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Thu, 26 Mar 2026 06:48:11 -0400 X-MC-Unique: H2PjY8ChMyuS7rT40AhezQ-1 X-Mimecast-MFC-AGG-ID: H2PjY8ChMyuS7rT40AhezQ_1774522089 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E6D89180034E; Thu, 26 Mar 2026 10:48:08 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.44.33.121]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 783F11955F25; Thu, 26 Mar 2026 10:48:02 +0000 (UTC) From: David Howells To: Christian Brauner , Matthew Wilcox , Christoph Hellwig Cc: David Howells , Paulo Alcantara , Jens Axboe , Leon Romanovsky , Steve French , ChenXiaoSong , Marc Dionne , Eric Van Hensbergen , Dominique Martinet , Ilya Dryomov , Trond Myklebust , netfs@lists.linux.dev, linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs@lists.linux.dev, linux-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Paulo Alcantara Subject: [PATCH 14/26] netfs: Add a function to extract from an iter into a bvecq Date: Thu, 26 Mar 2026 10:45:29 +0000 Message-ID: <20260326104544.509518-15-dhowells@redhat.com> In-Reply-To: <20260326104544.509518-1-dhowells@redhat.com> References: <20260326104544.509518-1-dhowells@redhat.com> X-Mailing-List: linux-erofs@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-MFC-PROC-ID: 1Z7gTNK2UaWslVmlZeyki429ZCkBGjuG-kKklPu6mN0_1774522089 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true Add a function to extract a slice of data from an iterator of any type into a bvec queue chain. Signed-off-by: David Howells cc: Paulo Alcantara cc: Matthew Wilcox cc: Christoph Hellwig cc: Steve French cc: linux-cifs@vger.kernel.org cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org --- fs/netfs/iterator.c | 123 ++++++++++++++++++++++++++++++++++++++++++ include/linux/netfs.h | 3 ++ 2 files changed, 126 insertions(+) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index adca78747f23..e77fd39327c2 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -13,6 +13,129 @@ #include #include "internal.h" +/** + * netfs_extract_iter - Extract the pages from an iterator into a bvecq + * @orig: The original iterator + * @orig_len: The amount of iterator to copy + * @max_segs: Maximum number of contiguous segments + * @fpos: Starting file position to label the bvecq with + * @_bvecq_head: Where to cache the bvec queue + * @extraction_flags: Flags to qualify the request + * + * Extract the page fragments from the given amount of the source iterator and + * build bvec queue that refers to all of those bits. This allows the original + * iterator to disposed of. + * + * @extraction_flags can have ITER_ALLOW_P2PDMA set to request peer-to-peer DMA be + * allowed on the pages extracted. + * + * On success, the amount of data in the bvec is returned, the original + * iterator will have been advanced by the amount extracted. + * + * The bvecq segments are marked with indications on how to get clean up the + * extracted fragments. + */ +ssize_t netfs_extract_iter(struct iov_iter *orig, size_t orig_len, size_t max_segs, + unsigned long long fpos, struct bvecq **_bvecq_head, + iov_iter_extraction_t extraction_flags) +{ + struct bvecq *bq_tail = NULL; + ssize_t ret = 0; + size_t extracted = 0, nr_pages; + + _enter("{%u,%zx},%zx", orig->iter_type, orig->count, orig_len); + + WARN_ON_ONCE(orig_len > orig->count); + + nr_pages = iov_iter_npages(orig, max_segs ?: INT_MAX); + if (WARN_ON(nr_pages == 0) || + WARN_ON(nr_pages > max_segs)) + nr_pages = max_segs; + max_segs = nr_pages; + + do { + struct bvecq *bq; + + if (WARN_ON(max_segs == 0)) + break; + + bq = bvecq_alloc_one(max_segs, GFP_NOFS); + if (!bq) { + ret = -ENOMEM; + break; + } + bq->free = user_backed_iter(orig); + bq->unpin = iov_iter_extract_will_pin(orig); + bq->prev = bq_tail; + bq->fpos = fpos + extracted; + + if (bq_tail) + bq_tail->next = bq; + else + *_bvecq_head = bq; + bq_tail = bq; + + if (orig_len == 0) + break; + + struct bio_vec *bv = bq->bv; + do { + struct page **pages; + ssize_t got; + size_t offset; + size_t space = bq->max_slots - bq->nr_slots; + size_t bv_size = array_size(bq->max_slots, sizeof(*bv)); + size_t pg_size = array_size(space, sizeof(*pages)); + + /* Put the page list at the end of the bvec list + * storage. bvec elements are larger than page + * pointers, so as long as we work 0->last, we should + * be fine. + */ + pages = (void *)bv + bv_size - pg_size; + + got = iov_iter_extract_pages(orig, &pages, orig_len, + space, extraction_flags, &offset); + if (got < 0) { + ret = got; + goto out; + } + + if (got == 0) { + pr_err("extract_pages gave nothing from %zu, %zu\n", + extracted, orig_len); + ret = -EIO; + goto out; + } + + if (got > orig_len - extracted) { + pr_err("extract_pages rc=%zd more than %zu\n", + got, orig_len); + goto out; + } + + extracted += got; + orig_len -= got; + + do { + size_t len = umin(got, PAGE_SIZE - offset); + + BUG_ON(bq->nr_slots >= bq->max_slots); + + bvec_set_page(&bq->bv[bq->nr_slots], + *pages++, len, offset); + bq->nr_slots++; + got -= len; + offset = 0; + } while (got > 0); + } while (orig_len > 0 && !bvecq_is_full(bq)); + } while (orig_len > 0 && max_segs > 0); + +out: + return extracted ?: ret; +} +EXPORT_SYMBOL_GPL(netfs_extract_iter); + /** * netfs_extract_user_iter - Extract the pages from a user iterator into a bvec * @orig: The original iterator diff --git a/include/linux/netfs.h b/include/linux/netfs.h index 5bc48aacf7f6..b4602f7b6431 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -445,6 +445,9 @@ void netfs_get_subrequest(struct netfs_io_subrequest *subreq, enum netfs_sreq_ref_trace what); void netfs_put_subrequest(struct netfs_io_subrequest *subreq, enum netfs_sreq_ref_trace what); +ssize_t netfs_extract_iter(struct iov_iter *orig, size_t orig_len, size_t max_segs, + unsigned long long fpos, struct bvecq **_bvecq_head, + iov_iter_extraction_t extraction_flags); ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len, struct iov_iter *new, iov_iter_extraction_t extraction_flags);