linux-ext4 - Re: Copying Data Blocks

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Date:	Mon, 12 Jan 2009 12:26:42 +0530
From:	"Sandeep K Sinha" <sandeepksinha@...il.com>
To:	"Rohit Sharma" <imreckless@...il.com>
Cc:	"Peter Teoh" <htmldeveloper@...il.com>,
	ext4 <linux-ext4@...r.kernel.org>,
	Kernelnewbies <kernelnewbies@...linux.org>
Subject: Re: Copying Data Blocks

Hi Rohit,

On Mon, Jan 12, 2009 at 11:48 AM, Rohit Sharma <imreckless@...il.com> wrote:
> Hi,
>
> I am having some issues in locking inode while copying data blocks.
> We are trying to keep file system live during this operation, so
> both read and write operations should work.
> In this case what type of lock on inode should be used, semaphore,
> mutex or spinlock?
>

Now here you need to do some homework first.
Each of the locks have its own meaning and particular uses cases.

The current inode struct has the following locks:
1. i_lock
2. i_alloc_sem
3. i_mutex
4. i_flock

 646        spinlock_t              i_lock; /* i_blocks, i_bytes,
maybe i_size */
 647        struct mutex            i_mutex;
 648        struct rw_semaphore     i_alloc_sem;
 649        const struct inode_operations   *i_op;
 650        const struct file_operations    *i_fop; /* former
->i_op->default_file_ops */
 651        struct super_block      *i_sb;
 652        struct file_lock        *i_flock;

Read the difference between spinlock, mutex, and semaphore.
You will be able to understand the semantics of each of these.

>
> On Sun, Jan 11, 2009 at 8:45 PM, Peter Teoh <htmldeveloper@...il.com> wrote:
>> Sorry.....some mistakes...a resent:
>>
>> Here are some tips on the blockdevice API:
>>
>> http://lkml.org/lkml/2006/1/24/287
>> http://linux.derkeiler.com/Mailing-Lists/Kernel/2006-01/msg09388.html
>>
>> as indicated, documentation is rather sparse in this area.
>>
>> not sure if anyone else have a summary list of blockdevice API and its
>> explanation?
>>
>> not wrt the following "cleanup patch", i am not sure how the API will change:
>>
>> http://lwn.net/Articles/304485/
>>
>> thanks.
>>
>> On Tue, Jan 6, 2009 at 6:36 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.
>>>
>>> Is that possible in kernel space.?
>>> --
>>
>>
>>
>> --
>> Regards,
>> Peter Teoh
>>
>
> --
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>



-- 
Regards,
Sandeep.





 	
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