[PATCH 0/2] fix/extend zone-append in block-layer

[PATCH 0/2] fix/extend zone-append in block-layer

[Kanchan Joshi]

First patch is about returning failure (rather than success) when
max_append_sectors is 0. This prevents bio_iov_iter_get_pages() from
getting into an endless loop.

Second patch enables issuing zone-append with iov_iter of bvec type.
It adds a helper which is similar to __bio_iov_bvec_add_pages() but
takes zone-append limits into account.

Kanchan Joshi (2):
  block: fix error code for zone-append
  block: enable zone-append for iov_iter of bvec type

 block/bio.c | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

-- 
2.7.4

[PATCH 1/2] block: fix error code for zone-append

[Kanchan Joshi]

avoid returning success when it should report failure, preventing
odd behavior in caller.

Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
---
 block/bio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index a7366c0..0cecdbc 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1044,7 +1044,7 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
 	size_t offset;
 
 	if (WARN_ON_ONCE(!max_append_sectors))
-		return 0;
+		return -EINVAL;
 
 	/*
 	 * Move page array up in the allocated memory for the bio vecs as far as
-- 
2.7.4

[PATCH 2/2] block: enable zone-append for iov_iter of bvec type

[Kanchan Joshi]

zone-append with bvec iov_iter gives WARN_ON, and returns -EINVAL.
Add new helper to process such iov_iter and add pages in bio honoring
zone-append specific constraints.

Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
---
 block/bio.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 0cecdbc..ade9da7 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -975,6 +975,30 @@ static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
 	iov_iter_advance(iter, size);
 	return 0;
 }
+static int __bio_iov_bvec_append_add_pages(struct bio *bio, struct iov_iter *iter)
+{
+	const struct bio_vec *bv = iter->bvec;
+	unsigned int len;
+	size_t size;
+	struct request_queue *q = bio->bi_disk->queue;
+	unsigned int max_append_sectors = queue_max_zone_append_sectors(q);
+	bool same_page = false;
+
+	if (WARN_ON_ONCE(!max_append_sectors))
+		return -EINVAL;
+
+	if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len))
+		return -EINVAL;
+
+	len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count);
+	size = bio_add_hw_page(q, bio, bv->bv_page, len,
+				bv->bv_offset + iter->iov_offset,
+				max_append_sectors, &same_page);
+	if (unlikely(size != len))
+		return -EINVAL;
+	iov_iter_advance(iter, size);
+	return 0;
+}
 
 #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))
 
@@ -1105,9 +1129,10 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 
 	do {
 		if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
-			if (WARN_ON_ONCE(is_bvec))
-				return -EINVAL;
-			ret = __bio_iov_append_get_pages(bio, iter);
+			if (is_bvec)
+				ret = __bio_iov_bvec_append_add_pages(bio, iter);
+			else
+				ret = __bio_iov_append_get_pages(bio, iter);
 		} else {
 			if (is_bvec)
 				ret = __bio_iov_bvec_add_pages(bio, iter);
-- 
2.7.4

Re: [PATCH 1/2] block: fix error code for zone-append

[Damien Le Moal]

On 2020/07/03 0:42, Kanchan Joshi wrote:
> avoid returning success when it should report failure, preventing
> odd behavior in caller.

You can be more precise here: the odd behavior is an infinite loop in
bio_iov_iter_get_pages() whcih is is the only user of __bio_iov_append_get_pages().

> 
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
> ---
>  block/bio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index a7366c0..0cecdbc 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1044,7 +1044,7 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
>  	size_t offset;
>  
>  	if (WARN_ON_ONCE(!max_append_sectors))
> -		return 0;
> +		return -EINVAL;
>  
>  	/*
>  	 * Move page array up in the allocated memory for the bio vecs as far as
> 

Note: the odd behavior mentioned in the commit message cannot currently be
triggered since only zonefs issues REQ_OP_ZONE_APPEND BIOs so we are guaranteed
that max_append_sectors is not 0 in that case. But this fix certainly makes
things more solid. So:

Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>

-- 
Damien Le Moal
Western Digital Research

Re: [PATCH 2/2] block: enable zone-append for iov_iter of bvec type

[Damien Le Moal]

On 2020/07/03 0:42, Kanchan Joshi wrote:
> zone-append with bvec iov_iter gives WARN_ON, and returns -EINVAL.
> Add new helper to process such iov_iter and add pages in bio honoring
> zone-append specific constraints.
> 
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
> ---
>  block/bio.c | 31 ++++++++++++++++++++++++++++---
>  1 file changed, 28 insertions(+), 3 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 0cecdbc..ade9da7 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -975,6 +975,30 @@ static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
>  	iov_iter_advance(iter, size);
>  	return 0;
>  }
> +static int __bio_iov_bvec_append_add_pages(struct bio *bio, struct iov_iter *iter)
> +{
> +	const struct bio_vec *bv = iter->bvec;
> +	unsigned int len;
> +	size_t size;
> +	struct request_queue *q = bio->bi_disk->queue;
> +	unsigned int max_append_sectors = queue_max_zone_append_sectors(q);
> +	bool same_page = false;
> +
> +	if (WARN_ON_ONCE(!max_append_sectors))
> +		return -EINVAL;
> +
> +	if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len))
> +		return -EINVAL;
> +
> +	len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count);
> +	size = bio_add_hw_page(q, bio, bv->bv_page, len,
> +				bv->bv_offset + iter->iov_offset,
> +				max_append_sectors, &same_page);
> +	if (unlikely(size != len))
> +		return -EINVAL;
> +	iov_iter_advance(iter, size);
> +	return 0;
> +}
>  
>  #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))
>  
> @@ -1105,9 +1129,10 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  
>  	do {
>  		if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
> -			if (WARN_ON_ONCE(is_bvec))
> -				return -EINVAL;
> -			ret = __bio_iov_append_get_pages(bio, iter);
> +			if (is_bvec)
> +				ret = __bio_iov_bvec_append_add_pages(bio, iter);
> +			else
> +				ret = __bio_iov_append_get_pages(bio, iter);
>  		} else {
>  			if (is_bvec)
>  				ret = __bio_iov_bvec_add_pages(bio, iter);
> 

The only user of this function that issues zone append requests is zonefs. The
issued requests are not using bvec iter but a user direct IO buffer iter. So
this change would have no user at all as far as I can see. Am I missing
something ? What IO path makes this change necessary ?


-- 
Damien Le Moal
Western Digital Research

Re: [PATCH 1/2] block: fix error code for zone-append

[Kanchan Joshi]

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On Fri, Jul 03, 2020 at 05:29:50AM +0000, Damien Le Moal wrote:
>On 2020/07/03 0:42, Kanchan Joshi wrote:
>> avoid returning success when it should report failure, preventing
>> odd behavior in caller.
>
>You can be more precise here: the odd behavior is an infinite loop in
>bio_iov_iter_get_pages() whcih is is the only user of __bio_iov_append_get_pages().
Sure. Kept that in cover letter, but missed here.
>>
>> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
>> Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>> ---
>>  block/bio.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/block/bio.c b/block/bio.c
>> index a7366c0..0cecdbc 100644
>> --- a/block/bio.c
>> +++ b/block/bio.c
>> @@ -1044,7 +1044,7 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
>>  	size_t offset;
>>
>>  	if (WARN_ON_ONCE(!max_append_sectors))
>> -		return 0;
>> +		return -EINVAL;
>>
>>  	/*
>>  	 * Move page array up in the allocated memory for the bio vecs as far as
>>
>
>Note: the odd behavior mentioned in the commit message cannot currently be
>triggered since only zonefs issues REQ_OP_ZONE_APPEND BIOs so we are guaranteed
>that max_append_sectors is not 0 in that case. But this fix certainly makes
>things more solid. So:
Yes, zonefs will not run into this. Future users of zone-append may. I
encountered this endless loop while testing user zone-append path.
>Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
>
>-- 
>Damien Le Moal
>Western Digital Research
>

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Re: [PATCH 2/2] block: enable zone-append for iov_iter of bvec type

[Kanchan Joshi]

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On Fri, Jul 03, 2020 at 05:32:56AM +0000, Damien Le Moal wrote:
>On 2020/07/03 0:42, Kanchan Joshi wrote:
>> zone-append with bvec iov_iter gives WARN_ON, and returns -EINVAL.
>> Add new helper to process such iov_iter and add pages in bio honoring
>> zone-append specific constraints.
>>
>> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
>> Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>> ---
>>  block/bio.c | 31 ++++++++++++++++++++++++++++---
>>  1 file changed, 28 insertions(+), 3 deletions(-)
>>
>> diff --git a/block/bio.c b/block/bio.c
>> index 0cecdbc..ade9da7 100644
>> --- a/block/bio.c
>> +++ b/block/bio.c
>> @@ -975,6 +975,30 @@ static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
>>  	iov_iter_advance(iter, size);
>>  	return 0;
>>  }
>> +static int __bio_iov_bvec_append_add_pages(struct bio *bio, struct iov_iter *iter)
>> +{
>> +	const struct bio_vec *bv = iter->bvec;
>> +	unsigned int len;
>> +	size_t size;
>> +	struct request_queue *q = bio->bi_disk->queue;
>> +	unsigned int max_append_sectors = queue_max_zone_append_sectors(q);
>> +	bool same_page = false;
>> +
>> +	if (WARN_ON_ONCE(!max_append_sectors))
>> +		return -EINVAL;
>> +
>> +	if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len))
>> +		return -EINVAL;
>> +
>> +	len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count);
>> +	size = bio_add_hw_page(q, bio, bv->bv_page, len,
>> +				bv->bv_offset + iter->iov_offset,
>> +				max_append_sectors, &same_page);
>> +	if (unlikely(size != len))
>> +		return -EINVAL;
>> +	iov_iter_advance(iter, size);
>> +	return 0;
>> +}
>>
>>  #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))
>>
>> @@ -1105,9 +1129,10 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>>
>>  	do {
>>  		if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
>> -			if (WARN_ON_ONCE(is_bvec))
>> -				return -EINVAL;
>> -			ret = __bio_iov_append_get_pages(bio, iter);
>> +			if (is_bvec)
>> +				ret = __bio_iov_bvec_append_add_pages(bio, iter);
>> +			else
>> +				ret = __bio_iov_append_get_pages(bio, iter);
>>  		} else {
>>  			if (is_bvec)
>>  				ret = __bio_iov_bvec_add_pages(bio, iter);
>>
>
>The only user of this function that issues zone append requests is zonefs. The
>issued requests are not using bvec iter but a user direct IO buffer iter. So
>this change would have no user at all as far as I can see. Am I missing
>something ? What IO path makes this change necessary ?

Yes, zonefs does not use bvec iter. But while enabling io-uring path for
zone-append, I hit into this condition returning -EINVAL. 

Reference (from user zone-append series cover letter):
"Append using io_uring fixed-buffer --->
This is flagged as not-supported at the moment. Reason being, for fixed-buffer
io-uring sends iov_iter of bvec type. But current append-infra in block-layer
does not support such iov_iter."

And zone-append doesn't have a problem in using bvec iter as well, so
thought that this may make infra more complete/future-proof?

>-- 
>Damien Le Moal
>Western Digital Research
>

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Re: [PATCH 2/2] block: enable zone-append for iov_iter of bvec type

[Damien Le Moal]

On 2020/07/03 15:56, Kanchan Joshi wrote:
> On Fri, Jul 03, 2020 at 05:32:56AM +0000, Damien Le Moal wrote:
>> On 2020/07/03 0:42, Kanchan Joshi wrote:
>>> zone-append with bvec iov_iter gives WARN_ON, and returns -EINVAL.
>>> Add new helper to process such iov_iter and add pages in bio honoring
>>> zone-append specific constraints.
>>>
>>> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
>>> Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
>>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>>> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
>>> ---
>>>  block/bio.c | 31 ++++++++++++++++++++++++++++---
>>>  1 file changed, 28 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/block/bio.c b/block/bio.c
>>> index 0cecdbc..ade9da7 100644
>>> --- a/block/bio.c
>>> +++ b/block/bio.c
>>> @@ -975,6 +975,30 @@ static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
>>>  	iov_iter_advance(iter, size);
>>>  	return 0;
>>>  }
>>> +static int __bio_iov_bvec_append_add_pages(struct bio *bio, struct iov_iter *iter)
>>> +{
>>> +	const struct bio_vec *bv = iter->bvec;
>>> +	unsigned int len;
>>> +	size_t size;
>>> +	struct request_queue *q = bio->bi_disk->queue;
>>> +	unsigned int max_append_sectors = queue_max_zone_append_sectors(q);
>>> +	bool same_page = false;
>>> +
>>> +	if (WARN_ON_ONCE(!max_append_sectors))
>>> +		return -EINVAL;
>>> +
>>> +	if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len))
>>> +		return -EINVAL;
>>> +
>>> +	len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count);
>>> +	size = bio_add_hw_page(q, bio, bv->bv_page, len,
>>> +				bv->bv_offset + iter->iov_offset,
>>> +				max_append_sectors, &same_page);
>>> +	if (unlikely(size != len))
>>> +		return -EINVAL;
>>> +	iov_iter_advance(iter, size);
>>> +	return 0;
>>> +}
>>>
>>>  #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))
>>>
>>> @@ -1105,9 +1129,10 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>>>
>>>  	do {
>>>  		if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
>>> -			if (WARN_ON_ONCE(is_bvec))
>>> -				return -EINVAL;
>>> -			ret = __bio_iov_append_get_pages(bio, iter);
>>> +			if (is_bvec)
>>> +				ret = __bio_iov_bvec_append_add_pages(bio, iter);
>>> +			else
>>> +				ret = __bio_iov_append_get_pages(bio, iter);
>>>  		} else {
>>>  			if (is_bvec)
>>>  				ret = __bio_iov_bvec_add_pages(bio, iter);
>>>
>>
>> The only user of this function that issues zone append requests is zonefs. The
>> issued requests are not using bvec iter but a user direct IO buffer iter. So
>> this change would have no user at all as far as I can see. Am I missing
>> something ? What IO path makes this change necessary ?
> 
> Yes, zonefs does not use bvec iter. But while enabling io-uring path for
> zone-append, I hit into this condition returning -EINVAL. 
> 
> Reference (from user zone-append series cover letter):
> "Append using io_uring fixed-buffer --->
> This is flagged as not-supported at the moment. Reason being, for fixed-buffer
> io-uring sends iov_iter of bvec type. But current append-infra in block-layer
> does not support such iov_iter."
> 
> And zone-append doesn't have a problem in using bvec iter as well, so
> thought that this may make infra more complete/future-proof?

As long as there is no possible user for this change, I do not see the point in
adding it.


-- 
Damien Le Moal
Western Digital Research

Re: [PATCH 2/2] block: enable zone-append for iov_iter of bvec type

[Johannes Thumshirn]

On 03/07/2020 08:56, Kanchan Joshi wrote:
[...]
> Yes, zonefs does not use bvec iter. But while enabling io-uring path for
> zone-append, I hit into this condition returning -EINVAL. 
> 
> Reference (from user zone-append series cover letter):
> "Append using io_uring fixed-buffer --->
> This is flagged as not-supported at the moment. Reason being, for fixed-buffer
> io-uring sends iov_iter of bvec type. But current append-infra in block-layer
> does not support such iov_iter."
> 
> And zone-append doesn't have a problem in using bvec iter as well, so
> thought that this may make infra more complete/future-proof?

As long as it's no problem for current in-tree users please keep it as is. 
Please submit this patch together with your io_uring series as a preparatory patch.