linux-kernel - Re: [PATCH 11/16] f2fs: add inode operations for special inodes

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Message-Id: <B1810D58-5211-4B91-A1D1-E907B9901C0D@dubeyko.com>
Date:	Sun, 14 Oct 2012 01:57:50 +0400
From:	Vyacheslav Dubeyko <slava@...eyko.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	김재극 <jaegeuk.kim@...sung.com>,
	viro@...iv.linux.org.uk, "'Theodore Ts'o'" <tytso@....edu>,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	chur.lee@...sung.com, cm224.lee@...sung.com,
	jooyoung.hwang@...sung.com
Subject: Re: [PATCH 11/16] f2fs: add inode operations for special inodes


On Oct 14, 2012, at 12:52 AM, Arnd Bergmann wrote:

> On Friday 05 October 2012, 김재극 wrote:
>> +const char *media_ext_lists[] = {
>> +       "jpg",
>> +       "gif",
>> +       "png",
>> +       "avi",
>> +       "divx",
>> +       "mp4",
>> +       "mp3",
>> ...
> 
>> + * Set multimedia files as cold files for hot/cold data separation
>> + */
>> +static inline void set_cold_file(struct inode *inode, const unsigned char *name)
>> +{
>> +       const char **extlist = media_ext_lists;
>> +
>> +       while (*extlist) {
>> +               if (!is_multimedia_file(name, *extlist)) {
>> +                       F2FS_I(inode)->is_cold = 1;
>> +                       break;
>> +               }
>> +               extlist++;
>> +       }
>> +}
> 
> This is a very clever way of categorizing files by their name, but I wonder if hardcoding
> the list of file name extensions at in the kernel source is the best strategy. Generally
> I would consider this to be a policy that should be configurable by the user.
> 

I think that file extensions can't be a steady basis for categorization. It is possible that user can use any extension as you want during file naming (for example, save text file with png extension). Or it is possible to use file without any extension. Only magics in a file structure can be a steady basis. But analyzing of file structure on the file system driver level is a breaking of some fundamentals, from my point of view.

With the best regards,
Vyacheslav Dubeyko.

> Unfortunately I can't think of a good interface to configure this, but maybe someone
> else has a useful idea. Maybe the list can be stored in the superblock and get written
> at mkfs time from the same defaults, but with the option of overriding it using
> a debugfs tool.
> 
> 	Arnd
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