take iov_iter stuff to mm/iov_iter.c

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 224 insertions, 0 deletions

diff --git a/mm/iov_iter.c b/mm/iov_iter.c
new file mode 100644
index 000000000000..10e46cd721de
--- /dev/null
+++ b/mm/iov_iter.c
@@ -0,0 +1,224 @@
+#include <linux/export.h>
+#include <linux/uio.h>
+#include <linux/pagemap.h>
+
+size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
+                         struct iov_iter *i)
+{
+        size_t skip, copy, left, wanted;
+        const struct iovec *iov;
+        char __user *buf;
+        void *kaddr, *from;
+
+        if (unlikely(bytes > i->count))
+                bytes = i->count;
+
+        if (unlikely(!bytes))
+                return 0;
+
+        wanted = bytes;
+        iov = i->iov;
+        skip = i->iov_offset;
+        buf = iov->iov_base + skip;
+        copy = min(bytes, iov->iov_len - skip);
+
+        if (!fault_in_pages_writeable(buf, copy)) {
+                kaddr = kmap_atomic(page);
+                from = kaddr + offset;
+
+                /* first chunk, usually the only one */
+                left = __copy_to_user_inatomic(buf, from, copy);
+                copy -= left;
+                skip += copy;
+                from += copy;
+                bytes -= copy;
+
+                while (unlikely(!left && bytes)) {
+                        iov++;
+                        buf = iov->iov_base;
+                        copy = min(bytes, iov->iov_len);
+                        left = __copy_to_user_inatomic(buf, from, copy);
+                        copy -= left;
+                        skip = copy;
+                        from += copy;
+                        bytes -= copy;
+                }
+                if (likely(!bytes)) {
+                        kunmap_atomic(kaddr);
+                        goto done;
+                }
+                offset = from - kaddr;
+                buf += copy;
+                kunmap_atomic(kaddr);
+                copy = min(bytes, iov->iov_len - skip);
+        }
+        /* Too bad - revert to non-atomic kmap */
+        kaddr = kmap(page);
+        from = kaddr + offset;
+        left = __copy_to_user(buf, from, copy);
+        copy -= left;
+        skip += copy;
+        from += copy;
+        bytes -= copy;
+        while (unlikely(!left && bytes)) {
+                iov++;
+                buf = iov->iov_base;
+                copy = min(bytes, iov->iov_len);
+                left = __copy_to_user(buf, from, copy);
+                copy -= left;
+                skip = copy;
+                from += copy;
+                bytes -= copy;
+        }
+        kunmap(page);
+done:
+        i->count -= wanted - bytes;
+        i->nr_segs -= iov - i->iov;
+        i->iov = iov;
+        i->iov_offset = skip;
+        return wanted - bytes;
+}
+EXPORT_SYMBOL(copy_page_to_iter);
+
+static size_t __iovec_copy_from_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_from_user_inatomic(vaddr, buf, 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 successfully copied.  If a fault is encountered then return the number of
+ * bytes which were copied.
+ */
+size_t iov_iter_copy_from_user_atomic(struct page *page,
+                struct iov_iter *i, unsigned long offset, size_t bytes)
+{
+        char *kaddr;
+        size_t copied;
+
+        kaddr = kmap_atomic(page);
+        if (likely(i->nr_segs == 1)) {
+                int left;
+                char __user *buf = i->iov->iov_base + i->iov_offset;
+                left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
+                copied = bytes - left;
+        } else {
+                copied = __iovec_copy_from_user_inatomic(kaddr + offset,
+                                                i->iov, i->iov_offset, bytes);
+        }
+        kunmap_atomic(kaddr);
+
+        return copied;
+}
+EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
+
+/*
+ * This has the same sideeffects and return value as
+ * iov_iter_copy_from_user_atomic().
+ * The difference is that it attempts to resolve faults.
+ * Page must not be locked.
+ */
+size_t iov_iter_copy_from_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_from_user(kaddr + offset, buf, bytes);
+                copied = bytes - left;
+        } else {
+                copied = __iovec_copy_from_user_inatomic(kaddr + offset,
+                                                i->iov, i->iov_offset, bytes);
+        }
+        kunmap(page);
+        return copied;
+}
+EXPORT_SYMBOL(iov_iter_copy_from_user);
+
+void iov_iter_advance(struct iov_iter *i, size_t bytes)
+{
+        BUG_ON(i->count < bytes);
+
+        if (likely(i->nr_segs == 1)) {
+                i->iov_offset += bytes;
+                i->count -= bytes;
+        } else {
+                const struct iovec *iov = i->iov;
+                size_t base = i->iov_offset;
+                unsigned long nr_segs = i->nr_segs;
+
+                /*
+                 * The !iov->iov_len check ensures we skip over unlikely
+                 * zero-length segments (without overruning the iovec).
+                 */
+                while (bytes || unlikely(i->count && !iov->iov_len)) {
+                        int copy;
+
+                        copy = min(bytes, iov->iov_len - base);
+                        BUG_ON(!i->count || i->count < copy);
+                        i->count -= copy;
+                        bytes -= copy;
+                        base += copy;
+                        if (iov->iov_len == base) {
+                                iov++;
+                                nr_segs--;
+                                base = 0;
+                        }
+                }
+                i->iov = iov;
+                i->iov_offset = base;
+                i->nr_segs = nr_segs;
+        }
+}
+EXPORT_SYMBOL(iov_iter_advance);
+
+/*
+ * Fault in the first iovec of the given iov_iter, to a maximum length
+ * of bytes. Returns 0 on success, or non-zero if the memory could not be
+ * accessed (ie. because it is an invalid address).
+ *
+ * writev-intensive code may want this to prefault several iovecs -- that
+ * would be possible (callers must not rely on the fact that _only_ the
+ * first iovec will be faulted with the current implementation).
+ */
+int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
+{
+        char __user *buf = i->iov->iov_base + i->iov_offset;
+        bytes = min(bytes, i->iov->iov_len - i->iov_offset);
+        return fault_in_pages_readable(buf, bytes);
+}
+EXPORT_SYMBOL(iov_iter_fault_in_readable);
+
+/*
+ * Return the count of just the current iov_iter segment.
+ */
+size_t iov_iter_single_seg_count(const struct iov_iter *i)
+{
+        const struct iovec *iov = i->iov;
+        if (i->nr_segs == 1)
+                return i->count;
+        else
+                return min(i->count, iov->iov_len - i->iov_offset);
+}
+EXPORT_SYMBOL(iov_iter_single_seg_count);