Re: [PATCH] log replay should not overwrite newer ondisk inodes

[Lachlan McIlroy <lachlan@sgi.com>]

Timothy Shimmin wrote:
> Lachlan McIlroy wrote:
>> Log replay of clustered inodes currently ignores the flushiter
>> field in the inode that is used to determine if the on-disk inode
>> is more up to date than the copy in the log.  As a result during
>> log replay the newer inode is being overwritten with an older
>> version and file size updates are being lost.
>>
>> I haven't handled the case of the flushiter counter overflowing
>> but that shouldn't be a problem in this case.  The log buffer
>> contains newly created inodes so their flushiter values will be 0
>> and the on-disk inodes should not be much greater.
>>
>> Lachlan
>>
> 
> Still would want to understand why blf_flags doesn't have
> XFS_BLI_INODE_ALLOC_BUF set and so we could test that
> - I didn't understand Dave's (dgc) response about that earlier.
> But anyway...:)
> 
> 
> Just some nit-picks:
> 
> * instead of a comment and then calling xfs_recover_inode
>   why don't we just give the function a better name.
>   When I see the name I think it is going to recover the inode
>   but instead it is just a flush_iter check and matching
>   the magic#s.
What would you like the function to be called?

> 
> * My style preference is for option 2 over option 1:
>   1.
>     if (a) {
>        return 1;
>     }
>     return 0;
> 
>   2.
>     return a;
> 
>   But I understand the predicate is long and sometimes people like
>   to add tracing/debug for the alternate paths in which case (1)
>   is handy for that. I just like simplicity.
I can change that.  It just looks odd when the body of the function
is after the return statement.

> 
> * Also it is funny to return a boolean for error in the call.
>   Although, I see that is consistent with the rest of the function.
Yep, keeping consistent with coding standards.

>   But I'm not sure this is an error...
>   Hmmmm...I'm a bit confused.
>   So you are _almost_ combining an error check with a flushiter check?
>   If one buffer is an inode magic# and the other isn't then we
>   have an error right - and could report it - but we are not doing that 
> here.
Not exactly.  If what's on disk is not an inode but the log item is
then that could be because we haven't written the inode to disk yet
and we need to perform recovery.  If what's on disk is an inode but
the log item is not an inode then what we are about to recover is not
an inode and we abort the check.  If neither on-disk nor log item are
inodes then we've got no business continuing the check.

>   If we have an inode buf and the flushiter on the item is older than 
> the ondisk buffer
>   one then it is not an error but we just don't want to recover it.
Exactly.

> 
> 
> 
> --Tim
> 
> 
> --- fs/xfs/xfs_log_recover.c_1.322    2007-08-27 17:45:45.000000000 +1000
> +++ fs/xfs/xfs_log_recover.c    2007-08-30 11:50:44.000000000 +1000
> @@ -1866,6 +1866,27 @@ xlog_recover_do_inode_buffer(
>  }
> 
>  /*
> + * Check if we need to recover an inode from a buffer
> + */
> +int
> +xfs_recover_inode(
> +    char    *dest,
> +    char    *src)
> +{
> +    xfs_dinode_t    *dip = (xfs_dinode_t *)dest;
> +    xfs_dinode_t    *dilp = (xfs_dinode_t*)src;
> +
> +    if ((be16_to_cpu(dip->di_core.di_magic) == XFS_DINODE_MAGIC) &&
> +        (be16_to_cpu(dilp->di_core.di_magic) == XFS_DINODE_MAGIC) &&
> +        (be16_to_cpu(dilp->di_core.di_flushiter) <
> +            be16_to_cpu(dip->di_core.di_flushiter))) {
> +        return 1;
> +    }
> +
> +    return 0;
> +}
> +
> +/*
>   * Perform a 'normal' buffer recovery.  Each logged region of the
>   * buffer should be copied over the corresponding region in the
>   * given buffer.  The bitmap in the buf log format structure indicates
> @@ -1917,6 +1938,13 @@ xlog_recover_do_reg_buffer(
>                             -1, 0, XFS_QMOPT_DOWARN,
>                             "dquot_buf_recover");
>          }
> +        /*
> +         * Sanity check if this is an inode buffer.
> +         */
> +        if (!error)
> +            error = xfs_recover_inode(xfs_buf_offset(bp,
> +                    (uint)bit << XFS_BLI_SHIFT),
> +                    item->ri_buf[i].i_addr);
>          if (!error)
>              memcpy(xfs_buf_offset(bp,
>                  (uint)bit << XFS_BLI_SHIFT),    /* dest */
> 
>