Re: block allocation for ext2_mkdir

Rohit Sharma
2008-12-19T18:49:56Z

Is there a difference between how ext2 allocates block between
inode's indirect blocks and data blocks.

On Fri, Dec 19, 2008 at 8:59 PM, Peter Teoh <htmldeveloper@gmail.com> wrote:
> On Fri, Dec 19, 2008 at 7:18 PM, Rohit Sharma <imreckless@gmail.com> wrote:
>> On Fri, Dec 19, 2008 at 3:05 PM, Peter Teoh <htmldeveloper@gmail.com> wrote:
>>> On Fri, Dec 19, 2008 at 3:42 PM, Rohit Sharma <imreckless@gmail.com> wrote:
>>>> On Fri, Dec 19, 2008 at 4:09 AM, Jan Kara <jack@suse.cz> wrote:
>>>>>> On Fri, Dec 19, 2008 at 12:12 AM, Rohit Sharma <imreckless@gmail.com> wrote:
>>>>>> > How does ext2 allocate blocks for directory.
>>>>>> >
>>>>>> > ext2_mkdir calls ext2_make_empty
>>>>>> >
>>>>>> > ext2_make_empty calls __ext2_write_begin
>>>>>> >
>>>>>> > __ ext2_write_begin calls block_write_begin
>>>>>> >
>>>>>> > my query is that how does this function allocates blocks for directories. ??
>>>>>> >
>>>>>>
>>>>>> Does ext2 uses ext2_get_block to allocate blocks for both files and
>>>>>> directories. ??
>>>>> Yes, exactly. Ext2 (unlike ext3 or ext4) treats directories the same
>>>>> ways as ordinary files and thus ext2_get_block is used for block
>>>>> allocation.
>>>>>
>>>>
>>>> Can i modify this function to restrict allocation of blocks
>>>> to a particular block group ?
>>>>
>>>> Like i want that my abc.txt file should be in block group 5 suppose, then
>>>> what should i do?
>>>>
>>>
>>> I think this can be done. Or is done in the kernel source in several
>>> ways (indirectly).
>>>
>>> 1. ext2_find_goal()-->this will look for the best new block. when
>>> searching, it will try to find the block to be allocated to follow the
>>> one last allocated in the file, so as to maintain storage contiguity.
>>>
>>> 2. looking into fs/ext2/balloc.c: ext2_try_to_allocate(), there is a
>>> argument called group_goal, whose purpose is to specify the goal block
>>> group, and the algorithm will start searching from the group specified
>>> (look for "start=grp_goal"). Of course, if search is in vain it will
>>> proceed to other block group, which u don't want ....so may be can
>>> customize from here.
>>>
>>> Not sure if I am right?
>>>
>> When we create new file, do we use reservation window to allocate blocks
>> or we use reservation window every time we need a new data blocks
>> for file.
>>
>>
>
> http://lwn.net/Articles/81357/ ===> from here, we deduced that it
> should be done at every new block request level, and not at the file
> level. This is because when file level request is initiated, the
> first thing is see if any existing block can be reused or not, before
> allocating new block (which then comes with reservation features - to
> ensure contiguity of datablocks).
>
>
> --
> Regards,
> Peter Teoh
>
> Ernest Hemingway - "Never mistake motion for action."
>