From: "Rohit Sharma" Subject: Re: block allocation for ext2_mkdir Date: Sat, 20 Dec 2008 00:31:30 +0530 Message-ID: <2d08ef090812191101y11cb1448v78e207c0e885c8bf@mail.gmail.com> References: <2d08ef090812181042k2b15f27fke39076cc72453797@mail.gmail.com> <2d08ef090812181152r53fa9d18j1b21310c4e592f@mail.gmail.com> <20081218223928.GA20092@atrey.karlin.mff.cuni.cz> <2d08ef090812182342p1a210adcgd70d8a5cf3bf828c@mail.gmail.com> <804dabb00812190135q2cf1a5co85ce9cc4ac8bbb30@mail.gmail.com> <2d08ef090812190318w2c33c76bg93042ca61884cd5@mail.gmail.com> <804dabb00812190729r74d9f131kdd5c86d56320dc20@mail.gmail.com> <2d08ef090812191049p1da42e74jc9cce8f076a56ab7@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Jan Kara" , Kernelnewbies , ext4 To: "Peter Teoh" Return-path: Received: from wf-out-1314.google.com ([209.85.200.169]:59753 "EHLO wf-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750915AbYLSTBc (ORCPT ); Fri, 19 Dec 2008 14:01:32 -0500 Received: by wf-out-1314.google.com with SMTP id 27so1144781wfd.4 for ; Fri, 19 Dec 2008 11:01:30 -0800 (PST) In-Reply-To: <2d08ef090812191049p1da42e74jc9cce8f076a56ab7@mail.gmail.com> Content-Disposition: inline Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 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 wrote: >> On Fri, Dec 19, 2008 at 7:18 PM, Rohit Sharma wrote: >>> On Fri, Dec 19, 2008 at 3:05 PM, Peter Teoh wrote: >>>> On Fri, Dec 19, 2008 at 3:42 PM, Rohit Sharma wrote: >>>>> On Fri, Dec 19, 2008 at 4:09 AM, Jan Kara wrote: >>>>>>> On Fri, Dec 19, 2008 at 12:12 AM, Rohit Sharma 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." >> >