Re: Add --dereference option to df

[Pádraig Brady]

On 11/22/2013 01:52 AM, Pádraig Brady wrote:
> On 11/12/2013 07:45 AM, Bernhard Voelker wrote:
>> On 05/15/2013 04:39 PM, Pádraig Brady wrote:
>>> On 05/15/2013 03:32 PM, Ondrej Oprala wrote:
>>
>>>> Let me explain by example from my system:
>>>>
>>>> /dev/sda1 is mounted on /boot
>>>> /dev/disk/by-uuid/37a5c8d4-78ff-408f-8ae8-70555df51f7f is a symlink to 
>>>> /dev/sda1
>>>>
>>>> #in the following example df prints info about the fs where the symlink 
>>>> file is.
>>>> $ df /dev/disk/by-uuid/37a5c8d4-78ff-408f-8ae8-70555df51f7f
>>>> Filesystem     1K-blocks  Used Available Use% Mounted on
>>>> devtmpfs         1013888     0   1013888   0% /dev
>>>>
>>>> #with -L, information about the symlinked FS is printed.
>>>> $ df -L /dev/disk/by-uuid/37a5c8d4-78ff-408f-8ae8-70555df51f7f
>>>> Filesystem     1K-blocks  Used Available Use% Mounted on
>>>> /dev/sda1        1013888     0   1013888   0% /boot
>>>>
>>>> So although the argument is stat-ed(dereferenced) in both cases, different 
>>>> parts
>>>> of the information are used to decide what to output if -L is specified 
>>>> (which is why
>>>> I find the option name misleading).
>>>
>>> Ah /dev/sda1 (/boot) isn't mounted on my system
>>> (as I don't want that disk spinning up (long story)).
>>> That's why I got the results I presented.
>>> More thinking required...
>>
>> Isn't that what the findmnt(8) command achieves with
>> the -S,--source option, i.e. it's not only about dereferencing
>> per se but rather telling the tool that we're searching for
>> the source of a mount instead of the target?
>>
>> Therefore, I think making the changes in get_point() is abusing the
>> semantics of that function.  Instead, get_disk() should be enhanced
>> in a similar way as in get_point() via canonicalize_file_name().
> 
> Makes sense.
> 
>> Another question is if such behavior could/should be made the default
>> or if a new option has to be introduced.
> 
> I'd make it default to dereference. No new options needed I think.

This would be appropriate for the imminent release I think.
I'll have a look later if you've no time.

thanks,
Pádraig.