Re: [PATCH v3 1/3] vmcore: Convert copy_oldmem_page() to take an iov_iter

Baoquan He
2021-12-20T08:10:57Z

On 12/13/21 at 02:39pm, Matthew Wilcox (Oracle) wrote:
> Instead of passing in a 'buf' and 'userbuf' argument, pass in an iov_iter.
> s390 needs more work to pass the iov_iter down further, or refactor,
> but I'd be more comfortable if someone who can test on s390 did that work.
>
> It's more convenient to convert the whole of read_from_oldmem() to
> take an iov_iter at the same time, so rename it to read_from_oldmem_iter()
> and add a temporary read_from_oldmem() wrapper that creates an iov_iter.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Thanks for making this to do an awesome clean up. This one looks good to
me.

Acked-by: Baoquan He <bhe@redhat.com>

......
> -/**
> - * copy_oldmem_page() - copy one page from old kernel memory
> - * @pfn: page frame number to be copied
> - * @buf: buffer where the copied page is placed
> - * @csize: number of bytes to copy
> - * @offset: offset in bytes into the page
> - * @userbuf: if set, @buf is int he user address space
> - *
> - * This function copies one page from old kernel memory into buffer pointed by
> - * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
> - * copied or negative error in case of failure.
> - */
> -ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
> - size_t csize, unsigned long offset,
> - int userbuf)
> +ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn,
> + size_t csize, unsigned long offset)
^^^^^^
I am curious why this parameter is called 'csize', but not 'size' directly.
This is not related to this patch, it's an old naming.

> {
> void *vaddr;
>
> @@ -40,14 +28,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
> if (!vaddr)
> return -ENOMEM;
>
> - if (userbuf) {
> - if (copy_to_user(buf, vaddr + offset, csize)) {
> - iounmap(vaddr);
> - return -EFAULT;
> - }
> - } else {
> - memcpy(buf, vaddr + offset, csize);
> - }
> + csize = copy_to_iter(vaddr + offset, csize, iter);
>
> iounmap(vaddr);
> return csize;