linux-ext4 - Re: Copying Data Blocks

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Date:	Tue, 6 Jan 2009 22:58:13 +0530
From:	"Manish Katiyar" <mkatiyar@...il.com>
To:	"Rohit Sharma" <imreckless@...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 10:55 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 ?

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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