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 <[email protected]> cc: Paulo Alcantara <[email protected]> cc: Matthew Wilcox <[email protected]> cc: Christoph Hellwig <[email protected]> cc: Steve French <[email protected]> cc: [email protected] cc: [email protected] cc: [email protected] --- fs/netfs/iterator.c | 125 ++++++++++++++++++++++++++++++++++++++++++ include/linux/netfs.h | 3 + 2 files changed, 128 insertions(+) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index b375567e0520..d2c3055a488c 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -13,6 +13,131 @@ #include <linux/netfs.h> #include "internal.h" +/** + * netfs_extract_iter - Extract virtually contiguous pages from an iterator into a bvecq + * @orig: The original iterator + * @max_len: Maximum number of bytes to extract + * @max_pages: Maximum number of pages to extract + * @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 virtually contiguous page fragments from the source iterator up to + * the given maxima 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 max_len, size_t max_pages, + 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; + + _enter("{%u,%zx},%zx", orig->iter_type, orig->count, max_len); + + if (max_len > orig->count) + max_len = orig->count; + if (WARN_ON_ONCE(!max_len || !max_pages)) + return 0; + + max_pages = iov_iter_npages(orig, max_pages); + if (!max_pages) + return 0; + + do { + struct bvecq *bq; + + bq = bvecq_alloc_one(max_pages, GFP_NOFS); + if (!bq) { + ret = -ENOMEM; + break; + } + if (user_backed_iter(orig)) + bq->mem_type = iov_iter_extract_will_pin(orig) ? + BVECQ_MEM_GUP : BVECQ_MEM_PAGECACHE; + bq->prev = bq_tail; + bq->fpos = fpos + extracted; + + if (bq_tail) + bq_tail->next = bq; + else + *_bvecq_head = bq; + bq_tail = bq; + + if (max_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, max_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, max_len); + ret = -EIO; + goto out; + } + + if (WARN(got > max_len, + "%s: extract_pages overrun %zd > %zu bytes\n", + __func__, got, max_len)) { + ret = -EIO; + break; + } + + extracted += got; + max_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 (max_len > 0 && !bvecq_is_full(bq)); + + max_pages -= bq->nr_slots; + } while (max_len > 0 && max_pages > 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 12e5c51c11c8..40f45ecf1db8 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -460,6 +460,9 @@ 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 max_len, size_t max_pages, + 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);
