Subject: Re: bug#10363: df vs. long-named /dev/disk/by-uuid/... file system device names

From: Pádraig Brady <[email-masked]>
Date: Mon, 02 Jan 2012 19:27:20 +0000

On 01/02/2012 05:34 PM, Jim Meyering wrote:
> Jim Meyering wrote:
> ...
>> +  char *dev_name = xstrdup (disk);
>> +  char *resolved_dev;
>> +
>> +  /* On some systems, dev_name is a long-named symlink like
>> +     /dev/disk/by-uuid/828fc648-9f30-43d8-a0b1-f7196a2edb66 pointing
>> +     to a much shorter and more useful name like /dev/sda1.
>> +     When process_all is true and dev_name is a symlink whose name starts
>> +     with /dev/disk/by-uuid/ use the resolved name instead.  */
>> +  if (process_all
>> +      && STRPREFIX (dev_name, "/dev/disk/by-uuid/")
>> +      && (resolved_dev = canonicalize_filename_mode (dev_name, CAN_EXISTING)))
>> +    {
>> +      free (dev_name);
>> +      dev_name = resolved_dev;
>> +    }
> 
> I noticed that there is a similar problem on any recent
> system with an encrypted root partition.
> In that case, the kernel is booted with an argument like this
> 
>     root=/dev/mapper/luks-88888888-8888-8888-8888-888888888888
> 
> and that same name appears in /proc/mounts and thus, even with
> the proposed patch, in df's "Filesystem" column.  The knee-jerk
> reaction is to do this:
> 
>      if (process_all
>          && (STRPREFIX (dev_name, "/dev/disk/by-uuid/")
>              || STRPREFIX (dev_name, "/dev/mapper/luks-"))
>          && (resolved_dev = canonicalize_filename_mode (dev_name, CAN_EXISTING)))
> 
> but will the prefix always be spelled that way?
> 
> Now, I'm thinking about making this a little more future-proof by
> matching the UUID part /[0-9a-fA-F-]{36}$/ instead.
> I.e., testing something like this:
> 
>      if (process_all
>          && has_uuid_suffix (dev_name)
>          && (resolved_dev = canonicalize_filename_mode (dev_name, CAN_EXISTING)))
> 
> using this new function:
> 
>   static bool
>   has_uuid_suffix (char const *s)
>   {
>     size_t len = strlen (s);
>     return (36 < len
>             && strspn (s + len - 36, "-0123456789abcdefABCDEF") == 36);
>   }

Yes that's awkward but warranted.
The logic looks correct.

This is assuming of course that UUIDs are the only "high level" form
presented in /proc/mounts that one doesn't want displayed.
I can't think of anything else worth avoiding at the moment.

cheers,
Pádraig.