Re: [PATCH 2/4] power_supply: add eeprom dump file to olpc_battery's sysfs

On Wed, 30 Apr 2008 16:30:08 -0400
Andres Salomon <dilinger@xxxxxxxxxx> 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@xxxxxxxxxx>
---
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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