thumbnail mtime, ctime

[Thiago Macieira]

Dr. Michael J. Chudobiak wrote:
>>> Or your navigate to a folder, realize that you don't have read
>>> permission, so you fix it. But the thumbnail doesn't regenerate...
>>
>> I don't see that as a valid use-case. If the file can't be read, there
>> is no thumbnail. So what would you be storing in the thumbnail cache?
>
>A "failed" thumbnail is saved, as per the spec.
>http://people.freedesktop.org/~vuntz/thumbnail-spec-cache/failures.html.

Sorry for not seeing that before. Finding the spec isn't very easy. It's 
on the second page in Google search after you restrict to finding 
on "freedesktop.org" servers...

>The failed thumbnail stores the original mtime, so that system knows
>when to re-attempt thumbnailing. But since the ctime is not stored,
>permission fixing will not trigger a re-thumbnailing.
>
>It's a valid use case, in other words :-)

No, I don't agree.

I don't think a failed thumbnail should be saved under those conditions. 
The file isn't broken or unknown -- it simply could not be read. The 
reason for saving the negative cache is given in the spec: "Eg to avoid 
trying it again and again in the future."

But, in this case, failing to open a local file is *less* expensive than 
inspecting the negative cache (i.e.,, two failed open(2) calls, as 
opposed to a successful open(2) of the thumbnail, decoding the PNG data, 
extracting the Thumb::MTime attribute and then comparing to the mtime 
from stat(2) the target file). 

Remote files, however, I can't say. There are probably too many variables 
and differences in implementation.

So, my opinion is that the gnome bugzilla link you posted is a bug in 
Nautilus, not in the spec.

-- 
  Thiago Macieira  -  thiago (AT) macieira.info - thiago (AT) kde.org
    PGP/GPG: 0x6EF45358; fingerprint:
    E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
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