2016-10-29 08:14:13

by Ming Lei

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

Signed-off-by: Ming Lei <[email protected]>
---
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

2016-10-31 15:35:34

by Christoph Hellwig

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

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 <[email protected]>
> ---
> 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 [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
---end quoted text---

2016-10-31 23:12:36

by Ming Lei

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

On Mon, Oct 31, 2016 at 11:35 PM, Christoph Hellwig <[email protected]> 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 <[email protected]>
>> ---
>> 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 [email protected]
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
> ---end quoted text---


thanks,
Ming Lei