[PATCHv6 08/11] iov: introduce iov_iter_aligned

Keith Busch
2022-06-10T20:16:16Z

From: Keith Busch <kbusch@kernel.org>

The existing iov_iter_alignment() function returns the logical OR of
address and length. For cases where address and length need to be
considered separately, introduce a helper function that a caller can
specificy length and address masks that indicate if the iov is
unaligned.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
include/linux/uio.h | 2 +
lib/iov_iter.c | 92 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 94 insertions(+)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 739285fe5a2f..34ba4a731179 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -219,6 +219,8 @@ size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
#endif

size_t iov_iter_zero(size_t bytes, struct iov_iter *);
+bool iov_iter_is_aligned(const struct iov_iter *i, unsigned addr_mask,
+ unsigned len_mask);
unsigned long iov_iter_alignment(const struct iov_iter *i);
unsigned long iov_iter_gap_alignment(const struct iov_iter *i);
void iov_iter_init(struct iov_iter *i, unsigned int direction, const struct iovec *iov,
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 6dd5330f7a99..a39b24496878 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1268,6 +1268,98 @@ void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)
}
EXPORT_SYMBOL(iov_iter_discard);

+static bool iov_iter_aligned_iovec(const struct iov_iter *i, unsigned addr_mask,
+ unsigned len_mask)
+{
+ size_t size = i->count;
+ size_t skip = i->iov_offset;
+ unsigned k;
+
+ for (k = 0; k < i->nr_segs; k++, skip = 0) {
+ size_t len = i->iov[k].iov_len - skip;
+
+ if (len > size)
+ len = size;
+ if (len & len_mask)
+ return false;
+ if ((unsigned long)(i->iov[k].iov_base + skip) & addr_mask)
+ return false;
+
+ size -= len;
+ if (!size)
+ break;
+ }
+ return true;
+}
+
+static bool iov_iter_aligned_bvec(const struct iov_iter *i, unsigned addr_mask,
+ unsigned len_mask)
+{
+ size_t size = i->count;
+ unsigned skip = i->iov_offset;
+ unsigned k;
+
+ for (k = 0; k < i->nr_segs; k++, skip = 0) {
+ size_t len = i->bvec[k].bv_len - skip;
+
+ if (len > size)
+ len = size;
+ if (len & len_mask)
+ return false;
+ if ((unsigned long)(i->bvec[k].bv_offset + skip) & addr_mask)
+ return false;
+
+ size -= len;
+ if (!size)
+ break;
+ }
+ return true;
+}
+
+/**
+ * iov_iter_is_aligned() - Check if the addresses and lengths of each segments
+ * are aligned to the parameters.
+ *
+ * @i: &struct iov_iter to restore
+ * @addr_mask: bit mask to check against the iov element's addresses
+ * @len_mask: bit mask to check against the iov element's lengths
+ *
+ * Return: false if any addresses or lengths intersect with the provided masks
+ */
+bool iov_iter_is_aligned(const struct iov_iter *i, unsigned addr_mask,
+ unsigned len_mask)
+{
+ if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
+ return iov_iter_aligned_iovec(i, addr_mask, len_mask);
+
+ if (iov_iter_is_bvec(i))
+ return iov_iter_aligned_bvec(i, addr_mask, len_mask);
+
+ if (iov_iter_is_pipe(i)) {
+ unsigned int p_mask = i->pipe->ring_size - 1;
+ size_t size = i->count;
+
+ if (size & len_mask)
+ return false;
+ if (size && allocated(&i->pipe->bufs[i->head & p_mask])) {
+ if (i->iov_offset & addr_mask)
+ return false;
+ }
+
+ return true;
+ }
+
+ if (iov_iter_is_xarray(i)) {
+ if (i->count & len_mask)
+ return false;
+ if ((i->xarray_start + i->iov_offset) & addr_mask)
+ return false;
+ }
+
+ return true;
+}
+EXPORT_SYMBOL_GPL(iov_iter_is_aligned);
+
static unsigned long iov_iter_alignment_iovec(const struct iov_iter *i)
{
unsigned long res = 0;
--
2.30.2