying Data Blocks

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Date:	Tue, 6 Jan 2009 23:06:16 +0530
From:	"Rohit Sharma" <imreckless@...il.com>
To:	"Manish Katiyar" <mkatiyar@...il.com>
Cc:	"rishi agrawal" <postrishi@...il.com>,
	ext4 <linux-ext4@...r.kernel.org>,
	Kernelnewbies <kernelnewbies@...linux.org>
Subject: Re: Copying Data Blocks

On Tue, Jan 6, 2009 at 10:58 PM, Manish Katiyar <mkatiyar@...il.com> wrote:
> On Tue, Jan 6, 2009 at 10:55 PM, Rohit Sharma <imreckless@...il.com> wrote:
>> We can find out no. of block currently being used by the donor inode,
>> The data we read from donor inode has to be in some buffer or page,
>
> Since we know the blocknumber of donor inode, it should be possible to
> do a raw read and get the memory address of the data page using
> sb_bread() and then accessing bh->b_data . Isn't it ?

Yes that's the way we can read blocks but the major issue here
is copying this content to newly allocated block.
>
> Thanks -
> Manish
>
>> is there a way we can associate this buffer with the reciever inode
>> or write the contents of the buffer to the new inode.
>>
>>
>> On Tue, Jan 6, 2009 at 10:46 PM, Rohit Sharma <imreckless@...il.com> wrote:
>>> On Tue, Jan 6, 2009 at 10:43 PM, Manish Katiyar <mkatiyar@...il.com> wrote:
>>>> On Tue, Jan 6, 2009 at 10:15 PM, Rohit Sharma <imreckless@...il.com> wrote:
>>>>> On Tue, Jan 6, 2009 at 7:42 PM, rishi agrawal <postrishi@...il.com> wrote:
>>>>>> yes i suppose the donor inode is known
>>>>>> moreover the receiver inode's number is also known
>>>>>>
>>>>>> On Tue, Jan 6, 2009 at 6:54 PM, Manish Katiyar <mkatiyar@...il.com> wrote:
>>>>>>>
>>>>>>> On Tue, Jan 6, 2009 at 4:06 PM, Rohit Sharma <imreckless@...il.com> wrote:
>>>>>>> > I want to read data blocks from one inode
>>>>>>> > and copy it to other inode.
>>>>>>> >
>>>>>>> > I mean to copy data from data blocks associated with one inode
>>>>>>> > to the data blocks associated with other inode.
>>>>>>>
>>>>>>> Copying 4K chunk of data itself is a costly operation. and depending
>>>>>
>>>>> Yes its a costly operation, but if this can be done then
>>>>> we can definitely copy n blocks at a time.
>>>>>
>>>>>>> on the size of your donor inode this can be huge . Why do you want to
>>>>>>> do that ? Do you know the inode of the donor inode ?
>>>>>
>>>>> For physically relocating a file from one disk to other.
>>>>>
>>>>> Yes Manish, i know the donor inode and i will create the reciever inode.
>>>>
>>>> I am guessing .......will something like this work ?
>>>>
>>>> ino_t donor_inode_num;
>>>> struct inode *donor_inode = FS_iget(sb , donor_inode_num);
>>>> struct FS_inode_info * fsi = FSI(donor_inode) ;   // Do the regular
>>>> container_of stuff here
>>>>
>>>> for ( i = 0; i < (donor_inode->i_size + sb->s_blocksize -
>>>> 1)/sb->s_blocksize ; i ++ ) {
>>>>    // Do a memmove or memcpy here from fsi->i_data[i]
>>>> }
>>>>
>>>> I am not sure though how will you prevent the donor inode from being
>>>> changed/resized during this period.
>>>
>>> I am thinking of remounting ext2 in readonly mode, or i'll change the
>>> mount flags to readonly. But i m not sure if internally i can copy the
>>> data from one block to other.
>>>
>>>>
>>>> Thanks -
>>>> Manish
>>>>
>>>>
>>>>>
>>>>> Can we do that in kernel space.?
>>>>>>>
>>>>>>> thanks -
>>>>>>> Manish
>>>>>>> >
>>>>>>> > Is that possible in kernel space.?
>>>>>>> > --
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>>>>>>> >
>>>>>>> --
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>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Regards,
>>>>>> Rishi B. Agrawal
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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