Messages in this thread | | | Date | Wed, 30 Apr 2008 14:53:11 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 2/4] power_supply: add eeprom dump file to olpc_battery's sysfs |
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On Wed, 30 Apr 2008 16:30:08 -0400 Andres Salomon <dilinger@queued.net> 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 <dilinger@debian.org> > --- > 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 :(
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