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[PATCH 19/60] fs/buffer: comment on direct access to bvec table

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  [PATCH 19/60] fs/buffer: comment on direct access to bvec table Ming Lei <tom.leiming@gmail.com> - 2016-10-29 10:30 +0200
    Re: [PATCH 19/60] fs/buffer: comment on direct access to bvec table Christoph Hellwig <hch@infradead.org> - 2016-10-31 16:40 +0100
      Re: [PATCH 19/60] fs/buffer: comment on direct access to bvec table Ming Lei <tom.leiming@gmail.com> - 2016-11-01 00:20 +0100

#1511580 — [PATCH 19/60] fs/buffer: comment on direct access to bvec table

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 fs/buffer.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index b205a629001d..81c3793948b4 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3018,8 +3018,13 @@ static void end_bio_bh_io_sync(struct bio *bio)
 void guard_bio_eod(int op, struct bio *bio)
 {
 	sector_t maxsector;
-	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
 	unsigned truncated_bytes;
+	/*
+	 * It is safe to truncate the last bvec in the following way
+	 * even though multipage bvec is supported, but we need to
+	 * fix the parameters passed to zero_user().
+	 */
+	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
 
 	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
 	if (!maxsector)
-- 
2.7.4

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#1512635

I think we'll just need a version zero_fill_bio with a length argument
and let that handle all the bvec access.  I have vague memories that
Kent posted one a while ago, Ccing him.

On Sat, Oct 29, 2016 at 04:08:18PM +0800, Ming Lei wrote:
> Signed-off-by: Ming Lei <tom.leiming@gmail.com>
> ---
>  fs/buffer.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index b205a629001d..81c3793948b4 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -3018,8 +3018,13 @@ static void end_bio_bh_io_sync(struct bio *bio)
>  void guard_bio_eod(int op, struct bio *bio)
>  {
>  	sector_t maxsector;
> -	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
>  	unsigned truncated_bytes;
> +	/*
> +	 * It is safe to truncate the last bvec in the following way
> +	 * even though multipage bvec is supported, but we need to
> +	 * fix the parameters passed to zero_user().
> +	 */
> +	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
>  
>  	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
>  	if (!maxsector)
> -- 
> 2.7.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-block" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
---end quoted text---

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#1512989

On Mon, Oct 31, 2016 at 11:35 PM, Christoph Hellwig <hch@infradead.org> wrote:
>
> I think we'll just need a version zero_fill_bio with a length argument
> and let that handle all the bvec access.  I have vague memories that
> Kent posted one a while ago, Ccing him.

I will try to find zero_fill_bio() in Kent's tree later.

BTW, patch 59 switches to use bvec iterator to do that too.

>
> On Sat, Oct 29, 2016 at 04:08:18PM +0800, Ming Lei wrote:
>> Signed-off-by: Ming Lei <tom.leiming@gmail.com>
>> ---
>>  fs/buffer.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/buffer.c b/fs/buffer.c
>> index b205a629001d..81c3793948b4 100644
>> --- a/fs/buffer.c
>> +++ b/fs/buffer.c
>> @@ -3018,8 +3018,13 @@ static void end_bio_bh_io_sync(struct bio *bio)
>>  void guard_bio_eod(int op, struct bio *bio)
>>  {
>>       sector_t maxsector;
>> -     struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
>>       unsigned truncated_bytes;
>> +     /*
>> +      * It is safe to truncate the last bvec in the following way
>> +      * even though multipage bvec is supported, but we need to
>> +      * fix the parameters passed to zero_user().
>> +      */
>> +     struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
>>
>>       maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
>>       if (!maxsector)
>> --
>> 2.7.4
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-block" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> ---end quoted text---


thanks,
Ming Lei

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