linux-ext4 - Re: Copying Data Blocks

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Date:	Tue, 6 Jan 2009 22:46:47 +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 10:43 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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