linux-ext4 - Re: [PATCH -v3] ext4: implementation of a new ioctl called EXT4_IOC_SWAP

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Message-Id: <9E765F01-4954-4182-91F5-8E1F476720CC@dilger.ca>
Date:	Sun, 7 Apr 2013 15:29:03 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Theodore Ts'o <tytso@....edu>
Cc:	"Dr. Tilmann Bubeck" <t.bubeck@...nform.de>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH -v3] ext4: implementation of a new ioctl called EXT4_IOC_SWAP_BOOT

On 2013-04-07, at 13:48, Theodore Ts'o <tytso@....edu> wrote:
> On Sun, Apr 07, 2013 at 11:09:58AM -0600, Andreas Dilger wrote:
>>> +    if (inode_bl->i_nlink == 0) {
>>> +        /* this inode has never been used as a BOOT_LOADER */
>>> +        set_nlink(inode_bl, 1);
>>> +        i_uid_write(inode_bl, 0);
>>> +        i_gid_write(inode_bl, 0);
>>> +        inode_bl->i_flags = 0;
>>> +        ei_bl->i_flags = 0;
>>> +        inode_bl->i_version = 1;
>>> +        i_size_write(inode_bl, 0);
>>> +        inode_bl->i_mode = S_IFREG;
>>> +        if (EXT4_HAS_INCOMPAT_FEATURE(sb,
>>> +                          EXT4_FEATURE_INCOMPAT_EXTENTS)) {
>>> +            ext4_set_inode_flag(inode_bl, EXT4_INODE_EXTENTS);
>>> +            ext4_ext_tree_init(handle, inode_bl);
>>> +        } else
>>> +            memset(ei_bl->i_data, 0, sizeof(ei_bl->i_data));
>> 
>> I don't understand this. Wouldn't this clobber the block pointers if 
>> an existing boot inode and cause them to leak?  This seems broken to me. 
> 
> If i_nlink is zero, then there is no existing boot loader inode.  In
> theory the rest of the inode is zero, but this is to make sure the
> inode is initialized to something sane before we swap it into the
> user-visible inode.

Oh, my bad. I thought the else was for the nlink != 0 case, not the !extent case (the danger of reading email on my phone, I guess). Looks fine. 

> 

Cheers, Andreas--
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