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authorAndreas Gruenbacher <agruenba@redhat.com>2022-04-15 06:28:41 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2022-05-01 17:22:29 +0200
commit1d91c912e7d14e147183757f48e709f8154f9de3 (patch)
tree6bb7b6709dec6561636c0b91662eac2e9186a341 /lib
parent30e66b1dfcbbe409c76500a77ecd20b3cf5b8fa5 (diff)
iov_iter: Introduce fault_in_iov_iter_writeable
commit cdd591fc86e38ad3899196066219fbbd845f3162 upstream Introduce a new fault_in_iov_iter_writeable helper for safely faulting in an iterator for writing. Uses get_user_pages() to fault in the pages without actually writing to them, which would be destructive. We'll use fault_in_iov_iter_writeable in gfs2 once we've determined that the iterator passed to .read_iter isn't in memory. Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Signed-off-by: Anand Jain <anand.jain@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/iov_iter.c39
1 files changed, 39 insertions, 0 deletions
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index b8de180420c7..b137da9afd7a 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -468,6 +468,45 @@ size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t size)
}
EXPORT_SYMBOL(fault_in_iov_iter_readable);
+/*
+ * fault_in_iov_iter_writeable - fault in iov iterator for writing
+ * @i: iterator
+ * @size: maximum length
+ *
+ * Faults in the iterator using get_user_pages(), i.e., without triggering
+ * hardware page faults. This is primarily useful when we already know that
+ * some or all of the pages in @i aren't in memory.
+ *
+ * Returns the number of bytes not faulted in, like copy_to_user() and
+ * copy_from_user().
+ *
+ * Always returns 0 for non-user-space iterators.
+ */
+size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t size)
+{
+ if (iter_is_iovec(i)) {
+ size_t count = min(size, iov_iter_count(i));
+ const struct iovec *p;
+ size_t skip;
+
+ size -= count;
+ for (p = i->iov, skip = i->iov_offset; count; p++, skip = 0) {
+ size_t len = min(count, p->iov_len - skip);
+ size_t ret;
+
+ if (unlikely(!len))
+ continue;
+ ret = fault_in_safe_writeable(p->iov_base + skip, len);
+ count -= len - ret;
+ if (ret)
+ break;
+ }
+ return count + size;
+ }
+ return 0;
+}
+EXPORT_SYMBOL(fault_in_iov_iter_writeable);
+
void iov_iter_init(struct iov_iter *i, unsigned int direction,
const struct iovec *iov, unsigned long nr_segs,
size_t count)