Re: block allocation for ext2_mkdir

["Rohit Sharma" <imreckless@gmail.com>]

I am not sure but ext2_alloc_blocks function
in inode.c, allocate blocks for indirect blocks.



On Sat, Dec 20, 2008 at 12:19 AM, Rohit Sharma <imreckless@gmail.com> wrote:
> 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."
>>
>