Re: [PATCH] io_uring/rsrc: ensure segments counts are correct on kbuf buffers

[Nitesh Shetty <nj.shetty@samsung.com>]

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On 17/04/25 06:29AM, Jens Axboe wrote:
>kbuf imports have the front offset adjusted and segments removed, but
>the tail segments are still included in the segment count that gets
>passed in the iov_iter. As the segments aren't necessarily all the
>same size, move importing to a separate helper and iterate the
>mapped length to get an exact count.
>
>Signed-off-by: Jens Axboe <axboe@kernel.dk>
>
>---
>
>Same as the one I sent out yesterday, but just for the kbuf part.
>
>diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
>index 4099b8225670..04e19689d2f3 100644
>--- a/io_uring/rsrc.c
>+++ b/io_uring/rsrc.c
>@@ -1032,6 +1032,26 @@ static int validate_fixed_range(u64 buf_addr, size_t len,
> 	return 0;
> }
>
>+static int io_import_kbuf(int ddir, struct iov_iter *iter,
>+			  struct io_mapped_ubuf *imu, size_t len, size_t offset)
>+{
>+	size_t count = len + offset;
>+
>+	iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, count);
>+	iov_iter_advance(iter, offset);
>+
>+	if (count < imu->len) {
>+		const struct bio_vec *bvec = iter->bvec;
>+
>+		while (len > bvec->bv_len) {
>+			len -= bvec->bv_len;
>+			bvec++;
>+		}
>+		iter->nr_segs = 1 + bvec - iter->bvec;
>+	}
>+	return 0;
>+}
>+
> static int io_import_fixed(int ddir, struct iov_iter *iter,
> 			   struct io_mapped_ubuf *imu,
> 			   u64 buf_addr, size_t len)
>@@ -1052,11 +1072,8 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
>
> 	offset = buf_addr - imu->ubuf;
>
>-	if (imu->is_kbuf) {
>-		iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, offset + len);
>-		iov_iter_advance(iter, offset);
>-		return 0;
>-	}
>+	if (imu->is_kbuf)
>+		return io_import_kbuf(ddir, iter, imu, len, offset);
>
> 	/*
> 	 * Don't use iov_iter_advance() here, as it's really slow for
>
Looks good.

Reviewed-by: Nitesh Shetty <nj.shetty@samsung.com>

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