Provide a function for filling in a scatterlist from the list of pages
contained in an iterator.
If the iterator is UBUF- or IOBUF-type, the pages have a ref taken on them.
If the iterator is BVEC-, KVEC- or XARRAY-type, no ref is taken on the
pages and it is left to the caller to manage their lifetime. It cannot be
assumed that a ref can be validly taken, particularly in the case of a KVEC
iterator.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: Steve French <sfrench@xxxxxxxxx>
cc: Shyam Prasad N <nspmangalore@xxxxxxxxx>
cc: Rohith Surabattula <rohiths.msft@xxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
cc: linux-cifs@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
fs/netfs/iterator.c | 252 +++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/netfs.h | 3 +
2 files changed, 255 insertions(+)
diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c
index c11d05a66a4a..62485416cc3d 100644
--- a/fs/netfs/iterator.c
+++ b/fs/netfs/iterator.c
@@ -7,7 +7,9 @@
#include <linux/export.h>
#include <linux/slab.h>
+#include <linux/mm.h>
#include <linux/uio.h>
+#include <linux/scatterlist.h>
#include <linux/netfs.h>
#include "internal.h"
@@ -92,3 +94,253 @@ ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len,
return npages;
}
EXPORT_SYMBOL(netfs_extract_user_iter);
+
+/*
+ * Extract and pin up to sg_max pages from UBUF- or IOVEC-class iterators and
+ * add them to the scatterlist.
+ */
+static ssize_t netfs_extract_user_to_sg(struct iov_iter *iter,
+ ssize_t maxsize,
+ struct sg_table *sgtable,
+ unsigned int sg_max)
+{
+ struct scatterlist *sg = sgtable->sgl + sgtable->nents;
+ struct page **pages;
+ unsigned int npages;
+ ssize_t ret = 0, res;
+ size_t len, off;
+
+ /* We decant the page list into the tail of the scatterlist */
+ pages = (void *)sgtable->sgl + array_size(sg_max, sizeof(struct scatterlist));
+ pages -= sg_max;
+
+ do {
+ res = iov_iter_get_pages2(iter, pages, maxsize, sg_max, &off);
+ if (res < 0)
+ goto failed;
+
+ len = res;
+ maxsize -= len;
+ ret += len;
+ npages = DIV_ROUND_UP(off + len, PAGE_SIZE);
+ sg_max -= npages;
+
+ for (; npages < 0; npages--) {
+ struct page *page = *pages;
+ size_t seg = min_t(size_t, PAGE_SIZE - off, len);
+
+ *pages++ = NULL;
+ sg_set_page(sg, page, len, off);
+ sgtable->nents++;
+ sg++;
+ len -= seg;
+ off = 0;
+ }
+ } while (maxsize > 0 && sg_max > 0);
+
+ return ret;
+
+failed:
+ while (sgtable->nents > sgtable->orig_nents)
+ put_page(sg_page(&sgtable->sgl[--sgtable->nents]));
+ return res;
+}
+
+/*
+ * Extract up to sg_max pages from a BVEC-type iterator and add them to the
+ * scatterlist. The pages are not pinned.
+ */
+static ssize_t netfs_extract_bvec_to_sg(struct iov_iter *iter,
+ ssize_t maxsize,
+ struct sg_table *sgtable,
+ unsigned int sg_max)
+{
+ const struct bio_vec *bv = iter->bvec;
+ struct scatterlist *sg = sgtable->sgl + sgtable->nents;
+ unsigned long start = iter->iov_offset;
+ unsigned int i;
+ ssize_t ret = 0;
+
+ for (i = 0; i < iter->nr_segs; i++) {
+ size_t off, len;
+
+ len = bv[i].bv_len;
+ if (start >= len) {
+ start -= len;
+ continue;
+ }
+
+ len = min_t(size_t, maxsize, len - start);
+ off = bv[i].bv_offset + start;
+
+ sg_set_page(sg, bv[i].bv_page, len, off);
+ sgtable->nents++;
+ sg++;
+ sg_max--;
+
+ ret += len;
+ maxsize -= len;
+ if (maxsize <= 0 || sg_max == 0)
+ break;
+ start = 0;
+ }
+
+ if (ret > 0)
+ iov_iter_advance(iter, ret);
+ return ret;
+}
+
+/*
+ * Extract up to sg_max pages from a KVEC-type iterator and add them to the
+ * scatterlist. This can deal with vmalloc'd buffers as well as kmalloc'd or
+ * static buffers. The pages are not pinned.
+ */
+static ssize_t netfs_extract_kvec_to_sg(struct iov_iter *iter,
+ ssize_t maxsize,
+ struct sg_table *sgtable,
+ unsigned int sg_max)
+{
+ const struct kvec *kv = iter->kvec;
+ struct scatterlist *sg = sgtable->sgl + sgtable->nents;
+ unsigned long start = iter->iov_offset;
+ unsigned int i;
+ ssize_t ret = 0;
+
+ for (i = 0; i < iter->nr_segs; i++) {
+ struct page *page;
+ unsigned long kaddr;
+ size_t off, len, seg;
+
+ len = kv[i].iov_len;
+ if (start >= len) {
+ start -= len;
+ continue;
+ }
+
+ kaddr = (unsigned long)kv[i].iov_base + start;
+ off = kaddr & ~PAGE_MASK;
+ len = min_t(size_t, maxsize, len - start);
+ kaddr &= PAGE_MASK;
+
+ maxsize -= len;
+ ret += len;
+ do {
+ seg = min_t(size_t, len, PAGE_SIZE - off);
+ if (is_vmalloc_or_module_addr((void *)kaddr))
+ page = vmalloc_to_page((void *)kaddr);
+ else
+ page = virt_to_page(kaddr);
+
+ sg_set_page(sg, page, len, off);
+ sgtable->nents++;
+ sg++;
+ sg_max--;
+
+ len -= seg;
+ kaddr += PAGE_SIZE;
+ off = 0;
+ } while (len > 0 && sg_max > 0);
+
+ if (maxsize <= 0 || sg_max == 0)
+ break;
+ start = 0;
+ }
+
+ if (ret > 0)
+ iov_iter_advance(iter, ret);
+ return ret;
+}
+
+/*
+ * Extract up to sg_max folios from an XARRAY-type iterator and add them to
+ * the scatterlist. The pages are not pinned.
+ */
+static ssize_t netfs_extract_xarray_to_sg(struct iov_iter *iter,
+ ssize_t maxsize,
+ struct sg_table *sgtable,
+ unsigned int sg_max)
+{
+ struct scatterlist *sg = sgtable->sgl + sgtable->nents;
+ struct xarray *xa = iter->xarray;
+ struct folio *folio;
+ loff_t start = iter->xarray_start + iter->iov_offset;
+ pgoff_t index = start / PAGE_SIZE;
+ ssize_t ret = 0;
+ size_t offset, len;
+ XA_STATE(xas, xa, index);
+
+ rcu_read_lock();
+
+ xas_for_each(&xas, folio, ULONG_MAX) {
+ if (xas_retry(&xas, folio))
+ continue;
+ if (WARN_ON(xa_is_value(folio)))
+ break;
+ if (WARN_ON(folio_test_hugetlb(folio)))
+ break;
+
+ offset = offset_in_folio(folio, start);
+ len = min_t(size_t, maxsize, folio_size(folio) - offset);
+
+ sg_set_page(sg, folio_page(folio, 0), len, offset);
+ sgtable->nents++;
+ sg++;
+ sg_max--;
+
+ maxsize -= len;
+ ret += len;
+ if (maxsize <= 0 || sg_max == 0)
+ break;
+ }
+
+ rcu_read_unlock();
+ if (ret > 0)
+ iov_iter_advance(iter, ret);
+ return ret;
+}
+
+/**
+ * netfs_extract_iter_to_sg - Extract pages from an iterator and add ot an sglist
+ * @iter: The iterator to extract from
+ * @maxsize: The amount of iterator to copy
+ * @sgtable: The scatterlist table to fill in
+ * @sg_max: Maximum number of elements in @sgtable that may be filled
+ *
+ * Extract the page fragments from the given amount of the source iterator and
+ * add them to a scatterlist that refers to all of those bits, to a maximum
+ * addition of @sg_max elements.
+ *
+ * The pages referred to by UBUF- and IOVEC-type iterators are extracted and
+ * pinned; BVEC-, KVEC- and XARRAY-type are extracted but aren't pinned; PIPE-
+ * and DISCARD-type are not supported.
+ *
+ * No end mark is placed on the scatterlist; that's left to the caller.
+ *
+ * If successul, @sgtable->nents is updated to include the number of elements
+ * added and the number of bytes added is returned. @sgtable->orig_nents is
+ * left unaltered.
+ */
+ssize_t netfs_extract_iter_to_sg(struct iov_iter *iter, size_t maxsize,
+ struct sg_table *sgtable, unsigned int sg_max)
+{
+ if (maxsize == 0)
+ return 0;
+
+ switch (iov_iter_type(iter)) {
+ case ITER_UBUF:
+ case ITER_IOVEC:
+ return netfs_extract_user_to_sg(iter, maxsize, sgtable, sg_max);
+ case ITER_BVEC:
+ return netfs_extract_bvec_to_sg(iter, maxsize, sgtable, sg_max);
+ case ITER_KVEC:
+ return netfs_extract_kvec_to_sg(iter, maxsize, sgtable, sg_max);
+ case ITER_XARRAY:
+ return netfs_extract_xarray_to_sg(iter, maxsize, sgtable, sg_max);
+ default:
+ pr_err("netfs_extract_iter_to_sg(%u) unsupported\n",
+ iov_iter_type(iter));
+ WARN_ON_ONCE(1);
+ return -EIO;
+ }
+}
+EXPORT_SYMBOL(netfs_extract_iter_to_sg);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 5f6ad0246946..21771dd594a1 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -290,6 +290,9 @@ void netfs_put_subrequest(struct netfs_io_subrequest *subreq,
void netfs_stats_show(struct seq_file *);
ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len,
struct iov_iter *new);
+struct sg_table;
+ssize_t netfs_extract_iter_to_sg(struct iov_iter *iter, size_t len,
+ struct sg_table *sgtable, unsigned int sg_max);
/**
* netfs_inode - Get the netfs inode context from the inode
