Re: [PATCH v2] ieee1275: obdisk driver

[Eric Snowberg]

> On Sep 1, 2018, at 11:10 AM, Daniel Kiper <address@hidden> wrote:
> 
> On Thu, Aug 30, 2018 at 09:28:52AM -0600, Eric Snowberg wrote:
>>> On Aug 30, 2018, at 8:06 AM, Daniel Kiper <address@hidden> wrote:
>>> On Tue, Jul 17, 2018 at 09:59:33AM -0600, Eric Snowberg wrote:
>>>>> On Jul 17, 2018, at 7:38 AM, Daniel Kiper <address@hidden> wrote:
>>>>> On Mon, Jul 16, 2018 at 09:33:17AM -0600, Eric Snowberg wrote:
>>>>>>> On Jul 16, 2018, at 7:51 AM, Daniel Kiper <address@hidden> wrote:
>>>>>>> 
>>>>>>> Sorry for late reply but I was busy with other stuff.
>>>>>>> 
>>>>>>> On Thu, Jun 21, 2018 at 01:46:46PM -0600, Eric Snowberg wrote:
>>>>>>>>> On Jun 21, 2018, at 10:58 AM, Daniel Kiper <address@hidden> wrote:
>>>>>>>>> On Fri, Jun 15, 2018 at 09:58:56AM -0600, Eric Snowberg wrote:
>>>>>>>>>>> On Jun 15, 2018, at 6:02 AM, Daniel Kiper <address@hidden> wrote:
>>>>>>>>>>> On Wed, May 30, 2018 at 04:55:22PM -0700, Eric Snowberg wrote:
>>>>>>> 
>>>>>>> [...]
>>>>>>> 
>>>>>>>>>>>> +static char *
>>>>>>>>>>>> +replace_escaped_commas (char *src)
>>>>>>>>>>>> +{
>>>>>>>>>>>> +  char *iptr;
>>>>>>>>>>>> +
>>>>>>>>>>>> +  if (src == NULL)
>>>>>>>>>>>> +    return NULL;
>>>>>>>>>>>> +  for (iptr = src; *iptr; )
>>>>>>>>>>>> +    {
>>>>>>>>>>>> +      if ((*iptr == '\\') && (*(iptr + 1) == ','))
>>>>>>>>>>>> +        {
>>>>>>>>>>>> +          *iptr++ = '_';
>>>>>>>>>>>> +          *iptr++ = '_';
>>>>>>>>>>>> +        }
>>>>>>>>>>>> +      iptr++;
>>>>>>>>>>>> +    }
>>>>>>>>>>>> +
>>>>>>>>>>>> +  return src;
>>>>>>>>>>>> +}
>>>>>>>>>>>> +
>>>>>>>>>>>> +static int
>>>>>>>>>>>> +count_commas (const char *src)
>>>>>>>>>>>> +{
>>>>>>>>>>>> +  int count = 0;
>>>>>>>>>>>> +
>>>>>>>>>>>> +  for ( ; *src; src++)
>>>>>>>>>>>> +    if (*src == ',')
>>>>>>>>>>>> +      count++;
>>>>>>>>>>>> +
>>>>>>>>>>>> +  return count;
>>>>>>>>>>>> +}
>>>>>>>>>>>> +
>>>>>>>>>>>> +static void
>>>>>>>>>>>> +escape_commas (const char *src, char *dest)
>>>>>>>>>>> 
>>>>>>>>>>> I am confused by this play with commas. Could explain somewhere
>>>>>>>>>>> where this commas are needed unescaped, escaped, replaced, etc.
>>>>>>>>>>> Could not we simplify this somehow?
>>>>>>>>>> 
>>>>>>>>>> I’m open for recommendations.
>>>>>>>>> 
>>>>>>>>> Great! However, I need more info which layer need what WRT ",”,
>>>>>>>> 
>>>>>>>> AFAIK all layers above expect it:
>>>>>>>> https://www.gnu.org/software/grub/manual/grub/grub.html#Device-syntax
>>>>>>>> 
>>>>>>>> Everything above this driver expects it to be escaped.  Obviously when
>>>>>>> 
>>>>>>> Do you mean from the command line?
>>>>>> 
>>>>>> This goes much further than the command line.  For example, it is
>>>>>> built right into the disk driver.  Look at grub-core/kern/disk.c: 544
>>>>> 
>>>>> This is the last line of the file. So, I am not sure what exactly you 
>>>>> mean.
>>>>> 
>>>>>> /* Return the location of the first ',', if any, which is not
>>>>>> escaped by a '\'.  */
>>>>>> static const char *
>>>>>> find_part_sep (const char *name)
>>>>>> {
>>>>>> const char *p = name;
>>>>>> char c;
>>>>>> 
>>>>>> while ((c = *p++) != '\0')
>>>>>>  {
>>>>>>    if (c == '\\' && *p == ',')
>>>>>>      p++;
>>>>>>    else if (c == ',')
>>>>>>      return p - 1;
>>>>>>  }
>>>>>> return NULL;
>>>>>> }
>>>>> 
>>>>> OK, this one.
>>>>> 
>>>>>> When the obdisk driver discovers a disk, it must put the disk name in
>>>>>> the proper format.  Otherwise when grub_disk_open takes place later
>>>>>> on, the wrong disk name will eventually get sent back to the obdisk
>>>>>> driver.
>>>>> 
>>>>> Then we need proper escaping. And AIUI your driver does that.
>>>>> 
>>>>>>> If yes could you give an example with
>>>>>>> proper escaping?
>>>>>>> 
>>>>>>>> the driver talks to the actual hardware these devices can not have the
>>>>>>>> escaped names.
>>>>>>> 
>>>>>>> OK but this is not clear. So, please add a comment explaining it in
>>>>>>> the code somewhere.
>>>>>> 
>>>>>> Ok
>>>>>> 
>>>>>>> 
>>>>>>>>> how often this conversions must be done, why you have chosen that
>>>>>>>>> solution, etc. Then I will try to optimize solution a bit.
>>>>>>>> 
>>>>>>>> Under normal circumstances it only takes place once per disk as they
>>>>>>>> are enumerated.   All disks are cached within this driver so it should
>>>>>>>> not happen often.  That is why I store both versions so I don’t have
>>>>>>>> to go back and forth.  Look at the current driver ofdisk.  It has a
>>>>>>>> function called compute_dev_path which does this conversion on every
>>>>>>>> single open (grub_ofdisk_open).  That does not happen with this new
>>>>>>>> driver.  IMHO this is a much more optimized solution than the current
>>>>>>>> driver.
>>>>>>> 
>>>>>>> Then OK. However, this have to be explained somewhere in the code.
>>>>>>> Additionally, I think that proper variable naming would help too,
>>>>>>> e.g. name and name_esc. And I would do this:
>>>>>>> - s/decode_grub_devname/unescape_grub_devnam/,
>>>>>>> - s/encode_grub_devname/escape_grub_devname/,
>>>>>> 
>>>>>>> - extract unscaping code to the unescape_commas() function;
>>>>>>> even if it is called once; just for the completeness.
>>>>>> 
>>>>>> Ok
>>>>>> 
>>>>>>> 
>>>>>>> What is replace_escaped_commas()? Why do we need that function?
>>>>>> 
>>>>>> It is a convenience function for the end-user, so they can access a
>>>>>> disk without having to understand all this escaping when they want to
>>>>>> use one thru the shell.
>>>>> 
>>>>> I think that this will introduce more confusion. I would like that
>>>>> escaping of drive paths should be properly explained in GRUB docs.
>>>>> Including why it is needed. And replace_escaped_commas() should be
>>>>> dropped.
>>>> 
>>>> The confusion seems to be around what needs to be escaped and what
>>>> doesn’t, as can be seen from the discussion within this email. This
>>>> change makes it convenient for the end-user, since they will not need
>>>> to understand any of this.
>>>> 
>>>> When function grub_obdisk_iterate (defined as .iterate within
>>>> grub_disk_dev) gets called, it returns the disks the driver controls.
>>>> As explained within the description of this patch, a single IEEE1275
>>>> disk can have over 6 names.  When the .iterate function is called,
>>>> only a single drive can be returned.  If the disk that is to be
>>>> returned contains \\, within the name, they are replaced with __.
>>>> Then for example, the end-user will see something like this following
>>>> a ls:
>>>> 
>>>> grub> ls
>>>> (ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden)
>>>>  (ieee1275//address@hidden/pc
>>>> address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,gpt1)
>>>>  (ieee1275//address@hidden/address@hidden/address@hidden
>>>> /address@hidden) 
>>>> (ieee1275//address@hidden/address@hidden/address@hidden/address@hidden,gpt3)
>>>>  (ieee1275//pc
>>>> address@hidden/address@hidden/address@hidden/address@hidden,gpt2) 
>>>> (ieee1275//address@hidden/address@hidden/address@hidden/
>>>> address@hidden,gpt1)
>>>> 
>>>> The end-user can now type the disk name exactly as it is returned on
>>>> the screen.  Or they can escape any of the real disk names properly
>>>> and the driver will understand it is the same disk.  Do you really
>>>> want this removed?
>>> 
>>> After some thinking it seems to me that we should remove this "__"
>>> feature. It introduces another specific escaping form. And IMO this will
>>> make more confusion then it is worth. And what if disk path contains
>>> "__”? Yeah, I know probably it is not the case right now but we should
>>> be prepared…
>>> Though I am not against displaying properly escaped
>>> disks and partitions paths, e.g.:
>>> 
>>> (ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,0)
>>> 
>>> or
>>> 
>>> (ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,0,gpt1)
>>> 
>>> etc.
>> 
>> I don’t believe you have escaped the name properly above.  Unless you
>> are suggesting substituting ‘\\’ with “\\” before the item is
> 
> I think that it is correct. If you use one '\' then after shell
> processing you will get
> 
> (ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,0)
> 
> or
> 
> (ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,0,gpt1)
> 
> And I suppose that this is not what you want. So, you need two '\'.
> This way the layer below will get after shell processing
> 
> (ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,0)
> 
> or
> 
> (ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,0,gpt1)
> 
> Then new driver should get
> 
> ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,0
> 
> or
> 
> ieee1275//address@hidden/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden,0
> 
> if you really need escaped ',' in the path.

For obdisk devices that are displayed thru the shell, I didn't want the escaped 
‘,’ in the path.  But you rejected my change that substituted it with __ 
instead.  Therefore we are left with making this work with code above obdisk 
without changing it.

> However, I do not think so.
> It seems to me that OF expects ',' as ','. Hence, I have a feeling that
> we can reduce number of escaping/unescaping in the driver.
> 
> Am I right?

No.

The driver provides the name of the device which is displayed in the shell. It 
must be in a format that will allow it to get back to the driver at a later 
time.  If a ‘,’ is in the name, it must be escaped. Otherwise the code above 
the driver will trim off everything to the right of the ‘,’. Then the driver 
will be sent a device name that does not exist.  

For example with this device:
/address@hidden/address@hidden/LSI,address@hidden/address@hidden,0,gpt3

If the ‘,’ is not escaped properly, either (obdisk or ofdisk) will be sent an 
open to device: /address@hidden/address@hidden/LSI.  The upper level code will 
think everything to the right of the ‘,’ is the partition.  Once the driver 
receives this open, it will fail, since it isn’t a valid device.