From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ryan Mallon Subject: Re: [PATCH 08/16 v2] pramfs: headers Date: Tue, 09 Nov 2010 08:50:33 +1300 Message-ID: <4CD85489.8000503@bluewatersys.com> References: <4CD518C5.6000509@gmail.com> <4CD7076D.80507@bluewatersys.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Linux Kernel , Linux Embedded , Linux FS Devel , Tim Bird , Andrew Morton To: Marco Stornelli Return-path: In-Reply-To: Sender: linux-embedded-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On 11/08/2010 08:49 PM, Marco Stornelli wrote: > 2010/11/7 Ryan Mallon : >> On 11/06/2010 09:58 PM, Marco Stornelli wrote: >>> From: Marco Stornelli >>> >>> Definitions for the PRAMFS filesystem. >>> >>> Signed-off-by: Marco Stornelli >>> --- >>> diff -Nurp linux-2.6.36-orig/fs/pramfs/pram.h linux-2.6.36/fs/pramfs/pram.h >>> --- linux-2.6.36-orig/fs/pramfs/pram.h 1970-01-01 01:00:00.000000000 +0100 >>> +++ linux-2.6.36/fs/pramfs/pram.h 2010-10-30 12:02:45.000000000 +0200 >>> @@ -0,0 +1,317 @@ >> >>> +/* >>> + * Structure of the super block in PRAMFS >>> + */ >>> +struct pram_super_block { >>> + __be16 s_sum; /* checksum of this sb, including padding */ >>> + __be64 s_size; /* total size of fs in bytes */ >>> + __be32 s_blocksize; /* blocksize in bytes */ >>> + __be32 s_inodes_count; /* total inodes count (used or free) */ >>> + __be32 s_free_inodes_count;/* free inodes count */ >>> + __be32 s_free_inode_hint; /* start hint for locating free inodes */ >>> + __be32 s_blocks_count; /* total data blocks count (used or free) */ >>> + __be32 s_free_blocks_count;/* free data blocks count */ >>> + __be32 s_free_blocknr_hint;/* free data blocks count */ >>> + __be64 s_bitmap_start; /* data block in-use bitmap location */ >>> + __be32 s_bitmap_blocks;/* size of bitmap in number of blocks */ >>> + __be32 s_mtime; /* Mount time */ >>> + __be32 s_wtime; /* Write time */ >>> + __be16 s_magic; /* Magic signature */ >>> + char s_volume_name[16]; /* volume name */ >>> +}; >> >> Is there a particular reason to use big endian types for the data >> structures? On a little endian machine you will end up converting values >> everywhere. I assume that you don't expect the machine to change >> endianess between reboots :-). If this is for generating/reading >> filesystems from userspace, wouldn't it be better to have the userspace >> tools specify the target endianess and do the conversions there? >> >> ~Ryan > > Yes, there is a reason. In the first review a comment was: the fs must > have a fix endianess layout. This fs is designed for the embedded > world mainly. Since most of cpus used in this case are big-endian, it > means that for typical use case, there is no cost for endianess > conversion. ARM, which is a large portion of the embedded space, is typically little endian. Why does a filesystem need to have a specific endianess layout? Especially for a highly specialised filesystem like this. ~Ryan -- Bluewater Systems Ltd - ARM Technology Solution Centre Ryan Mallon 5 Amuri Park, 404 Barbadoes St ryan@bluewatersys.com PO Box 13 889, Christchurch 8013 http://www.bluewatersys.com New Zealand Phone: +64 3 3779127 Freecall: Australia 1800 148 751 Fax: +64 3 3779135 USA 1800 261 2934