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Subject[RFC PATCH v2 02/21] iov_iter: add copy_to_user support
Date
From: Zach Brown <zab@zabbo.net>

This adds iov_iter wrappers around copy_to_user() to match the existing
wrappers around copy_from_user().

This will be used by the generic file system buffered read path.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
---
include/linux/fs.h | 4 +++
mm/iov-iter.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 82 insertions(+)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 69cd5bb..bc65cc2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -535,6 +535,10 @@ struct iov_iter {
size_t count;
};

+size_t iov_iter_copy_to_user_atomic(struct page *page,
+ struct iov_iter *i, unsigned long offset, size_t bytes);
+size_t iov_iter_copy_to_user(struct page *page,
+ struct iov_iter *i, unsigned long offset, size_t bytes);
size_t iov_iter_copy_from_user_atomic(struct page *page,
struct iov_iter *i, unsigned long offset, size_t bytes);
size_t iov_iter_copy_from_user(struct page *page,
diff --git a/mm/iov-iter.c b/mm/iov-iter.c
index 596fcf0..eea21ea 100644
--- a/mm/iov-iter.c
+++ b/mm/iov-iter.c
@@ -6,6 +6,84 @@
#include <linux/highmem.h>
#include <linux/pagemap.h>

+static size_t __iovec_copy_to_user_inatomic(char *vaddr,
+ const struct iovec *iov, size_t base, size_t bytes)
+{
+ size_t copied = 0, left = 0;
+
+ while (bytes) {
+ char __user *buf = iov->iov_base + base;
+ int copy = min(bytes, iov->iov_len - base);
+
+ base = 0;
+ left = __copy_to_user_inatomic(buf, vaddr, copy);
+ copied += copy;
+ bytes -= copy;
+ vaddr += copy;
+ iov++;
+
+ if (unlikely(left))
+ break;
+ }
+ return copied - left;
+}
+
+/*
+ * Copy as much as we can into the page and return the number of bytes which
+ * were sucessfully copied. If a fault is encountered then return the number of
+ * bytes which were copied.
+ */
+size_t iov_iter_copy_to_user_atomic(struct page *page,
+ struct iov_iter *i, unsigned long offset, size_t bytes)
+{
+ char *kaddr;
+ size_t copied;
+
+ BUG_ON(!in_atomic());
+ kaddr = kmap_atomic(page, KM_USER0);
+ if (likely(i->nr_segs == 1)) {
+ int left;
+ char __user *buf = i->iov->iov_base + i->iov_offset;
+ left = __copy_to_user_inatomic(buf, kaddr + offset, bytes);
+ copied = bytes - left;
+ } else {
+ copied = __iovec_copy_to_user_inatomic(kaddr + offset,
+ i->iov, i->iov_offset, bytes);
+ }
+ kunmap_atomic(kaddr, KM_USER0);
+
+ return copied;
+}
+EXPORT_SYMBOL(iov_iter_copy_to_user_atomic);
+
+/*
+ * This has the same sideeffects and return value as
+ * iov_iter_copy_to_user_atomic().
+ * The difference is that it attempts to resolve faults.
+ * Page must not be locked.
+ */
+size_t iov_iter_copy_to_user(struct page *page,
+ struct iov_iter *i, unsigned long offset, size_t bytes)
+{
+ char *kaddr;
+ size_t copied;
+
+ kaddr = kmap(page);
+ if (likely(i->nr_segs == 1)) {
+ int left;
+ char __user *buf = i->iov->iov_base + i->iov_offset;
+ left = copy_to_user(buf, kaddr + offset, bytes);
+ copied = bytes - left;
+ } else {
+ copied = __iovec_copy_to_user_inatomic(kaddr + offset,
+ i->iov, i->iov_offset, bytes);
+ }
+ kunmap(page);
+ return copied;
+}
+EXPORT_SYMBOL(iov_iter_copy_to_user);
+
+
static size_t __iovec_copy_from_user_inatomic(char *vaddr,
const struct iovec *iov, size_t base, size_t bytes)
{
--
1.7.9.5


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