Re: [PATCH] Introduce SEEK_DATA/SEEK_HOLE support V8

Jeff Liu
2012-05-10T02:51:31Z

On 05/10/2012 01:42 AM, Mark Tinguely wrote:

> On 02/17/12 07:16, Jeff Liu wrote:
>> Hello,
>>
>> This is the revised patch according to Dave's comments for V7.
>>
>> Changes to V8:
>> --------------
>> 1. If there is an internal error raised at extent reading routine, just
>> return it rather than ENXIO.
>> 2. Add the commit message.
>> 3. Remove the for(;;) loop since there is no continuous holes shown even
>> if create a Petabyte sparse file with hole extent length longer than
>> 32-bit. Thanks Dave for helping verify that!
>> 4. In xfs_seek_data(), s/len/end/, looks 'end' is more meaningful here
>> to indicate the range of extents mapped.
>> 5. Remove BUG() from xfs_seek_data() since xfs_bmapi_read() have found
>> any corruption during the lookup, it should not occurred at all.
>>
>> Any comments are appreciated!
>>
>> Thanks,
>> -Jeff
>>
>>
>> Signed-off-by: Jie Liu<jeff.liu@oracle.com>
>> ---
>> This patch adds lseek(2) SEEK_DATA/SEEK_HOLE functionality.
>
>> +STATIC loff_t
>> +xfs_seek_hole(
>> + struct file *file,
>> + loff_t start,
>> + u32 type)
>> +{
>> + struct inode *inode = file->f_mapping->host;
>> + struct xfs_inode *ip = XFS_I(inode);
>> + struct xfs_mount *mp = ip->i_mount;
>> + loff_t uninitialized_var(offset);
>> + loff_t holeoff;
>> + xfs_fsize_t isize;
>> + xfs_fileoff_t fsbno;
>> + uint lock;
>> + int error;
>> +
>> + lock = xfs_ilock_map_shared(ip);
>> +
>> + isize = i_size_read(inode);
>> + if (start>= isize) {
>> + error = ENXIO;
>> + goto out_unlock;
>> + }
>> +
>> + fsbno = XFS_B_TO_FSBT(mp, start);
>> + error = xfs_bmap_first_unused(NULL, ip, 1,&fsbno, XFS_DATA_FORK);
>> + if (error)
>> + goto out_unlock;
>> +
>> + holeoff = XFS_FSB_TO_B(mp, fsbno);
>> + if (holeoff<= start)
>> + offset = start;
>> + else
>> + offset = min_t(loff_t, holeoff, isize);
>> +
>> + if (offset != file->f_pos)
>> + file->f_pos = offset;
>> +
>> +out_unlock:
>> + xfs_iunlock_map_shared(ip, lock);
>> +
>> + if (error)
>> + return -error;
>> + return offset;
>> +}
>
> Sorry this got set aside. This is being dusted off for inclusion.

Thanks for picking this up!

>
> Refresh my memory, do we need a XFS_FORCED_SHUTDOWN test in
> xfs_seek_hole()? In the earlier versions it was covered in the
> xfs_bmapi_read().

Yes, definitely.

>
> A comment on the min_t() that the xfs_bmap_first_unused() could
> return a value bigger than the isize if there are no more holes
> may help the forgetful such as myself.

I'll leave a comment for it, it would be helpful to recall the case for
a long period.

Thanks,
-Jeff

>
> Otherwise it looks good.
>
> Thank-you.
>
> Mark Tinguely <tinguely@sgi.com>
>
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