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

[Ming Lei]

On Mon, Oct 31, 2016 at 11:35 PM, Christoph Hellwig <hch@xxxxxxxxxxxxx> 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@xxxxxxxxx>
>> ---
>>  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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> ---end quoted text---


thanks,
Ming Lei