From: "Rohit Sharma" Subject: Re: block allocation for ext2_mkdir Date: Fri, 19 Dec 2008 16:48:33 +0530 Message-ID: <2d08ef090812190318w2c33c76bg93042ca61884cd5@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> 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 ([209.85.200.168]:41223 "EHLO wf-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752250AbYLSLSe (ORCPT ); Fri, 19 Dec 2008 06:18:34 -0500 Received: by wf-out-1314.google.com with SMTP id 27so962399wfd.4 for ; Fri, 19 Dec 2008 03:18:33 -0800 (PST) In-Reply-To: <804dabb00812190135q2cf1a5co85ce9cc4ac8bbb30@mail.gmail.com> Content-Disposition: inline Sender: linux-ext4-owner@vger.kernel.org List-ID: 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. > -- > Regards, > Peter Teoh > > Ernest Hemingway - "Never mistake motion for action." >