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 | 122 ++++++++++++++++++++++++++++++++++++++++++ include/linux/netfs.h | 3 ++ 2 files changed, 125 insertions(+) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index 72a435e5fc6d..faf4f0a3b33d 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -13,6 +13,128 @@ #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 segs_per_bq; + size_t extracted = 0; + + _enter("{%u,%zx},%zx", orig->iter_type, orig->count, orig_len); + + if (max_segs == 0) + max_segs = ULONG_MAX; + + /* We want the biggest pow-of-2 size that has at most 255 segs and that + * won't exceed a 4K page. + */ + segs_per_bq = (4096 - sizeof(*bq_tail)) / sizeof(bq_tail->__bv[0]); + if (segs_per_bq > 255) + segs_per_bq = (2048 - sizeof(*bq_tail)) / sizeof(bq_tail->__bv[0]); + + do { + struct bvecq *bq; + size_t nr_slots = iov_iter_npages(orig, umin(segs_per_bq, max_segs)); + + if (WARN_ON(nr_slots == 0 && extracted < orig_len) || + WARN_ON(nr_slots > max_segs)) + break; + max_segs -= nr_slots; + + bq = netfs_alloc_one_bvecq(nr_slots, 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 (extracted >= orig_len) + break; + + /* 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. + */ + struct bio_vec *bv = bq->bv; + struct page **pages; + size_t bv_size = array_size(bq->max_segs, sizeof(*bv)); + size_t pg_size = array_size(bq->max_segs, sizeof(*pages)); + + pages = (void *)bv + bv_size - pg_size; + + do { + unsigned int cur_npages; + ssize_t got; + size_t offset; + + got = iov_iter_extract_pages(orig, &pages, orig_len - extracted, + bq->max_segs - bq->nr_segs, + extraction_flags, &offset); + if (got < 0) { + pr_err("Couldn't get user pages (rc=%zd)\n", got); + ret = got; + break; + } + + if (got > orig_len - extracted) { + pr_err("get_pages rc=%zd more than %zu\n", + got, orig_len - extracted); + break; + } + + extracted += got; + got += offset; + cur_npages = DIV_ROUND_UP(got, PAGE_SIZE); + + for (unsigned int i = 0; i < cur_npages; i++) { + size_t len = umin(got, PAGE_SIZE); + + bvec_set_page(&bq->bv[bq->nr_segs], + *pages++, len - offset, offset); + bq->nr_segs++; + got -= len; + offset = 0; + } + } while (extracted < orig_len && !bvecq_is_full(bq)); + } while (extracted < orig_len && max_segs > 0); + + 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 f9ad067a0a0c..b146aeaaf6c9 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -448,6 +448,9 @@ 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);