On Sun, Dec 21, 2008 at 10:50 AM, Sandeep K Sinha
<sandeepksinha@xxxxxxxxx> wrote:
> Thanks a lot Peter for taking out time and looking into the issue at
> such a deeper level.
>
> Thanks again,
>
>
> On Sun, Dec 21, 2008 at 6:48 AM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote:
>> On Sat, Dec 20, 2008 at 3:18 AM, Rohit Sharma <imreckless@xxxxxxxxx> wrote:
>>> in ext2/balloc.c
>>> i saw a function ext2_new_blocks()
>>> its the core function to allocate blocks, it has been specified there.
>>>
>>> So all the blocks that are allocated in the file system is through
>>> this function only ,
>>> am i correct ?
>>
>> In this ext2_new_blocks() function, between retry_alloc: and the
>> allocated: symbol:
>>
>> retry_alloc:
>> gdp = ext2_get_group_desc(sb, group_no, &gdp_bh);
>> if (!gdp)
>> goto io_error;
>>
>> free_blocks = le16_to_cpu(gdp->bg_free_blocks_count);
>> /*
>> <snip>
>> <snip>
>>
>> /*
>> * We may end up a bogus ealier ENOSPC error due to
>> * filesystem is "full" of reservations, but
>> * there maybe indeed free blocks avaliable on disk
>> * In this case, we just forget about the reservations
>> * just do block allocation as without reservations.
>> */
>> if (my_rsv) {
>> my_rsv = NULL;
>> windowsz = 0;
>> group_no = goal_group;
>> goto retry_alloc;
>> }
>> /* No space left on the device */
>> *errp = -ENOSPC;
>> goto out;
>>
>> allocated:
>>
>> It seemed that you can copy the chunk and modify it to your
>> requirement - which is to allocate only from a particular block group.
>> And you have also to modify it so that if the group_no is not
>> available anymore than ENOSPC must be returned.
>>
>> But then this is too low level.
>>
>> Reading Documentation/filesystem/ext2.txt, it says that:
>>
>> "The inode allocation code tries to assign inodes which are in the same
>> block group as the directory in which they are first created."
>>
>> So if you create an API that create a directory in a particular block
>> group, and then let the file be created naturally, it should end up in
>> the same block group. Just create the file, and check the inode
>> later. If it is not in the same block group, most likely u have run
>> out of space within the block group.
>>
>> Modify at the highest possible ext2 level (API specified in
>> ext2_file_operations, and ext2_dir_operations).
>>
At higher level , we are using the following functions.
These can restrict inode allocation to a particular block group.
find_group_dir()
find_group_orlov()
find_group_other()
and for allocating data blocks for an inode
we can use
ext2_find_near()
ext2_find_goal()
Tell me if i can use some other functions for the purpose.
>> --
>> Regards,
>> Peter Teoh
>>
>> Ernest Hemingway - "Never mistake motion for action."
>>
>> --
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>>
>>
>
>
>
> --
> Regards,
> Sandeep.
>
>
>
>
>
>
> "To learn is to change. Education is a process that changes the learner."
>
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