[PATCH 2/2] i2c-tools: fix build with upstream i2c-tools' headers

[Bartosz Gołaszewski]

2017-08-28 15:48 GMT+02:00 Denys Vlasenko <vda.linux at googlemail.com>:
> On Mon, Aug 28, 2017 at 11:49 AM, Bartosz Golaszewski
> <bartekgola at gmail.com> wrote:
>> Installing headers from upstream i2c-tools makes it impossible to
>> build the busybox version due to redefined symbols. This is caused by
>> the fact that linux/i2c-dev.h from i2c-tools overwrites the one from
>> linux uapi and defines symbols already defined by linux' linux/i2c.h.
>>
>> Fix it by including linux/i2c.h and defining the i2c access routines
>> only if a well known symbol provided by linux uapi is not defined in
>> linux/i2c-dev.h.
>>
>> Tested by building on systems with and without i2c-tools headers.
>>
>> Signed-off-by: Bartosz Golaszewski <bartekgola at gmail.com>
>> ---
>>  miscutils/i2c_tools.c | 16 +++++++++++++++-
>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/miscutils/i2c_tools.c b/miscutils/i2c_tools.c
>> index 03a09d519..9cc55eb27 100644
>> --- a/miscutils/i2c_tools.c
>> +++ b/miscutils/i2c_tools.c
>> @@ -62,7 +62,6 @@
>>
>>  #include "libbb.h"
>>
>> -#include <linux/i2c.h>
>>  #include <linux/i2c-dev.h>
>>
>>  #define I2CDUMP_NUM_REGS               256
>> @@ -79,6 +78,19 @@ static ALWAYS_INLINE void *itoptr(int i)
>>         return (void*)(intptr_t)i;
>>  }
>>
>> +/*
>> + * Only include linux/i2c.h if the symbols provided by it are not already
>> + * defined in linux/i2c-dev.h. This - while not correct - happens if we
>> + * install the headers provided by upstream i2c-tools and is the default on
>> + * some distributions (Debian, OpenSUSE). linux/i2c-dev.h from i2c-tools
>> + * overwrites the linux uapi header and redefines a bunch of symbols, as
>> + * well as already provides the i2c access functions we redefine below.
>
> Oh boy. They have "static inlines" there, right?
> That would add some hundreds of bytes of code.
>
> Maybe we should drop "#include <linux/i2c-dev.h>" instead?
>
> What are we using from those, "struct i2c_smbus_ioctl_data"
> and "struct i2c_rdwr_ioctl_data" only?

Just removing this include is giving me this:

  CC      miscutils/i2c_tools.o
miscutils/i2c_tools.c: In function ‘i2c_smbus_access’:
miscutils/i2c_tools.c:86:30: error: storage size of ‘args’ isn’t known
  struct i2c_smbus_ioctl_data args;
                              ^~~~
miscutils/i2c_tools.c:93:19: error: ‘I2C_SMBUS’ undeclared (first use
in this function)
  return ioctl(fd, I2C_SMBUS, &args);
                   ^~~~~~~~~
miscutils/i2c_tools.c:93:19: note: each undeclared identifier is
reported only once for each function it appears in
miscutils/i2c_tools.c:86:30: warning: unused variable ‘args’ [-Wunused-variable]
  struct i2c_smbus_ioctl_data args;
                              ^~~~
miscutils/i2c_tools.c: In function ‘i2c_set_pec’:
miscutils/i2c_tools.c:258:30: error: ‘I2C_PEC’ undeclared (first use
in this function)
  ioctl_or_perror_and_die(fd, I2C_PEC,
                              ^~~~~~~
miscutils/i2c_tools.c: In function ‘i2c_set_slave_addr’:
miscutils/i2c_tools.c:265:38: error: ‘I2C_SLAVE_FORCE’ undeclared
(first use in this function)
  ioctl_or_perror_and_die(fd, force ? I2C_SLAVE_FORCE : I2C_SLAVE,
                                      ^~~~~~~~~~~~~~~
miscutils/i2c_tools.c:265:56: error: ‘I2C_SLAVE’ undeclared (first use
in this function)
  ioctl_or_perror_and_die(fd, force ? I2C_SLAVE_FORCE : I2C_SLAVE,
                                                        ^~~~~~~~~
miscutils/i2c_tools.c: In function ‘get_funcs_matrix’:
miscutils/i2c_tools.c:307:30: error: ‘I2C_FUNCS’ undeclared (first use
in this function)
  ioctl_or_perror_and_die(fd, I2C_FUNCS, funcs,
                              ^~~~~~~~~
miscutils/i2c_tools.c: In function ‘i2cdetect_main’:
miscutils/i2c_tools.c:1304:23: error: ‘I2C_SLAVE’ undeclared (first
use in this function)
    status = ioctl(fd, I2C_SLAVE, itoptr(i + j));
                       ^~~~~~~~~
miscutils/i2c_tools.c: In function ‘i2c_smbus_access’:
miscutils/i2c_tools.c:94:1: warning: control reaches end of non-void
function [-Wreturn-type]
 }

I can play a bit with it and see if we can drop this file while not
re-writing the whole header.

-- 
Best regards,
Bartosz Golaszewski