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).
>
> --
> 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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