On Sun, Apr 29, 2012 at 02:03:41PM -0700, Alexandre Depoutovitch wrote:
> + if (current->mm) {
> + ret = get_user_pages_fast(
> + dio->curr_user_address, /* Where from? */
> + nr_pages, /* How many pages? */
> + dio->rw == READ, /* Write to memory? */
> + &dio->pages[0]); /* Put results here */
> + } else {
> + /* For kernel threads mm is NULL, so all we need is to increment
> + page's reference count and add page to dio->pages array */
> + int i;
> + struct page* page;
> + unsigned long start_pfn = virt_to_phys((void
> *)dio->curr_user_address)
> + >> PAGE_SHIFT;
> + /* For kernel threads buffer must be in kernel memory */
> + BUG_ON(dio->curr_user_address < TASK_SIZE_MAX);
This is an assumption that isn't true for all architectures. Better just
delete this line.
> + for (i = 0; i < nr_pages; i++) {
> + page = pfn_to_page(start_pfn + i);
Why are you messing about with pfns? Why not just stay with virtual
addresses and call virt_to_page() in this loop? That would ensure that
this works to vmapped pages as well as physically contiguous pages.
> + page_cache_get(page);
> + dio->pages[i] = page;
> + }
> + /* No need to lock pages: this is kernel thread and the pages are in
> + kernel as well */
> + ret = nr_pages;
> + }
>
> if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) {
> struct page *page = ZERO_PAGE(0);
> @@ -972,7 +991,11 @@
> break;
> }
>
> - /* Drop the ref which was taken in get_user_pages() */
> + /*
> + * Drop the ref which was taken in dio_refill_pages
> + * directly (for direct I/O) or by calling get_user_pages
> + * (for buffered IO)
> + */
I think your change to this comment actually makes it more confusing.
> @@ -1348,6 +1351,58 @@
> nfsd_max_blksize);
> }
>
> +int nfsd_directio_mode = DIO_NEVER;
> +
> +/**
> + * nfsd_directio_mode - sets conditions when direct IO is activated
> + *
> + * Input:
> + * buf: ignored
> + * size: zero
> + *
> + * OR
> + *
> + * Input:
> + * buf: C string containing an unsigned
> + * integer value representing the new
> + * NFS direct IO mode
> + * size: non-zero length of C string in @buf
> + * Output:
> + * On success: passed-in buffer filled with '\n'-terminated C string
> + * containing numeric value of the current direct IO mode
> + * return code is the size in bytes of the string
> + *
> + * Possible modes are:
> + * DIO_NEVER (0) - never use direct I/O
> + * DIO_FS_UNALIGNED (1) - use direct I/O only for requests that FS
> unaligned
> + * and block device aligned
> + * DIO_SECTOR_ALIGNED (3) - use direct I/O for all block device aligned
> IO
> + * On error: return code is zero or a negative errno value
> + */
This is not correct kerneldoc formatting.
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
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