linux-ext4 - Re: [PATCH] do not set extents feature from the kernel

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Date:	Mon, 07 Jul 2008 21:25:36 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Peng tao <bergwolf@...il.com>
CC:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] do not set extents feature from the kernel

Peng tao wrote:
> Hi, Eric
> 
> On Tue, Jul 8, 2008 at 4:15 AM, Eric Sandeen <sandeen@...hat.com> wrote:
>> We've talked for a while about getting rid of any feature-
>> setting from the kernel; this gets rid of the code which would
>> set the INCOMPAT_EXTENTS flag on the first file write when mounted
>> as ext4[dev].
>>
>> With this patch, if the extents feature is not already set on disk,
>> then mounting as ext4 will fall back to noextents with a warning,
>> and if -o extents is explicitly requested, the mount will fail,
>> also with warning.
> Does this mean no more migration from ext3 to ext4?

I think it just means you need to tune2fs -O extents before you can
mount as ext4 *with* extents.

.... which is, I guess, a bit of a convoluted story, but consistent with
"don't surprise users by setting incompat flags behind their back"

-Eric

>> Does this seem like a decent approach?
>>
>> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
>> ---
>>
>> Index: linux-2.6/fs/ext4/ialloc.c
>> ===================================================================
>> --- linux-2.6.orig/fs/ext4/ialloc.c     2008-07-07 10:22:00.000000000 -0500
>> +++ linux-2.6/fs/ext4/ialloc.c  2008-07-07 12:07:02.133292077 -0500
>> @@ -740,14 +740,10 @@ got:
>>                goto fail_free_drop;
>>
>>        if (test_opt(sb, EXTENTS)) {
>> -               /* set extent flag only for diretory, file and normal symlink*/
>> +               /* set extent flag only for directory, file and normal symlink*/
>>                if (S_ISDIR(mode) || S_ISREG(mode) || S_ISLNK(mode)) {
>>                        EXT4_I(inode)->i_flags |= EXT4_EXTENTS_FL;
>>                        ext4_ext_tree_init(handle, inode);
>> -                       err = ext4_update_incompat_feature(handle, sb,
>> -                                       EXT4_FEATURE_INCOMPAT_EXTENTS);
>> -                       if (err)
>> -                               goto fail_free_drop;
>>                }
>>        }
>>
>> Index: linux-2.6/fs/ext4/super.c
>> ===================================================================
>> --- linux-2.6.orig/fs/ext4/super.c      2008-07-07 10:22:19.000000000 -0500
>> +++ linux-2.6/fs/ext4/super.c   2008-07-07 14:08:43.684291817 -0500
>> @@ -1309,6 +1309,13 @@ set_qf_format:
>>                        clear_opt(sbi->s_mount_opt, NOBH);
>>                        break;
>>                case Opt_extents:
>> +                       if (!EXT4_HAS_INCOMPAT_FEATURE(sb,
>> +                                       EXT4_FEATURE_INCOMPAT_EXTENTS)) {
>> +                               ext4_warning(sb, __func__,
>> +                                       "extents feature not enabled "
>> +                                       "on this filesystem, use tune2fs\n");
>> +                               return 0;
>> +                       }
>>                        set_opt (sbi->s_mount_opt, EXTENTS);
>>                        break;
>>                case Opt_noextents:
>> @@ -1919,12 +1926,18 @@ static int ext4_fill_super (struct super
>>
>>        /*
>>         * turn on extents feature by default in ext4 filesystem
>> -        * User -o noextents to turn it off
>> +        * only if feature flag already set by mkfs or tune2fs.
>> +        * Use -o noextents to turn it off
>>         */
>> -       set_opt(sbi->s_mount_opt, EXTENTS);
>> +       if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_EXTENTS))
>> +               set_opt(sbi->s_mount_opt, EXTENTS);
>> +       else
>> +               ext4_warning(sb, __func__,
>> +                       "extents feature not enabled on this filesystem, "
>> +                       "use tune2fs.\n");
>>        /*
>> -        * turn on mballoc feature by default in ext4 filesystem
>> -        * User -o nomballoc to turn it off
>> +        * turn on mballoc code by default in ext4 filesystem
>> +        * Use -o nomballoc to turn it off
>>         */
>>        set_opt(sbi->s_mount_opt, MBALLOC);
>>
>>
>> --
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>>
> 
> 
> 

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