[V11,07/19] fs/buffer.c: use bvec iterator to truncate the bio

Commit Message

Ming Lei Nov. 21, 2018, 3:23 a.m. UTC

Once multi-page bvec is enabled, the last bvec may include more than one
page, this patch use bvec_last_segment() to truncate the bio.

Reviewed-by: Omar Sandoval <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Ming Lei <[e-mail]>
---
 fs/buffer.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Christoph Hellwig Nov. 22, 2018, 10:58 a.m. UTC | #1

Btw, given that this is the last user of bvec_last_segment after my
other patches I think we should kill bvec_last_segment and do something
like this here:


diff --git a/fs/buffer.c b/fs/buffer.c
index fa37ad52e962..af5e135d2b83 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2981,6 +2981,14 @@ static void end_bio_bh_io_sync(struct bio *bio)
 	bio_put(bio);
 }
 
+static void zero_trailing_sectors(struct bio_vec *bvec, unsigned bytes)
+{
+	unsigned last_page = (bvec->bv_offset + bvec->bv_len - 1) >> PAGE_SHIFT;
+
+	zero_user(nth_page(bvec->bv_page, last_page),
+		  bvec->bv_offset % PAGE_SIZE + bvec->bv_len, bytes);
+}
+
 /*
  * This allows us to do IO even on the odd last sectors
  * of a device, even if the block size is some multiple
@@ -3031,13 +3039,8 @@ void guard_bio_eod(int op, struct bio *bio)
 	bvec->bv_len -= truncated_bytes;
 
 	/* ..and clear the end of the buffer for reads */
-	if (op == REQ_OP_READ) {
-		struct bio_vec bv;
-
-		bvec_last_segment(bvec, &bv);
-		zero_user(bv.bv_page, bv.bv_offset + bv.bv_len,
-				truncated_bytes);
-	}
+	if (op == REQ_OP_READ)
+		zero_trailing_sectors(bvec, truncated_bytes);
 }
 
 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,

Ming Lei Nov. 23, 2018, 1:48 a.m. UTC | #2

On Thu, Nov 22, 2018 at 11:58:49AM +0100, Christoph Hellwig wrote:
> Btw, given that this is the last user of bvec_last_segment after my
> other patches I think we should kill bvec_last_segment and do something
> like this here:
> 
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index fa37ad52e962..af5e135d2b83 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2981,6 +2981,14 @@ static void end_bio_bh_io_sync(struct bio *bio)
>  	bio_put(bio);
>  }
>  
> +static void zero_trailing_sectors(struct bio_vec *bvec, unsigned bytes)
> +{
> +	unsigned last_page = (bvec->bv_offset + bvec->bv_len - 1) >> PAGE_SHIFT;
> +
> +	zero_user(nth_page(bvec->bv_page, last_page),
> +		  bvec->bv_offset % PAGE_SIZE + bvec->bv_len, bytes);
> +}

The above 'start' parameter is figured out as wrong, and the computation
isn't very obvious, so I'd suggest to keep bvec_last_segment().

Thanks,
Ming

Patch

diff --git a/fs/buffer.c b/fs/buffer.c
index 1286c2b95498..fa37ad52e962 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3032,7 +3032,10 @@  void guard_bio_eod(int op, struct bio *bio)
 
 	/* ..and clear the end of the buffer for reads */
 	if (op == REQ_OP_READ) {
-		zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
+		struct bio_vec bv;
+
+		bvec_last_segment(bvec, &bv);
+		zero_user(bv.bv_page, bv.bv_offset + bv.bv_len,
 				truncated_bytes);
 	}
 }