From mboxrd@z Thu Jan 1 00:00:00 1970 To: =?gb2312?q?Song=20Sam?= Cc: linuxppc-embedded@lists.linuxppc.org Subject: Re: Cramfs Limitations From: Wolfgang Denk Mime-version: 1.0 Content-type: text/plain; charset=ISO-8859-1 In-reply-to: Your message of "Fri, 27 Aug 2004 09:35:50 +0800." <20040827013550.73877.qmail@web15605.mail.cnb.yahoo.com> Date: Fri, 27 Aug 2004 09:38:33 +0200 Message-Id: <20040827073838.E2DD9C109F@atlas.denx.de> Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: In message <20040827013550.73877.qmail@web15605.mail.cnb.yahoo.com> you wrote: > > > Are you really surprised that opening a file for > > writing fails on a read-only filesystem??? > > So only for this reason, I cannot choose Cramfs for my > application deployment??? Then I have nearly no other Why not? Of course you can. You just cannot write to it. > choice but use JFFS2 for deployment, which performance > couldn't compare with RAMDISK.It's a pity that RAMDISK > cannot update some info permanently. EXT2 seems not a You can use any filesystem, including one on a RAMDISK. If the root filesystem happens to be read-only, you just need to provide a writable filesystem for those things that need to get written. In case of data that may get lost at reboot you can use tmpfs, and for persistent storage you can use JFFS2. If you are concerned about updating individual files in your read-only filesystem (instead of updating the whole image (*)) you can use an overlay filesystem. For example, you can use "mini_fo" which was specifically tailored for such purposes; please see http://atlas.denx.de/denx/e/news.php#MINI_FO (*) Updating the whole image is not a bad idea - this way you can guarantee that all files int he image are really compatible with each other; keeping the system in a consisten state is much more difficult when individual files can get replaced at random. Best regards, Wolfgang Denk -- Software Engineering: Embedded and Realtime Systems, Embedded Linux Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd@denx.de "UNIX was not designed to stop you from doing stupid things, because that would also stop you from doing clever things." - Doug Gwyn ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/