[PATCH] xfs: Make fiemap works with sparse file.

[PATCH] xfs: Make fiemap works with sparse file.

[Tao Ma]

In xfs_vn_fiemap, we set bvm_count to fi_extent_max + 1 and want
to return fi_extent_max extents, but actually it won't work for
a sparse file. The reason is that in xfs_getbmap we will
calculate holes and set it in 'out', while out is malloced by
bmv_count(fi_extent_max+1) which didn't consider holes. So in the
worst case, if 'out' vector looks like
[hole, extent, hole, extent, hole, ... hole, extent, hole],
we will only return half of fi_extent_max extents.

So in xfs_vn_fiemap, we should consider this worst case. If the
user wants fi_extent_max extents, we need a 'out' with size of
2 *fi_extent_max + 1.

Cc: Alex Elder <aelder@sgi.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Tao Ma <tao.ma@oracle.com>
---
 fs/xfs/linux-2.6/xfs_iops.c |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c
index 9c8019c..1db92e3 100644
--- a/fs/xfs/linux-2.6/xfs_iops.c
+++ b/fs/xfs/linux-2.6/xfs_iops.c
@@ -672,9 +672,21 @@ xfs_vn_fiemap(
 	else
 		bm.bmv_length = BTOBB(length);
 
-	/* We add one because in getbmap world count includes the header */
+	/*
+	 * It is a bit tricky for us to calculate the bmv_count from
+	 * fi_extent_max.
+	 * If we support to return fi_extent_max extents to the user,
+	 * we need at most 2 * fi_extent_max + 1 for bmv_count since
+	 * in xfs_getbmap we will calculate holes while fi_extent_max
+	 * don't have them. So in the worst case, bmv can looks like
+	 * [hole, extent, hole, extent, hole, ... hole, extent, hole].
+	 * So there will be 2 *fi_extent_max + 1.
+	 * What's more, in getbmap world count have to include the
+	 * header, so we need another bmv. So the total number will
+	 * be 2 * fieinfo->fi_extents_max + 2.
+	 */
 	bm.bmv_count = !fieinfo->fi_extents_max ? MAXEXTNUM :
-					fieinfo->fi_extents_max + 1;
+			2 * fieinfo->fi_extents_max + 2;
 	bm.bmv_count = min_t(__s32, bm.bmv_count,
 			     (PAGE_SIZE * 16 / sizeof(struct getbmapx)));
 	bm.bmv_iflags = BMV_IF_PREALLOC;
-- 
1.5.5

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Re: [PATCH] xfs: Make fiemap works with sparse file.

[Eric Sandeen]

Tao Ma wrote:
> In xfs_vn_fiemap, we set bvm_count to fi_extent_max + 1 and want
> to return fi_extent_max extents, but actually it won't work for
> a sparse file. The reason is that in xfs_getbmap we will
> calculate holes and set it in 'out', while out is malloced by
> bmv_count(fi_extent_max+1) which didn't consider holes. So in the
> worst case, if 'out' vector looks like
> [hole, extent, hole, extent, hole, ... hole, extent, hole],
> we will only return half of fi_extent_max extents.
> 
> So in xfs_vn_fiemap, we should consider this worst case. If the
> user wants fi_extent_max extents, we need a 'out' with size of
> 2 *fi_extent_max + 1.

This all seems right to me, though your commit message above (+1)
doesn't match the comment and code in the patch (+2)

-Eric

> Cc: Alex Elder <aelder@sgi.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Dave Chinner <david@fromorbit.com>
> Signed-off-by: Tao Ma <tao.ma@oracle.com>
> ---
>  fs/xfs/linux-2.6/xfs_iops.c |   16 ++++++++++++++--
>  1 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c
> index 9c8019c..1db92e3 100644
> --- a/fs/xfs/linux-2.6/xfs_iops.c
> +++ b/fs/xfs/linux-2.6/xfs_iops.c
> @@ -672,9 +672,21 @@ xfs_vn_fiemap(
>  	else
>  		bm.bmv_length = BTOBB(length);
>  
> -	/* We add one because in getbmap world count includes the header */
> +	/*
> +	 * It is a bit tricky for us to calculate the bmv_count from
> +	 * fi_extent_max.
> +	 * If we support to return fi_extent_max extents to the user,
> +	 * we need at most 2 * fi_extent_max + 1 for bmv_count since
> +	 * in xfs_getbmap we will calculate holes while fi_extent_max
> +	 * don't have them. So in the worst case, bmv can looks like
> +	 * [hole, extent, hole, extent, hole, ... hole, extent, hole].
> +	 * So there will be 2 *fi_extent_max + 1.
> +	 * What's more, in getbmap world count have to include the
> +	 * header, so we need another bmv. So the total number will
> +	 * be 2 * fieinfo->fi_extents_max + 2.
> +	 */
>  	bm.bmv_count = !fieinfo->fi_extents_max ? MAXEXTNUM :
> -					fieinfo->fi_extents_max + 1;
> +			2 * fieinfo->fi_extents_max + 2;
>  	bm.bmv_count = min_t(__s32, bm.bmv_count,
>  			     (PAGE_SIZE * 16 / sizeof(struct getbmapx)));
>  	bm.bmv_iflags = BMV_IF_PREALLOC;

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Re: [PATCH] xfs: Make fiemap works with sparse file.

[Tao Ma]

Eric Sandeen wrote:
> Tao Ma wrote:
>   
>> In xfs_vn_fiemap, we set bvm_count to fi_extent_max + 1 and want
>> to return fi_extent_max extents, but actually it won't work for
>> a sparse file. The reason is that in xfs_getbmap we will
>> calculate holes and set it in 'out', while out is malloced by
>> bmv_count(fi_extent_max+1) which didn't consider holes. So in the
>> worst case, if 'out' vector looks like
>> [hole, extent, hole, extent, hole, ... hole, extent, hole],
>> we will only return half of fi_extent_max extents.
>>
>> So in xfs_vn_fiemap, we should consider this worst case. If the
>> user wants fi_extent_max extents, we need a 'out' with size of
>> 2 *fi_extent_max + 1.
>>     
>
> This all seems right to me, though your commit message above (+1)
> doesn't match the comment and code in the patch (+2)
>   
oh, yes, I will change the commit log and send a v2.
and can I add your ack for this patch?

Regards,
Tao
> -Eric
>
>   
>> Cc: Alex Elder <aelder@sgi.com>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Dave Chinner <david@fromorbit.com>
>> Signed-off-by: Tao Ma <tao.ma@oracle.com>
>> ---
>>  fs/xfs/linux-2.6/xfs_iops.c |   16 ++++++++++++++--
>>  1 files changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c
>> index 9c8019c..1db92e3 100644
>> --- a/fs/xfs/linux-2.6/xfs_iops.c
>> +++ b/fs/xfs/linux-2.6/xfs_iops.c
>> @@ -672,9 +672,21 @@ xfs_vn_fiemap(
>>  	else
>>  		bm.bmv_length = BTOBB(length);
>>  
>> -	/* We add one because in getbmap world count includes the header */
>> +	/*
>> +	 * It is a bit tricky for us to calculate the bmv_count from
>> +	 * fi_extent_max.
>> +	 * If we support to return fi_extent_max extents to the user,
>> +	 * we need at most 2 * fi_extent_max + 1 for bmv_count since
>> +	 * in xfs_getbmap we will calculate holes while fi_extent_max
>> +	 * don't have them. So in the worst case, bmv can looks like
>> +	 * [hole, extent, hole, extent, hole, ... hole, extent, hole].
>> +	 * So there will be 2 *fi_extent_max + 1.
>> +	 * What's more, in getbmap world count have to include the
>> +	 * header, so we need another bmv. So the total number will
>> +	 * be 2 * fieinfo->fi_extents_max + 2.
>> +	 */
>>  	bm.bmv_count = !fieinfo->fi_extents_max ? MAXEXTNUM :
>> -					fieinfo->fi_extents_max + 1;
>> +			2 * fieinfo->fi_extents_max + 2;
>>  	bm.bmv_count = min_t(__s32, bm.bmv_count,
>>  			     (PAGE_SIZE * 16 / sizeof(struct getbmapx)));
>>  	bm.bmv_iflags = BMV_IF_PREALLOC;
>>     
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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>   

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Re: [PATCH] xfs: Make fiemap works with sparse file.

[Eric Sandeen]

Tao Ma wrote:
> Eric Sandeen wrote:
>> Tao Ma wrote:
>>  
>>> In xfs_vn_fiemap, we set bvm_count to fi_extent_max + 1 and want
>>> to return fi_extent_max extents, but actually it won't work for
>>> a sparse file. The reason is that in xfs_getbmap we will
>>> calculate holes and set it in 'out', while out is malloced by
>>> bmv_count(fi_extent_max+1) which didn't consider holes. So in the
>>> worst case, if 'out' vector looks like
>>> [hole, extent, hole, extent, hole, ... hole, extent, hole],
>>> we will only return half of fi_extent_max extents.
>>>
>>> So in xfs_vn_fiemap, we should consider this worst case. If the
>>> user wants fi_extent_max extents, we need a 'out' with size of
>>> 2 *fi_extent_max + 1.
>>>     
>>
>> This all seems right to me, though your commit message above (+1)
>> doesn't match the comment and code in the patch (+2)
>>   
> oh, yes, I will change the commit log and send a v2.
> and can I add your ack for this patch?

Sure, it seems right to me.

Thanks,
-Eric

> Regards,
> Tao
>> -Eric
>>
>>  
>>> Cc: Alex Elder <aelder@sgi.com>
>>> Cc: Christoph Hellwig <hch@lst.de>
>>> Cc: Dave Chinner <david@fromorbit.com>
>>> Signed-off-by: Tao Ma <tao.ma@oracle.com>
>>> ---
>>>  fs/xfs/linux-2.6/xfs_iops.c |   16 ++++++++++++++--
>>>  1 files changed, 14 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c
>>> index 9c8019c..1db92e3 100644
>>> --- a/fs/xfs/linux-2.6/xfs_iops.c
>>> +++ b/fs/xfs/linux-2.6/xfs_iops.c
>>> @@ -672,9 +672,21 @@ xfs_vn_fiemap(
>>>      else
>>>          bm.bmv_length = BTOBB(length);
>>>  
>>> -    /* We add one because in getbmap world count includes the header */
>>> +    /*
>>> +     * It is a bit tricky for us to calculate the bmv_count from
>>> +     * fi_extent_max.
>>> +     * If we support to return fi_extent_max extents to the user,
>>> +     * we need at most 2 * fi_extent_max + 1 for bmv_count since
>>> +     * in xfs_getbmap we will calculate holes while fi_extent_max
>>> +     * don't have them. So in the worst case, bmv can looks like
>>> +     * [hole, extent, hole, extent, hole, ... hole, extent, hole].
>>> +     * So there will be 2 *fi_extent_max + 1.
>>> +     * What's more, in getbmap world count have to include the
>>> +     * header, so we need another bmv. So the total number will
>>> +     * be 2 * fieinfo->fi_extents_max + 2.
>>> +     */
>>>      bm.bmv_count = !fieinfo->fi_extents_max ? MAXEXTNUM :
>>> -                    fieinfo->fi_extents_max + 1;
>>> +            2 * fieinfo->fi_extents_max + 2;
>>>      bm.bmv_count = min_t(__s32, bm.bmv_count,
>>>                   (PAGE_SIZE * 16 / sizeof(struct getbmapx)));
>>>      bm.bmv_iflags = BMV_IF_PREALLOC;
>>>     
>>
>> -- 
>> To unsubscribe from this list: send the line "unsubscribe
>> linux-kernel" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> Please read the FAQ at  http://www.tux.org/lkml/
>>   
> 

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