From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933541AbYD3Vxb (ORCPT ); Wed, 30 Apr 2008 17:53:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760442AbYD3VxW (ORCPT ); Wed, 30 Apr 2008 17:53:22 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:38090 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757024AbYD3VxW (ORCPT ); Wed, 30 Apr 2008 17:53:22 -0400 Date: Wed, 30 Apr 2008 14:53:11 -0700 From: Andrew Morton To: Andres Salomon Cc: cbou@mail.ru, linux-kernel@vger.kernel.org, dwmw2@infradead.org Subject: Re: [PATCH 2/4] power_supply: add eeprom dump file to olpc_battery's sysfs Message-Id: <20080430145311.a6c35ed7.akpm@linux-foundation.org> In-Reply-To: <20080430163008.4be68cb3@ephemeral> References: <20080430163008.4be68cb3@ephemeral> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 30 Apr 2008 16:30:08 -0400 Andres Salomon wrote: > > This allows you to dump 0x60 bytes from the battery's EEPROM (starting > at address 0x20). Note that it does an EC command for each byte, so > it's pretty slow. OTOH, if you want to grab just a single byte from > somewhere in the EEPROM, you can do something like: > > dd bs=1 count=1 skip=16 if=/sys/class/power_supply/olpc-battery/eeprom | od -x > > Userspace battery collection/logging information needs this. > > Signed-off-by: Andres Salomon > --- > drivers/power/olpc_battery.c | 49 ++++++++++++++++++++++++++++++++++++++++++ > 1 files changed, 49 insertions(+), 0 deletions(-) > > diff --git a/drivers/power/olpc_battery.c b/drivers/power/olpc_battery.c > index 9d9dd09..e5ecf27 100644 > --- a/drivers/power/olpc_battery.c > +++ b/drivers/power/olpc_battery.c > @@ -283,6 +283,48 @@ static enum power_supply_property olpc_bat_props[] = { > POWER_SUPPLY_PROP_SERIAL_NUMBER, > }; > > +/* EEPROM reading goes completely around the power_supply API, sadly */ > + > +#define EEPROM_START 0x20 > +#define EEPROM_END 0x80 > +#define EEPROM_SIZE (EEPROM_END - EEPROM_START) > + > +static ssize_t olpc_bat_eeprom_read(struct kobject *kobj, > + struct bin_attribute *attr, char *buf, loff_t off, size_t count) > +{ > + uint8_t ec_byte; > + int ret, end; > + > + if (off >= EEPROM_SIZE) > + return 0; loff_t is signed. Happily, the VFS prevents negative loff_t's from being passed into read() handlers. > + if (off + count > EEPROM_SIZE) > + count = EEPROM_SIZE - off; But the vfs doesn't check for (offset+len) going negative (I think?) However you got lucky (or smart ;)) - size_t is unsigned so the comparison will dtrt. Plus the first `if' will prevent us getting here with huge-nearly-negative `off'. This stuff is harder than it should be :(