From f0d1bec9d58d4c038d0ac958c9af82be6eb18045 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Thu, 3 Apr 2014 15:05:18 -0400 Subject: new helper: copy_page_from_iter() parallel to copy_page_to_iter(). pipe_write() switched to it (and became ->write_iter()). Signed-off-by: Al Viro --- mm/iov_iter.c | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) (limited to 'mm/iov_iter.c') diff --git a/mm/iov_iter.c b/mm/iov_iter.c index a5c691c..081e327 100644 --- a/mm/iov_iter.c +++ b/mm/iov_iter.c @@ -82,6 +82,84 @@ done: } EXPORT_SYMBOL(copy_page_to_iter); +size_t copy_page_from_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, *to; + + 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_readable(buf, copy)) { + kaddr = kmap_atomic(page); + to = kaddr + offset; + + /* first chunk, usually the only one */ + left = __copy_from_user_inatomic(to, buf, copy); + copy -= left; + skip += copy; + to += copy; + bytes -= copy; + + while (unlikely(!left && bytes)) { + iov++; + buf = iov->iov_base; + copy = min(bytes, iov->iov_len); + left = __copy_from_user_inatomic(to, buf, copy); + copy -= left; + skip = copy; + to += copy; + bytes -= copy; + } + if (likely(!bytes)) { + kunmap_atomic(kaddr); + goto done; + } + offset = to - kaddr; + buf += copy; + kunmap_atomic(kaddr); + copy = min(bytes, iov->iov_len - skip); + } + /* Too bad - revert to non-atomic kmap */ + kaddr = kmap(page); + to = kaddr + offset; + left = __copy_from_user(to, buf, copy); + copy -= left; + skip += copy; + to += copy; + bytes -= copy; + while (unlikely(!left && bytes)) { + iov++; + buf = iov->iov_base; + copy = min(bytes, iov->iov_len); + left = __copy_from_user(to, buf, copy); + copy -= left; + skip = copy; + to += 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_from_iter); + static size_t __iovec_copy_from_user_inatomic(char *vaddr, const struct iovec *iov, size_t base, size_t bytes) { -- cgit v1.1